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LTD-9 Abstracts

A01. Magnetic Sensors for X-Ray and Gamma-Ray Detection

C. Enss
Kirchhoff-Institut für Physik
Universität Heidelberg, D-69120 Heidelberg, Germany

In recent years metallic magnetic calorimeters have been developed for particle detection. A magnetic calorimeter consists of an absorber suited for the particles to be detected, which is weakly coupled to a thermal bath and a paramagnetic sensor located in a small magnetic field as thermometer, which should be intimately coupled to the absorber. The energy deposition of an incident particle leads to a change of the absorber temperature and thus to a change of the magnetization of the sensor. This change in magnetization can be measured with high resolution using a sensitive DC-SQUID. To meet the requirements in terms of detector speed, magnetic sensors with metallic hosts doped with rare earth ions are preferable. A material of this type, which has been studied in detail in recent years is gold containing a few hundred ppm erbium ions. The performance of metallic magnetic calorimeters based on Au:Er has improved rapidly and has now reached a level where various applications are conceivable. We discuss the principle of operation and the optimization criteria of magnetic calorimeters, the design and performance of prototype detectors for both x-ray and gamma-ray, detection and the fundamental limits of the energy resolution of such detectors.

A02. Large-format Distributed Read-Out Imaging Devices for Optical and X-ray Imaging Spectroscopy

Roland den Hartog^a, D. Martin^a, A. Kozorezov^b, P. Verhoeve^a, G. Brammertz^a, A. Peacock^a, F. Scholze^c, D.J Goldie^d
a Astrophysics Division, Space Science Dept. of the European Space Agency, ESTEC, P.O. Box 299, 2200 AG Noordwijk, The Netherlands
^b School of Chemistry and Physics, Lancaster University, Lancaster LA1 4YB, U.K.
^c Physikalisch-Technische Bundesanstalt (PTB), Abbestr. 2-12, D-10587 Berlin, Germany
^d Oxford Instruments Scientific Research Division, Newton House, Cambridge Business Park, Cambridge CB4 4WY, U.K.

We present an experimental study of the performance of Distributed Read-Out Imaging Devices (DROIDs), based on two Ta/Al-based STJs placed on either side of a Ta absorber strip. We focus our discussion on the prospects of building large-format photon-counting imaging spectrometers for applications at optical, UV and soft X-ray energies. Tunnel-limited spectroscopical resolutions have already been demonstrated for optical photons. With a 20 × 100 µm² absorber we have measured an intrinsic energy resolution of 2 eV FWHM for 500 eV photons. This demonstrates that at soft X-ray energies resolutions close to the tunnel limit are also feasible for these type of detectors. A detailed analysis of pulse-shapes with numerical models allows us to assess the main parameters that determine the performance of these detectors. In particular, we discuss the dependence of the quasiparticle diffusion constant on the temperature of the absorber. Extrapolation of these models indicates that it is possible to extend the length of the absorber to 1.5 mm, without a serious degradation of the detector's performance.

A03. Approaching Intrinsic Resolution Limits in Optical/UV Superconducting Tunnel Junction Detectors

C.M. Wilson^a, L. Frunzio^a, L. Li ^a, D.E. Prober^a, T. Stevenson^b, C. Stahle^b
aYale University, New Haven, CT
^bNASA Goddard Spaceflight Center, Greenbelt, MD

We present results of development of imaging superconducting tunnel junction detectors in the optical/UV energy range. Our detectors have a Ta strip absorber with Al tunnel junctions located on the two ends of the strip. The tunnel junction area does not overlap the absorber. Using devices designed for large backtunneling gain, we have measured an energy resolution of 0.4 eV at 4.89 eV. The resolution in these devices is limited by thermodynamic fluctuations of the thermal quasiparticle number in the Al trapping layers. We predict that this previously unconsidered noise source should be important in any device with "deep" traps. We are currently developing detectors designed to eliminate this noise and, consequently, backtunneling gain. These devices need small junctions, of order 1 square micron, for best noise performance. We are currently developing an electron beam lithography process to produce these junctions. The resolution of these devices should approach the intrinsic limits of creation and trapping statistics, and exceed the resolution of devices with backtunneling. We will present preliminary measurements of these new devices made with conventional FET amplifiers and with a new radio frequency single electron transistor amplifier (RF-SET).

A04. Factors of inhomogeneous spatial response of superconducting tunnel junction detectors

H. Pressler^a, M. Ohkubo^a, M. Koike^a, M. Ukibe^a, T. Zama^a
a National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan

Spatial uniformity in response of superconducting tunnel junction detectors to photons is a main concern in the detector development. Low Temperature Scanning Synchrotron Microscopy (LTSSM) has been used to directly image spatial profiles of response of Nb-based superconducting tunnel junctions (STJ) to x-ray photons. By scanning an x-ray beam with a diameter of 5 - 10 /mum employed as a microprobe enable visualization of the spectroscopic properties of STJ x-ray detectors at an actual working temperature of about 0.4 K. We have found that the inhomogeneity of the junction response strongly depends on such parameters as junction size, bias current, the strength of applied magnetic field parallel to insulation barriers, and Josephson current density.

A05. Measurement of Quantized Thermal Conductance

K. Schwab^a, M.L. Roukes^b
aLaboratory for Physical Sciences, College Park, MD 20740
^bPhysics Department, Caltech, Pasadena, CA 91125

We have experimentally demonstrated that the thermal conductance through discrete, one-dimensional, ballistic phonon channels is quantized, G=pi²k_B²T/3h. This is the predicted, universal upper-bound for thermal conductance per channel, independent of material characteristics and particle statistics. We have developed novel, 3D nanostructures, with feature sizes of order ~100nm to enter and reveal this mesoscopic limit for phonons. We will describe the techniques and implications of this measurement to nanoscale bolometry, and describe our current work where we are exploring the limits of heat capacity in these and more advanced nanoscale devices from temperatures of ~10K to less than 100mK. Using preliminary bulk estimates and dc-SQUID-based noise thermometry, we anticipate realization of a bolometer with total heat capacity of ~ 10³ k_B, giving microsecond response time and energy sensitivity at the level of single terahertz photons.

A06. Energy resolution Delta E = 12 eV at E = 5.9 keV for lead absorber coupled to a single Al-STJ via phonons only

G. Angloher, M. Huber, J. Jochum, A. R�dig, F. von Feilitzsch, R. L. M��bauer

A superconducting lead absorber (90 x 90 x 1.3 microns³) coupled to a single Al-STJ via phonons only was read out with an energy resolution Delta E = 12 eV at E = 5.9 keV. The whole detector area was illuminated, no software cuts were applied to the ADC data output. Due to the high absorption efficiency of lead (> 50 % at E = 5.9 keV, > 99.9 % if E < 1 keV) and the detector's location on a thin Si3N4-membrane double/multi-peak structures are strongly suppressed in the pulseheight spectra. A signal to background ratio higher than 10³ was achieved for energies higher than E = 1.3 keV. At E = 1.74 keV an energy resolution lower than Delta E = 10 eV was reached, allowing to separate tungsten M-lines and silicon K-lines. The detector stability was limited by the cryostats holding time. Different from Al-STJs on massive substrates, the detector shows linear energy response between E = 1.74 keV and E = 6.49 keV. Degradation of the detector could be avoided by covering the lead absorber with a thin SiO-layer.

A07. Ultrasensitive hot-electron kinetic-inductance detectors

A. Sergeev^a, B. Karasik^b, I. Gogidze^c, V. Mitin^a
aWayne State University, Detroit, MI
^bJet Propulsion Laboratory, California Institute of Technology, Pasadena, CA
^cWinncom Technologies Corp., Solon, OH

Electron heating in thin superconducting films is an underlying physical mechanism for numerous sensors of electromagnetic radiation. Resistive sensors operating in the vicinity of superconducting transition (also known as hot-electron detectors) are already used as ultrafast detectors and broadband THz mixes. Kinetic inductance sensors can be potentially more sensitive due to lower noise, and their parameters (speed, responsivity, noise) can be adjusted in a broad temperature range below T_c. We present the results of measurements of kinetic inductance response in NbN thin films and modeling of noise characteristics for sensors based on Nb, NbN, and MgB films. Our study demonstrates that the photoresponse of NbN films is well described by the Owen-Scalapino model (change of nonequilibrium chemical potential of quasiparticles caused by radiation) with strong phonon re-trapping by condensate which significantly increases the quantum efficiency. The time constant of the sensor is given by the quasiparticle lifetime, which is about 4 ns in a 5-nm thick film at 4.2 K. The results of modeling show that the noise equivalent noise power (NEP) of the detector can be as low as 10^-17-10^-16 W/Hz^-1/2 at 4.2 K. Due to the exponential temperature dependence of the quasiparticle concentration this figure dramatically improves at lower temperature reaching 10^-20 W/Hz^-1/2 at 1 K.

A08. Sensor development for single-photon thermoelectric detectors

A. M. Gulian^a, K. S. Wood^b, G. G. Fritz^b, D. Van Vechten^c, H.D. Wu^b, J. S. Horwitz^b, G. R. Badalyantz^b, S. R. Harutyunyan^d, V. H. Vartanyan^d, V. R. Nikoghosyan^d, S. A. Petrosyan^d, A. S. Kuzanyan^d.
^aUSRA/NRL, Washington, DC
^bNRL, Washington, DC
^cONR, Arlington, VA
^dIPR, Nat'l Acad. Sci., Armenia

As we reported earlier [1], thermoelectric detectors can be competitive as non-dispersive energy resolving focal-plane instruments in X-ray/UV spectrum. The first generations of prototype devices demonstrated the viability of detector design and provided good agreement between theoretical expectations and experimental data. These devices exploited sensors made of gold with a small fraction of iron impurity. To get the projected high resolution one needs other type of material, namely, lanthanum-cerium hexaborides. We report on the first experimental tests of the feasibility of lanthanum-cerium films as sensor materials. Progress with technology of these materials argues for the success of these thermoelectric detectors. [1] A. Gulian, K. Wood, G. Fritz, A. Gyulamiryan, V. Nikogosyan, N. Giordano, T. Jacobs, and D. Van Vechten, X-ray/UV single-photon detectors with isotropic Seebeck sensors, NIMA , 441, No.3 (2000).

A09. Quasi-particle diffusion and the energy resolution of superconducting tunneling junctions as photon detectors.

Roland den Hartog^a, A.G. Kozorezov^b, J.K. Wigmore^b, D. Martin^a, P. Verhoeve^a, A. Peacock^a
a Astrophysics Division, Space Science Dept. of the European Space Agency, ESTEC, P.O. Box 299, 2200 AG Noordwijk, The Netherlands
^b School of Chemistry and Physics, Dept. of Physics, Lancaster University, Lancaster LA1 4YB, U.K.

One of the factors that limits the energy resolution of superconducting tunnel junctions (STJs) as photon detectors is the spatial dependence of the response on the photo-absorption site. To assess the role of spatial inhomogeneities we have analyzed quasiparticle diffusion processes in detail and developed a general analytical theory to describe the evolution of the quasiparticle density in an STJ. This theory accounts for (weak) non-linearity due to quasiparticle recombination, and includes the effects due to multiple quasiparticle tunneling, phonon coupling between the electrodes, diffusive losses into electrical connections and localised traps and losses at the edges. The theory does not require any assumptions about symmetry between base and counter electrode. We have derived an analytical model of the STJ response surface and the corresponding signal lineshape, which allows the influence of the above features to be treated independently. We discuss two examples in which this model is applied to experimental datasets obtained with multiple STJs, and demonstrate how this model can be used to obtain a thorough understanding of the factors that limit the energy resolution in STJs as photon detectors.

A10. Numerical Calculations of Diffusion Effects in STJ-Detectors

V.A. Andrianov^a, V.P. Gorkov^b
aInstitute of Nuclear Physics, Lomonosov Moscow State University, 119899 Moscow, Russia
^bThe Faculty of Computational Mathematics and Cybernetics, Lomonosov Moscow State University, 119899 Moscow, Russia

The numerical methods on the basis of grid functions are developed to describe the effects of diffusion of nonequilibrium quasiparticles in electrodes of STJ detectors. In addition to [1,2] numerical methods allow to describe quasiparticle motion in the electrodes of arbitrary shape with nonuniform boundary conditions. Besides different parameters of diffusion for upper and lower electrode are possible. Densities of quasiparticles in the upper and lower electrodes (n1 (x, y, t) and n2(x, y, t)) were described by a pair of the bound differential equations of Rothwarf-Taylor type (x, y are the coordinates in the plane of electrodes, t - time). The boundary and initial conditions used in the calculations were similar to those used in [1,2]. The model calculations were carried out for STJs of rhombus geometry.The pulse height spectra of the detector for electrodes with different ratio of diagonals of a rhombus were calculated. The influence of current leads and nonuniform boundary conditions were considered. The comparison of calculated spectra and experimental data was carried out. [1] O.J. Luiten, van den Berg et al., Proc.7th Int. Workshop on Low Temp. Detectors (LTD-7), ed. by S. Cooper, Munich 1997, p. 25. [2] L. Parlato, G. Ammendola et al., Nucl. Instr. Meth. A 444 (2000) 15.

A11. Fluctuations of Multitunneling in STJ Detectors

Victor V. Samedov
Moscow State Engineering Physics Institute (Technical University), 31, Kashirskoye Sh., 115409, Moscow, Russia

The theory of branching cascade processes is applied to the process of multitunneling in superconducting tunnel junctions (STJs). It is taken into account, that the process of signal formation includes multitunneling both of quasielectrons and holes. The model which takes into account the influence of the coupling of the quasielectron and phonon subsystems on multitunneling is also examined. This model takes into account the process of 2/Delta-phonon formation in recombination of two quasielectrons into a Cooper pair, 2/Delta-phonon propagation through an insulating layer, and subsequent breaking up of a Cooper pair in an opposite electrode. This process of 2/Delta-phonon transition through an insulating barrier does not transfer a charge, but contributes to the fluctuation of quasiparticle multitunneling. The probability generating functions for these processes are found. By means of probability generating functions it is possible to get expressions for the moments of distribution function of the number of quasiparticle tunnelings. In particular, the expressions for the mean number of quasiparticles multitunneling and its relative variances are obtained. In special case these expressions are reduced to expressions obtained in [1,2]. 1. D.J. Goldie et al., Appl. Phys. Lett. 64, 1994, p. 3169. 2. V. V. Samedov. Nucl. Instr. and Methods in Phys. Res., A444, 2000, p. 59.

A12. Fluctuations of STJ-Detector Signal due to Competition of Electron and Hole Tunneling Channels

V.A. Andrianov^a Victor V. Samedov^b,
^a Institute of Nuclear Physics, Lomonosov Moscow State University, 119899 Moscow, Russia
^b Moscow State Engineering Physics Institute (Technical University), 31, Kashirskoye Sh., 115409, Moscow, Russia

Statistical fluctuations of a STJ-detector collected charge under conditions of multiple tunneling of nonequilibrium quasiparticles and presence of electron and hole tunneling channels were considered. The behaviour of nonequilibrium quasiparticles in each electrode of STJ was characterised by three parameters: probabilities of tunneling by the electron channel P_e and by hole channel P_h and probability of losses P_loss. Using mathematical methods of generating functions, the expressions for mean value and relative variance of an collected charge are obtained. In a limiting case of one tunneling channel (P_h=0) the obtained expressions coincide with expressions deduced in [1]. The model calculations of signal fluctuations for asymmetric STJ-detector (Delta₁>Delta₂) as a function of bias voltage V_b were carried out. It was shown, that at voltages V_b<=(Delta₁-Delta₂)/e there is a noticeable increase of signal fluctuations due to adding the hole channel of tunneling. The minimum level of tunnel noise corresponds to high voltages V_b>(Delta₁-Delta₂)/e. 1. D.J. Goldie et al., Appl. Phys. Lett. 64, 1994, p. 3169

A13. Self-heating phenomena in superconducting tunnelling junctions

^aA.G.Kozorezov, ^bJ.K.Wigmore,A.Peacock⁺, Roland den Hartog⁺, G.Brammertz⁺ , D.Martin⁺, P.Verhoeve⁺, N.Rando⁺.
^aDepartment of Physics, Lancaster University, Lancaster, UK
^b+Astrophysics Division, European Space Agency - ESTEC, Noordwijk, Netherlands

Multiple tunnelling small gap structures are considered as an important contender for future optical photon detectors for astronomical applications. Recent experiments prove that in such STJs there occur important self-heating effects, significantly affecting their performance [1-3].
We have developed a kinetic theory of anomalous sub-gap currents in small gap multiple tunnelling STJs.
In the operating device the quasiparticle and phonon distributions are strongly non-equilibrium (non-thermalized). We predict a new class of phenomena resulting in a wealth of sub-gap current structure due to quasiparticle energy accumulation in the tunnelling - back tunnelling cycles. Among other features there occur the sub-gap current steps at voltages V=2Delta/en (n integer). We discuss the characteristics of non-equilibrium distribution of quasiparticle and phonons and show that the shape and magnitudes of steps on I-V curves as well as their dependence on bath temperature depend on junction parameters, including rates of quasiparticle tunnelling, recombination, residual losses and phonon escape from the junction. We discuss and compare the main predictions of the theory to the available experimental data. % ---------------------------------------------------------------- References 1. {A.Poelaert,A.G.Kozorezov, et.al., PRL, 82, 1257 (1999)} 2. {A.G.Kozorezov,J.K.Wigmore, et.al., APL, to appear, June (2001)} 3. {C.M.Wilson, L.Frunzio,D.E.Prober, Submitted to PRL (2001)}

A14. Vortex trapping in superconducting tunnel junction detectors

M. Ohkubo, K. Suzuki, K. Tanabe, H. Pressler, and M. Ukibe
Photonics Research Institute, National Institute of Advanced Industrial Science and Technology

Superconducting tunnel junction photon detectors, which exhibit high performance in the range between infrared and soft x-rays, are sensitive to vortices trapped in the superconducting thin films. The vortices cause the instability in detector operation and a large reduction in the signal height of detector response to photon absorption. Vortex trapping easily occurs when a residual magnetic field is present. We have investigated the details of the dependence of vortex trapping patterns on the strength of magnetic field perpendicular to the junction surface by using a scanning SQUID microscope, which enables the visualization of individual vortices, in niobium-based tunnel junctions. It has been found that the vortices are not trapped near junction edges, which can be the cause of spatial inhomogeneity of the signal height, and that there is a lower limit for vortex trapping. These experimental results may be explained by image and Meissner forces. The present results are very important for a magnetic shield design in practical applications.

A15. Strong quasiparticle trapping in a 6x6 array of Vanadium-Aluminium Superconducting Tunnel Junctions

G. Brammertz^a, A. Peacock^a, P. Verhoeve^a, A. Kozorezov^b, R. den Hartog^a, N. Rando^a, R. Venn^c
a Astrophysics Division, Space Science Department, ESA/ESTEC, P.O. Box 299, 2200AG Noordwijk, The Netherlands
^b School of Physics and Chemistry, University of Lancaster, Lancaster LA1 4YB, United Kingdom
^c Cambridge MicroFab Ltd., Trollheim Cranes Lane, Kingston, Cambridge CB3 7NJ, United Kingdom

A 6x6 array of symmetrical V/Al/AlOx/Al/V Superconducting Tunnel Junctions (STJs) was fabricated. The base electrode is a high quality epitaxial film with a residual resistance ratio (RRR) of 31. The top film is polycrystalline with an RRR of ~ 8. The leakage currents of the junctions are of the order of 0.5 pA/mm² at a bias voltage of 100 mV, which corresponds to a dynamical resistance of ~ 3 10⁵ ohm. When the array was illuminated by 6 keV X-ray photons from a Fe55 radioactive source the single photon charge output was found to be low and strongly dependent on the temperature of the devices. This temperature dependence at X-ray energies can be explained by the existence of a very large number of quasiparticle traps in the Vanadium. Quasiparticles are confined in these traps, having a lower energy gap than the surrounding material, and are therefore not available for tunnelling. The number and depth of these traps can be derived from the temperature dependence of the responsivity of the devices, (charge output per electron volt of photon input energy).

A16. Linearity investigations and pulse shape analysis of high resolution STJ X-ray detectors

M. Huber^a, G. Angloher^b, F. v. Feilitzsch^a, T. Jagemann^a, J. Jochum^a, T. Lachenmaier^a, J.-C. Lanfranchi^a, W. Potzel^a, A. Rüdig^a, J. Schnagl^a, M. Stark^a, H. Wulandari^a
aPhysik-Department E15, Technische Universität München, Munich, Germany
^bPhysik-Department E15, Technische Universität München, Munich, Germany. Current address: Oxford University, Oxford, GB

Al/Al_XO_Y/Al superconducting tunnel junctions (Al-STJs) on massive Si substrates were used as X-ray detectors. A low but detectable deviation from linearity was measured in the energy range between E = 1.74 keV and E = 6.49 keV. The nonlinearity can be explained by the escape of recombination phonons into the substrate. Varying the size of the Al-STJs shows that the nonlinearity is caused after the diffusive propagation of the quasiparticles over the STJs' electrodes. Possible "hot spot" effects could not be observed. By pulse shape analysis of the signals of Al-STJs a special event class is identified which is characterised by the distribution of the X-ray energy on the two electrodes. With these events the range of photoelectrons and Auger-electrons in the Al electrodes is estimated by MC-simulation. For a high resolution X-ray detector system based on an Al-STJ with a Pb absorber film located on a 100 nm thin Si₃N₄ membrane, pulse shape analysis allows to discriminate X-ray absorption in the Pb absorber and in the Al-STJ.

A17. Thermodynamical Model of Magnetic Calorimeters

A. Fleischmann^a, T. Danijarov^a, R. Weis^a, C. Enss^a, Y.H. Huang^b, and G.M. Seidel^b,
^aKirchhoff-Institut fuer Physik, Universität Heidelberg, D-69120 Heidelberg, Germany
^bDepartment of Physics, Brown University, Rhode Island, USA

X-ray detectors based on the concept of metallic magnetic calorimetry are well suited for high resolution spectroscopy. With prototype detectors, an energy resolution of 12 eV has been achieved. Magnetic calorimeters used for the detection of x-rays consist of a metallic paramagnetic temperature sensor, which is in good thermal contact with a suitable absorber. The sensor is placed in a small magnetic field, resulting in a magnetization roughly proportional to 1/T. Monitoring the magnetization with a low noise DC-SQUID makes the sensor a high resolution thermometer, which in turn makes the calorimeter highly sensitive to the deposition of energy. We present a model allowing for the calculation of the thermodynamic properties of the calorimeter. Within this model the parameters for optimizing the detector performance are derived. In addition, we discuss the fundamental sources of noise and the intrinsic limitation of the energy resolution of magnetic calorimeters.

A18. Thermalization of Magnetic Calorimeters

C. Enss^a, A. Fleischmann^a, T. Görlach^a, Y.H Kim^b, G.M. Seidel^b, H. Braun^c
aKirchhoff-Institut fuer Physik, Universität Heidelberg, D-69120 Heidelberg, Germany
^bDepartment of Physics, Brown University, Providence, RI 02912 USA
^cLehrstuhl für Experimentalphysik V, Universität Bayreuth, D-95440 Bayreuth, Germany

Calorimetric particle detectors based on metallic paramagnetic temperature sensors have show to be well suited devices for high resolution particle spectroscopy. Most of the work on metallic magnetic calorimeters was done using dilute alloys of erbium in gold as sensor material. In the temperature range of interest, the thermodynamic properties of erbium ions in gold all well understood, making the signal size as a function of temperature, magnetic field and concentration predictable. However, at temperatures below 50 mK the signal response of the calorimeter shows two relaxation times for the signal decay. Measurements of these time constants and the fractional amplitudes as a function of temperature and field indicate the presence of an additional thermodynamic system within the sensor material. Heat capacity measurements at temperatures as low as 100 µK suggest, that this additional contribution is arising from the quadrupole splitting of the Au nuclei (I=3/2) in the electric field gradients introduced by the presence of the Er ions. Measurements using calorimeters based on silver-erbium sensors support this assumption. In these measurements the additional, fast relaxation process was not observed. The host material silver (I=1/2) does not have a nuclear electric quadrupole moment. We discuss the origin of the two thermalization times of Au:Er-calorimeters and present the measurements on Ag:Er.

A19. Electron-phonon relaxation in hot-electron detectors below 1 K

Boris S. Karasik, Jet Propulsion Laboratory, California Institute of Technology Andrew V. Sergeev, Wayne State University Michael E. Gershenson, Rutgers University

Recently proposed submillimeter hot-electron direct detectors rely on the thermal coupling between electrons and phonons. Their sensitivity can be greatly enhanced if the coupling is made very weak. According to the theory, use of impure films should allow to achieve this goal. So far, the experimental situation has been somewhat confusing about this issue. A number of works have shown a cubic temperature dependence of the electron-phonon relaxation rate below 1 K. A conventional explanation is that this dependence is caused by direct interaction between electrons and phonons. We show that in most of these studies the pure limit was not reached. In this case, the electron scattering from vibrating impurities/boundaries dominates. The electron-phonon scattering rate varies from T⁴ × l for ql ll 1 to T² / l for 1 ll ql < 2(u_l / u_t)³ ~ 20-40 (u_l and u_t are the longitudinal and transversal sound velocities). In a wide temperature range around T ~ u_t/l the relaxation rate should have a T³ temperature dependence along with a weak l-dependence. Our recent experimental data for W and Ti films are in good agreement with the discussed interaction mechanism. The measured electron-phonon relaxation time followed the T^-4 dependence and was a record-long (25 ms) at 40 mK.

A20. Design and tests of high sensitivity NTD thermometers for the Planck-HFI instrument

M. Piat J.P. Torre J.M. Lamarre J.W. Beeman B. Leriche J.P. Crussaire F. Langlet.

The ESA satellite project Planck is dedicated to survey the sky and particularly the Cosmological Microwave Background at sub-millimeter and millimeter wavelengths. To perform this goal, the High Frequency Instrument (HFI) will use 48 bolometers cooled at 100mK by an open loop space qualified 3He/4He dilution cooler. The high sensitivity of the Planck-HFI instrument requires a challenging 100mK stability of 20nK.Hz^-0.5 down to 0.016Hz. In order to reach this requirement, a combination of a passive temperature filter with some active regulation stages is needed. High sensitivity thermometers will therefore be used for temperature stability monitoring but also for regulation. In order to optimise the design of such thermometers, we have modelled low temperature semiconducting thermometers by using a semi-analytical approach of Anderson insulators, taking into account both the electrical field and the electron/phonon decoupling effects. This leads to choose a convenient NTD Ge material with an optimal size bigger than usual. The first measurements of such devices showed important decoupling effect due to Kapitza resistance with the mounting. Nevertheless, a sensitivity of about 8nK.Hz^-0.5 down to 0.1Hz was obtained, limited at lower frequencies by the thermal fluctuations of our test bed. Recent results on these devices will be presented.

A21. Non-ideal effects in doped semiconductor thermistors

M. Galeazzi ^a, D. Liu ^a, D. McCammon ^a, W. T. Sanders ^a, P. Tan ^a, K.R. Boyce ^b, R. Brekosky ^b, J.D. Gygax ^b, R. Kelley ^b, D.B. Mott ^b, F. S. Porter ^b, C. K. Stahle ^b, C.M. Stahle ^b, and A. E. Szymkowiak ^b
aUniversity of Wisconsin, Madison, WI 53706 USA
^bNASA/Goddard Space Flight Center, Greenbelt, MD 20771 USA

Semiconductor thermistors have been used for several years and their ideal behavior is well known experimentally and theoretically. Their current performance is limited by non-ideal behaviors. These include 1/f noise and non-ohmic effects. We find that the 1/f noise appears to be a 2D effect, and can be greatly reduced by fabricating thicker thermistors. Eliminating this noise could improve the intrinsic detector resolution as much as 40%. It also allows us to study other sources of excess noise. The non-ohmic behavior can be empirically explained using a hot-electron model. Although this model seems not suitable for semiconductors in the variable range-hopping regime, where the electrons are localized, it fits well the experimental data. We measured an excess white noise at low frequencies consistent with the predicted thermodynamic fluctuations between electrons and phonons. We also measured a characteristic time of the non-ohmic behavior that is consistent with a C/G time constant in the hot electron model. Both results support the physical validity of the hot electron model. To optimize the performances of the next generation of detectors, we implemented the non-ideal behaviors in a model to predict the expected total noise and energy resolution. The comparison between the model and real data from the XQC and XRS experiments shows good agreement.

A22. Hot electron model in doped silicon thermistors

D. Liu ^a, M. Galeazzi ^a, D. McCammon ^a, W. T. Sanders ^a, B. Smith ^a, P. Tan ^a, K.R. Boyce ^b, R. Brekosky ^b, J.D. Gygax ^b, R. Kelley ^b, D.B. Mott ^b, F. S. Porter ^b, C. K. Stahle ^b, C.M. Stahle ^b, and A. E. Szymkowiak ^b
aUniversity of Wisconsin, Madison, WI 53706 USA
^bNASA/Goddard Space Flight Center, Greenbelt, MD 20771 USA

Non-ohmic behavior of doped silicon and germanium can be empirically explained using a hot-electron model, which is motivated by the hot electron effect in metals at low temperatures. This model assumes that the thermal coupling between electrons and lattice at low temperatures is weaker than the coupling between electrons, so that the electric power applied to the electrons raises them to a higher temperature than the lattice. Although this model seems not suitable for semiconductors in the variable range-hopping regime, where the electrons are localized, it fits quite well the experimental data. To determine whether the hot electron model in doped semiconductor is just an alternative way to parameterize the data or has some physical validity, we investigated the noise and frequency-dependence of the impedance of doped silicon thermistors that are used for low temperature thermal X-ray detectors. The measured excess white noise at low frequencies is consistent with the predicted thermodynamic fluctuations of energy between electron and phonon systems. The non-ohmic behavior shows a characteristic time that can be interpreted as a C/G time constant in the hot electron model. This is consistent with the assumption of a hot electron system thermally separated from the lattice system.

A23. 1/f Noise in Ion-Implanted Silicon Thermistors

D. McCammon ^a, M. Galeazzi ^a, D. Liu ^a, W. T. Sanders ^a, P. Tan ^a, K.R. Boyce ^b, R. Brekosky ^b, J.D. Gygax ^b, R. Kelley ^b, D.B. Mott ^b, F. S. Porter ^b, C. K. Stahle ^b, C.M. Stahle ^b, and A. E. Szymkowiak ^b
aUniversity of Wisconsin, Madison, WI 53706 USA
^bNASA/Goddard Space Flight Center, Greenbelt, MD 20771 USA

We have characterized the 1/f noise in standard ion-implanted silicon thermistors, which are about 250 nm thick. We find that it is associated with the bulk of the implant, and is interpretable as a dR/R fluctuation that is independent of the bias and depends only on the doping density and resistivity, or electron temperature. This excess noise is large enough that it has a significant effect on the energy resolution or NEP of a detector using these thermistors. The very steep temperature dependence of the 1/f noise suggested that it might be related to the conduction becoming two-dimensional, and we have fabricated thicker detectors to test this hypothesis. Similar doped silicon thermistors that are 1500 nm thick show negligible 1/f noise, but otherwise behave identically to the thinner thermistors of the same volume. This simple change could provide a 40% improvement in resolution for some existing X-ray detectors.

A24. Performance Modeling of Micro-calorimeter Detectors

M. Galeazzi ^a, D. Liu ^a, D. McCammon ^a, W. T. Sanders ^a, P. Tan ^a, E. Figueroa-Feliciano ^b, and C. K. Stahle ^b
aUniversity of Wisconsin, Madison, WI 53705 USA
^bNASA/Goddard Space Flight Center, Greenbelt, MD 20771 USA

In order to optimize the design of micro-calorimeters and bolometers, it is necessary to be able to predict the resolution of any given configuration. For detectors using ion-implanted silicon thermistors, we have sufficient engineering data on their non-ideal characteristics to predict the noise contributions from all currently known sources, given the basic physical parameters of the thermometer. We have constructed an analytical detector model that incorporates terms for thermistor Johnson and 1/f noise, amplifier noise, load resistor Johnson noise, and thermodynamic fluctuations between the electron and phonon systems in the thermometer as well as between the absorber, the thermistor, and the heat sink. The model has been checked by comparing its predictions to data obtained from existing detectors developed for the XRS spectrometer on Astro-E and for the XQC sounding rocket program. We are now using our model to optimize designs for new detectors employing thick implants that greatly reduce the 1/f noise term.

A25. Measurement of anomalous resistance-temperature relation for neutron transmutation doped germanium

A. L. Woodcraft^a, R. V. Sudiwala^b.
^a Department of Physics and Astronomy, University of Wales, Cardiff, 5, The Parade, Cardiff. CF24 3YB.

We present precise measurements of the resistance-temperature variation of several samples of neutron transmutation doped (NTD) germanium, at temperatures from 100~mK to 1~K. This material is used widely both for thermometry and for the thermistor element in bolometers and microcalorimeters. The resistance is generally found to follow the variable range hopping equation R(T)=R₀exp(T₀/T)ⁿ, where R₀ and T₀ are material parameters. A value of n=0.5 is supported by theory, and usually appears to allow good fits to data. However, we find that setting n=0.5 produces clear systematic errors for some of our samples. Taking n as a fitting parameter gives excellent fits over a large temperature range with n=0.53 and n=0.56 for different samples. We consider possible causes for this behaviour, and suggest that in general NTD germanium calibration data should be examined carefully for errors caused by assuming an incorrect value of n.

A26. High Performance Semiconductor-Based Bolometers

S. H. Moseley^a, D. McCammon^b
aILaboratory for Astronomy and Solar Physics, NASA/GSFC
^bUniversity of Wisconsin

Recent experiments on diffused thermometers in SOI material show great promise, having significantly less 1/f noise than their implanted counterparts. This lower noise promises better resolution for energy detectors, and offers a path to improved far infrared bolometers. Here, we present a design for infrared detectors based on micromachined structures using diffused SOI thermometers. Based on the measured thermometer properties, we show that these devices can offer significant performance improvements over the present generation of semiconductor-based bolometers in response time, sensitivity, and ease of production.

A27. The Suitability of Sapphire for Large Area Calorimeters

Y.H. Kim^a, H. Eguchi^a, C. Enss^b, A. Fleischmann^b, Y.H. Huang^a, R.E. Lanou^a, H.J. Maris^a, A.N. Mosharnuck^a, G.M. Seidel^a, B. Sethumadhavan^a, and W. Yao^a
aDepartment of Physics, Brown University, Providence, RI 02912, USA
^bKirchhoff-Institut für Physik, Universität Heidelberg, D-69120 Heidelberg, Germany

Large wafers having an area of at least 100~cm², to serve as calorimeters, are required in a proposed detector of low energy solar neutrinos using liquid helium below 50~mK as the target material. The calorimeters must have a threshold energy below 16~eV to be able to detect single photons of the UV scintillation from helium. In the development of such calorimeters we have investigated the properties of sapphire and the thermal coupling of sapphire to a sensor in the temperature range from 30 to 100~mK. Energy is deposited in a 1~cm³ sapphire crystal by an x-ray and the resulting response of a magnetic sensor is monitored. The sensor is a 40 micron diameter piece of erbium doped gold, the temperature- dependent magnetization of which is measured using a SQUID. Thermal contact between the sapphire and sensor is made through an Au film. The magnitude and response time of the signal are found to depend upon the properties of the gold film, in particular its thickness. The rise and decay times of the signal provide information on the thermalization processes involving the athermal phonons. The return of the calorimeter to thermal equilibrium appears, in part, to be influenced by the presence of two-level tunneling systems in the sapphire.

A28. A Constant Temperature TES Micro-calorimeter with an External Electronic Feedback System

N. Moeckel ^a, M. Galeazzi ^a, Mark Lindeman ^b, and C. K. Stahle ^b
aUniversity of Wisconsin, Madison, WI 53706 USA
^bNASA/Goddard Space Flight Center, Greenbelt, MD 20771 USA

One major problem with TES micro-calorimeters is the very narrow temperature range in which they work. To detect high energy events the heat capacity of the detector must be sufficiently big to avoid running the sensor outside its sensitivity region. The bigger heat capacity limits the best energy resolution that can be obtained. One way to avoid a saturation effect keeping the heat capacity small is to run the detector at constant temperature reducing the power dissipated into it by an amount equal to the power conducted into the thermometer from the energy deposition. We studied the possibility of such a detector using an external electronic feedback system that reduces the bias voltage on the sensor. Using a traditional electro-thermal feedback to run a constant temperature detector, the signal amplitude can be reduced, but the noise of the readout electronics does not change and this may worsen the energy resolution. Moreover the gain of the feedback, determined by the sensitivity alpha may not be big enough to keep the temperature constant. With an external feedback, the noise of the readout electronics is reduced proportionally to the signal and the feedback gain can be much bigger. In this paper we outline the characteristics of such a system, we study its optimization and we investigate its performances.

A29. Materials Considerations in the Operation of Geometrically-metastable Superconducting Detectors

M.R. Gomes^a, TA Girard^a, P.Valko^a,
^aCentro de F�sica Nuclear,Universidade de Lisboa 1649-003 Lisbon, Portugal

Investigations of the signal response of a variety of superconducting, of both Type I and II, are reported. The results are interpreted in terms of the flux motion sensitivity of the fast-pulse acquisition electronic readout, and suitability for use in geometrically-metastable devices indicated.

A30. Response Dynamics of Geometrically-metastable Superconducting Detectors under Irradiation

TA Girard^a, M.R. Gomes^a, P.Valko^a,
^aCentro de F�sica Nuclear,Universidade de Lisboa 1649-003 Lisbon, Portugal

We report investigations of the response of geometrically-metastable superconducting devices under irradiation, demonstrating that the behavior differs significantly from that under normal variation of external magnetic field at constant temperature. The results are interpreted within the context of hotspot formation and the "explosive nucleation" model of Shapiro, and the possible relationship between measurements and the Kibble-Zurek mechanism indicated.

A31. Weakly expressed effects in HTS detected by a single-layer flat coil-based Tunnel Diode oscillator technique demonstrating its wide possibilities for high-resolution detection

S.G. Gevorgyan^a,b, T. Kiss^a, T. Nishizaki^c, H.G. Shirinyan^b, A.A. MovsisyanV^b, V.S. Gevorgyan^b, M. Inoue^a, T. Harayama^a, T. Matsushita^a, N. Kobayashi^c, and M. Takeo^a
a Graduate School of ISEE, Kyushu University, Fukuoka, 812-8581, Japan
^b Institute for Physical Research, National Academy of Sciences, Ashtarak, 378410, Armenia
^c Institute for Materials Research, Tohoku University, Sendai, 980-8577, Japan

We developed flat coil-based TD-oscillator technique for high-resolution tests of penetration depth of MHz-range magnetic field and detection of absorption inside HTS. The method is based on simultaneous detection of the inductance and Q-factor changes of single-layer coil, which leads to frequency and amplitude changes of the oscillator. It enables detecting the changes ~ 10^-12H of film's magnetic inductance (changes ~1 Angstrom of penetration depth). It detects also the changes ~ 10^-9W of testing field's power absorption by a film, originated from variation of its internal flux distribution. It operates in high magnetic fields, measures in wide dynamic ranges of testing parameters, and is sensitive especially near T_c. These allow revealing of fine peculiarities of superconductive transition and flux flow in plate-like HTS at beginning of "Cooper" pairs' formation. We detected new "paramagnetic" peculiarity on temperature-transition curves of HTS and LTS materials before their diamagnetic repulsion. We revealed an anomalous absorption of testing field's power by HTS film close to end of its magnetic-transition. Simultaneous frequency and amplitude tests enabled also constructing the vortex magnetic phase diagram in HTS. What is important, the method enables all above in small-volume films and crystals without disturbing them near T_c, and during the simple measurement.

A32. NIS Tunnel Junction Detector with Segmented Absorbers

F. Yoshihara^a, I. Kanno^a, M. Katagiri^b, M. Ukibe^c, M. Ohkubo^c
aKyoto University, Sakyo, Kyoto 606-8501, Japan
^bJapan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195, Japan
^cNational Institute of Advanced Industrial Science and Technology, Tsukuba,Ibaraki, 305-8568, Japan

An NIS tunnel junction detector is a calorimeter, which energy resolution is proportional to the square root of the heat capacity of the normal metal absorber. It is not possible to enlarge the absorber area of this detector without deteriorating the energy resolution, in general. In this paper, we suggest a method to enlarge the absorber area of an NIS tunnel junction detector without deteriorating its energy resolution: we divide the absorber area into several parts and connect them by superconductor leads. The heat capacity of each segmented absorber remains small, but the summed area of absorbers is large. By applying this method, we estimated better energy resolution in case of dividing absorber into segments, comparing to the one-body absorber with the same area. Considering the case dividing the absorber into two, the heat capacity of each segmented absorber becomes a half, its heat response becomes twice as fast in case its tunnel current is the same. Moreover, one may have detectors with thicker absorbers, which is sensitive to higher energy X-rays, with dividing the normal metal into some segments and keeping the heat capacity small. So far, we fabricate an NIS tunnel junction detector by dc magnetron sputtering. Each layer pattern was defined by using shadow mask. We measured I-V characteristics of the detector at 270mK.

B01. Physics and Applications of Normal-Insulator-Superconductor Tunnel Junctions

J. N. Ullom^a,
^aLawrence Livermore Laboratory, Livermore, CA

In this talk, the physics and applications of Normal-Insulator-Superconductor (NIS) tunnel junctions will be reviewed. The current-voltage properties of NIS junctions are diode-like with a strong temperature dependence. Hence, these structures can be used as sensitive thermometers at temperatures well below the energy gap, delta, of the superconducting electrode. Calorimeters and bolometers for the detection of X-rays and millimeter-wave radiation, respectively, have successfully been built from NIS junctions. For junction voltages comparable to delta/e, current flow removes energy from the normal electrode. This property has been exploited to build microrefrigerators capable of cooling thin-film circuits from 0.3 K to temperatures near 0.1 K. Recent efforts to increase the size of these refrigerators and prospects for their integration with other low-temperature electronics will be discussed. Finally, it has been demonstrated that structures built from two NIS junctions in series can act as superconducting three-terminal devices. Recent results from these devices will also be described. This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract No. W-7405-ENG-48.

B02. Annular Superconducting Tunnel Junction Detectors: experimental results under X-ray illumination

L. Frunzio^a,c, L.Li^a, D.E. Prober^a, I. Vernik^b, M. Lissitski^c,d, C. Nappi^c, R. Cristiano^c
aDepartment of Applied Physics and Physics, Yale University, P.O. Box 208284, New Haven, CT 06520-8284, USA
^bHypres Inc., 175 Clearbrook Rd., Elmsford, NY 10523, USA
^cIstituto di Cibernetica "E. Caianiello", Via Campi Flegrei 34, I-80078 Pozzuoli, Napoli, Italy and INFN Sezione di Napoli
^dINFM Sezione di Napoli

We report on the first experiment detecting 55Fe X-ray photons by an annular Superconducting Tunnel Junction (STJ) detector. The experiments have been performed on Nb/Al-AlOx/Nb annular STJ detectors fabricated at HYPRES Inc. The radiation, impinging on an STJ detector, breaks Cooper pairs and creates excess quasiparticles. They are collected and counted by tunneling in order to measure the incoming energy. The stability of the bias point of the detector has been obtained in two different configuration. In the first one, as usual, we applied, an external magnetic field parallel to the barrier to suppress the STJ critical current and resonances. In the second configuration, we trapped a single fluxon through the anular structure in the STJ barrier during the transition to the superconducting state. This is the innovative configuration which allows to obtain the same suppression without any externally applied parallel magnetic field. In both configurations we observed current pulses produced by the interaction of the STJ electrodes with single X-ray photons and they appear to be identical.

B03. Energy, position and time resolving photon spectrometers with Ta-based STJ devices

Ph. Lerch, E. C. Kirk, J. Olsen, A. Mchedlischvili, A. Zehnder H. R. Ott ^a
Paul Scherrer Institute CH - 5232 Villigen, Switzerland
^a ETH - Hönggerberg, CH - 8093 Zürich, Switzerland

We are developing superconducting tunneling junction (STJ) devices as photon counting imagers. In an attempt to increase the number of pixels and the collection area without increasing the complexity of the wiring in the same proportion we suggest to use a distributed readout scheme. A Ta absorber strip is readout by 2 STJs placed at both ends. Our devices are made out of 8 strips and 16 STJs. Their readout will thus require 16 channels for an effective area of 64 pixels. We compare the behavior of Ta/Al₁/AlO_x/Al₂/Nb devices with results obtained from numerical simulations of the proximity effect. We have performed irradiation experiments on single strips with visible and soft x-ray photons. The effects of the absorber/trap interface and the thickness of the Al trapping layer on the charge collection are presently investigated and shall be presented.

B04. Single Photon 1-D Imaging X-ray Spectrometers using Superconducting Tunnel Junctions

L. Li, L. Frunzio, C. Wilson, D. E. Prober
Yale University, New Haven, CT

We are developing superconducting, single photon, 1-D imaging x-ray detectors for applications in x-ray astronomy and astrophysics. The detectors use a Ta absorber and Al-AlOx-Al tunnel junctions for readout. Photons absorbed in the Ta create excess quasiparticles which are trapped in the Al tunnel junctions on each end of the absorber and cause an increase in their subgap current. The integrated charge is proportional to the photon energy. The charge division between the two junctions gives 1-D position information. Present devices have achieved an energy resolution of 13 eV FWHM for 6 keV x-rays over an 20 �m x 100 �m absorber area near the end of the absorber. The energy resolution is within a factor of two of the statistical limit. The broadening of the energy resolution in the center is caused by the niobium contact. A device with Ta ground contact to the trap of one junction instead of Nb in the center was tested. The energy resolution of this device is uniform over a large area in the center. We will discuss the performance and physics of these devices and scaling to larger absorber sizes with more pixels.

B05. Two-dimentional position resolution and correction on incidence position dependency of signal heights of series-junction detectors.

S. Kamihirata, M. Kurakado, A. Kagamihata, K. Hirota, H. Hashimoto and K. Taniguchi [a] H. Sato, Y. Takizawa, C. Otani and H. M. Shimizu [b] [a] Division of Electronics and Applied Physics, Osaka Electro-Communication University [b] RIKEN (The Institute of Physical and Chemical Research)

Superconducting tunnel junction (STJ) detectors have the possibility of ultrahigh energy resolution[1]. Series-junction consists of STJs connected in series. The series-junction detector absorbs incident energy of a radiation in the single-crystal substrate[2]. The energy of radiation is converted to non-thermal phonons[1].The detection efficiencies of the superconducting series-junction detectors are much higher than those of superconducting single junction detectors. Present series-junction detector has four series-junctions on a surface of the substrate. We can obtain two-dimensional position resolution by making use of the heights of signal from the four series-junctions. Total signal heights depend on the incidence position in the series-junction detector. We developed a method to correct the incidence position dependency of pulse height. Correction factors were determined for each incidence region, making use of the position resolution, and thereafter pulse heights of signals were modified by the correction factors. By means of measurements of radiations, i.e., X-rays and ��-particles, and through simulations of radiation detection, it was confirmed that the correction of the incidence position dependency by the method is useful to improve the energy resolutions of the series-junction detectors. References [1] M. Kurakado, Nucl. Instrum. Methods 196, 275 (1982) [2] M. Kurakado, X-Ray Spectrometry, 29, 137 (2000)

B06. Ta Superconducting Tunnel Junctions fabrication process for photon counting detectors

Philippe Feautrier Laboratoire d'AstrOphysique de Grenoble, 414 rue de la piscine, Domaine Universitaire, 38040 Grenoble Cedex 9, France Jean-Claude Villegier CEA-Grenoble SPSMS/LCP, F38054 Grenoble Cedex 9, France Corentin Jorel Laboratoire d'AstrOphysique de Grenoble, 414 rue de la piscine, Domaine Universitaire, 38040 Grenoble Cedex 9, France Alain Benoit CRTBT, CNRS BP 166-38042 Grenoble Cedex 9, France. Bertrand Delaet LAOG \& CEA-G; present adress: JPL Jet Propulsion Laboratory California Institute of Technology M/S 168-314 4800 Oak Grove Drive Pasadena, CA 91109

The properties of Superconducting Tunnel Junctions (STJ) make them very suitable for low light level astronomical observations: they are able to count photons from the visible light to the near-infrared with a rather good energy resolution. We have developed a modified version of the "SNEP" fabrication process for making Ta/Al-AlOx-Al/Ta/Nb STJ's. These junctions show a very low sub-gap leakage current at 0.1 K. A double thin aluminum trapping layer and a Ta absorber grown epitaxially by magnetron sputtering on a R-plane sapphire substrate maintained at 600�C are achieved. High quality epitaxial tantalum films has been obtained with RRR = 30 and sharp X-Ray diffraction peaks. Some recent improvements in the fabrication process will be detailed. The experimental junction parameters will be analyzed: current density, subgap leakage current, Ta mean free path, barrier thickness and intrinsic junction capacitance. An optical set-up has been completed to achieve photon counting performances. An original, room temperature, charge sensitive preamplifier has been built for this purpose. Photon counting ability in the near infrared at 0.78 micron has been demonstrated with Nb junctions. First results with the new tantalum junctions will also be detailed.

B07. Aluminum Superconducting Tunnel Junction as X-Ray Detector: Technological Aspects and Phonon Decoupling from the Substrate

M. Lissitski^a,b, E. Esposito^a,c, L. Frunzio^a,f, D. Perez de Lara^a,c, R. Cristiano^a,c, G. Angloher^d, M. Salvato^e, G. Carbone^e, L.Li^f, D.E. Prober^f
aIstituto di Cibernetica "E. Caianiello", Via Campi Flegrei 34, I-80078 Pozzuoli, Napoli, Italy
^bINFM Sezione di Napoli
^cINFN Sezione di Napoli
^dTechnische Universitat Munchen, Physik Department E15, James-Franck-Str., D-85748 Garching, Germany
^eDipartimento di Fisica and INFM Universit� di Salerno, Via S. Allende, I-84081 Baronissi, Salerno, Italy
^fDepartment of Applied Physics and Physics, Yale University, P.O. Box 208284, New Haven, CT 06520-8284, USA

We have investigated Al/AlOx/Al Superconducting Tunnel Junctions (STJs) for their use as X-ray detector. The junctions have been fabricated on sapphire substrates, by using different underlayers (Nb, SiO) and barrier transparencies. It was found that the transparency and the quality of the AlOx tunnel barrier strongly depend on the microstructure of the Al base electrode (grain size, texture) which, in turn, is determined by the substrate/underlayer materials. The deposition parameters were optimized in order to fabricate junctions capable to resolve in energy the spectrum emitted by an 55Fe X-ray source. Experiments under X-ray irradiation on STJs with and without a SiO buffer layer are reported. The spectra show that the SiO layer succeeds in reducing the events coming from the phonons generated into the substrate. Besides, it is interesting to remark that the yield is about 85% for STJs with the buffer layer, quite high in comparison with the 5% of STJs without the buffer layer. Another feature is that the junction with the buffer layer shows one single peak instead of the four peaks corresponding to the two MnK lines of the 55Fe source for each electrode, as it was observed in a similar STJ without the SiO buffer layer.

B08. STJ X-Ray Detectors with Killed Electrode

V.A. Andrianov^a, P.N. Dmitriev^b, V.P. Koshelets^b, M.G. Kozin^a, I.L. Romashkina^a, S.A. Sergeev^a
aInst. of Nuclear Phys., Lomonosov Moscow State Univ., 119899 Moscow, Russia ^bInst. of Radio Engineering and Electronics RAS, 103907 Moscow, Russia

STJ detectors with killed electrode[1] have a number of potential advantages. They enable a) to cut substantially the signal from the killed electrode as compared with that from the main absorbing electrode, b) to reduce the tunneling noise, c) to reduce the influence of the boundary conditions due to decrease of the quasiparticle diffusion length. In the present work the junctions with Al/Nb/Al/AlO_x/Al/Nb/NbN layer sequence were studied. The base electrode was killed by adjacent to the substrate Al-layer. Pulse height spectra arising under STJ irradiation with X-rays from Fe-55 source were measured at T=1.35 K. Signal amplitude dependence on the bias voltage was studied. Various mechanisms of signal formation are considered. Insufficient attenuation of the signal from the killed electrode can be connected with the phonon exchange between electrodes. Variation of the spectra shape with detector area is in accord with quasiparticle diffusion model. [1] O.J. Luiten , van den Berg et al., Proc.7th Int. Workshop on Low Temp. Detectors (LTD-7), ed. by S. Cooper, Munich 1997, p. 25.

B09. Development of Superconducting Tunnel Junctions as an Energy-Dispersive Detector for EUV and UV Radiation

H. Sato, T. Ikeda, T. Oku, C. Otani, K Kawai, H. M. Shimizu, Y. Takizawa, H. Miyasaka, H. Watanabe
RIKEN (The Institute of Physical and Chemical Research), Wako, Japan

We are developing an energy-dispersive detector for EUV and UV radiation using superconducting tunnel junctions with Al trapping layers. We have evaluated the performance of the detector for EUV photons using the Synchrotron Facility (KEK-PF) at High Energy Accelerator Research Organization in Tsukuba.We have achieved the energy resolution of FWHM=18 eV (including the external noise of 17 eV) for 55 eV EUV photons with a 100 x 100 um² STJ. In this paper, we will present and discuss the details of the junction design,our experiments and the results.

B10. Once More on the Energy Resolution of STJ Detectors

Victor V. Samedov
Moscow State Engineering Physics Institute (Technical University), 31, Kashirskoye Sh., 115409, Moscow, Russia

The paper[1] presents an experiments with Ta based STJ (200 nm Ta/5 nm Al/1 nm AlOx/5 nm Al/30 nm Ta/20 nm NbN), which show measured energy resolutions of 4.6 eV, 8.1 eV and 20.5 eV at 525 eV, 1.5 keV and 6 keV respectively. This experimental data are analyzed on the basis of the expression for energy resolution obtained in [2]. In this report it is shown that after subtraction of the electronic noise from the energy resolution, it is necessary to plot the relative variance of output signal as a function of inverse number of quasielectrons created by incident photons. The interception of this linear dependence with the axis of ordinates gives the contribution to the broadening of the line caused by spatial fluctuation of the photon interaction point. This contribution to the energy resolution can be considered as the criterion of STJ quality and can be used for comparing STJs. The noticed discrepancies between the experimental data and the calculated energy resolution in [1] are explained by incorrect accounting for quasiparticle multitunneling. 1. G. Brammertz et al. Preprint ESLAB 2000/107/CA. 2. V. Samedov. Proc.7th Int. Workshop on Low Temp. Detectors (LTD-7), ed. by S. Cooper, Munich 1997, p. 29.

B11. Periodical distribution of charge output in superconducting tunnel junction having a structure of Nb/Al/AlOx/Al/Nb

T. Nakamura^a, M. Katagiri^a, M. Ohkubo^b, H. Pressler^b, H. Takahashi^c and M. Nakazawa^c
aJapan Atomic Energy Research Institute
^bNational Institute of Advanced Industrial Science and Technology
^cUniversity of Tokyo

Periodical distribution of charge output in superconducting tunnel junction (STJ) having a structure of Nb/Al/AlOx/Al/Nb with size of 200 x 200 um2 was first observed by Low Temperature Scanning Synchrotron Microscope experiments. Two swelled parts were appeared in the distribution of charge output and the period of the swelled parts was about 100um. It is found that this distribution was occurred under the conditions; (i) the size of the STJ is more than twice of Josephson characteristic length and (ii) a bias voltage applied to the device is more than 0.2mV of about the energy gap of the trapping layers. It was confirmed that this anomalous distribution of charge output significantly distorts the shape of the photo peak and degrades the energy resolution of the STJ detector.

B12. High counting rate X-ray detector using a superconducting tunnel junction with current readout method

M. Katagiri^a, T. Nakamura^a, M. Ohkubo^b, H. Pressler^b, H. Takahashi^c and M. Nakazawa^c
aJapan Atomic Energy Research Institute
^bNational Institute of Advanced Industrial Science and Technology
^cUniversity of Tokyo

We developed a high counting rate X-ray detector using a superconducting tunnel junction (STJ) having a structure of Nb/Al/AlOx/Al/Nb with a fast current readout system. The STJ has a current rise time of 100ns, a current decay time of 260nsec and resistance of 20ohm at 0.4K. A fast current readout system consists of a superconducting coil of about 1mH for current load, a fast current amplifier and a fast peak hold circuit. High counting rate characteristics of the X-ray detector are measured by synchrotron radiation. The energy resolution for counting rate between 10cps and 100kcps is about 270eV and the energy resolution for 300kcp is about 300eV at X-rays of 4keV. It is confirmed that this X-ray detector has an excellent performance for high counting rate X-ray detection.

B13. The response function of superconducting tunnel junction detectors

S. Friedrich^a, B. Beckhoff^b, M. Frank^a, R. Fliegauf^b, S. E. Labov^a, G. Ulm^b,
^aLawrence Livermore National Laboratory, L-418, Livermore, CA 94551, U.S.A.
^bPhysikalisch-Technische Bundesanstalt, Abbestrasse 2-12, 10587 Berlin, Germany

We have characterized the response function, the spectral artifacts and the absolute efficiency of superconducting tunnel junction (STJ) x-ray detectors using monochromatic synchrotron radiation. The experiments were performed at the plane grating monochromator beamlines for bending magnet and for undulator radiation in the PTB radiometry laboratory at the electron storage ring BESSY II. Both beamlines provide monochromatic radiation of high spectral purity. Two STJ detectors were characterized in the energy range from 100 eV to 1900 eV with respect to their energy resolution ranging from about 12 eV to 28 eV FWHM and their count-rate capability. We have investigated the spatial origins and spectral distribution of artifacts by systematically scanning a collimator across the detector area. In addition, we have determined the absolute detection efficiency of one STJ detector in special operation shifts of BESSY II by adapting the stored electron beam current to the count-rate capability of the STJ. We will present x-ray fluorescence spectra taken with STJ detectors at the ALS synchrotron, discuss the consequences of spectral artifacts for X-ray fluorescence analysis of dilute samples and propose some improvements for future detector lay-outs.

B14. Characterisation of Titanium films for low temperature detectors

E. Monticone^a, V. Lacquaniti^a, M. Rajteri^a, M. L. Rastello^a, C. Gandini^a, E. Pasca^b, G. Ventura^b,
^aIstituto Elettrotecnico Nazionale Galileo Ferraris, Torino, Italy
^bDept. of Physics, University of Florence, Florence, Italy

Transition edge sensors (TES) are promising devices as low temperature light detectors due to their high energy resolution and broadband response. One of the suitable materials for TES is titanium that shows transition temperatures up to 0.5 K. Titanium films have already been investigated by different authors, but the correlation between the electrical properties at different temperatures in the normal state and the transition temperatures is lacking. In this work we study Ti films, with thickness between 10 nm and 1000 nm, deposited by e-beam on silicon and silicon nitride. Critical temperatures and electrical resistivities of these films have been measured as function of thickness, deposition pressure, deposition rate and substrate temperature. The behaviour of the critical temperatures versus the residual resistivities is discussed in the frame of the Testardi and Mattheiss theory.

B15. Rectifying Characteristics of InSb Device at Low Temperature

I. Kanno^a, F. Yoshihara^a, O. Sugiura^b, M. Katagiri^c
aKyoto University, Sakyo, Kyoto 606-8501, Japan
^bTokyo Institute of Technology, Ookayama, Meguro, Tokyo 152-8552, Japan
^cJapan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195, Japan

McHarris predicted the possible high energy resolution of InSb semiconductor detector. InSb has the band gap of 0.165eV, and the mobilities of electrons and holes 78000 and 750cm²/(Vs), respectively. This band gap energy is less than 1/6 of that of Si, and gives the energy resolution of 60eV for 6keV X-rays, without taking the Fano factor into account. High atomic number and high density of InSb also make the detector more attractive. The impurity in InSb, however, makes its resistivity very small, even at low temperature. No successful attempt was reported on InSb as a high energy resolution detector so far. Infrared sensors and Hall devices have been the main application of InSb. We report here the rectifying characteristics of InSb device, at the temperature below 4.2K. The employed InSb was p-type one with Ge dopant of 3.5x10¹⁵cm^-3 concentration. The resistivity of the substrate was 0.29ɏcm at 77K. The Schottky elctrode was made by Al evaporation and Mo was deposited on Al to make better electric contact. The Ohmic contact was simply taken by soldering InSb wafer to Cu plate. This rectifying characteristics shows the possibility of InSb device as X-ray detector.

C01. Superconducting transition edge sensors for X-ray microcalorimetry

H.F.C. Hoevers, Space Research Organization Netherlands

The current work on superconducting Transition Edge Sensors (TESs) for X-ray microcalorimetry can be separated into the research involving the optimization of a single pixel detector and the development of an imaging array of microcalorimeters. The research is motivated by astronomical applications, such as Constellation-X or XEUS, and microanalysis. During the past years, research groups have achieved promising energy resolutions of 2 eV at 1.5 keV and 5 eV at 5.89 keV with single pixel microcalorimeters. The paper discusses the measured resolutions in relation with the noise levels and the theoretical predictions. The current performance of microcalorimeters and routes for further optimization of single pixel detectors are discussed, based on the physics involved. Recently, the development of imaging microcalorimeter arrays using TES microcalorimeters has started. The feasibility and expected performance of an imaging array is determined by the geometry of the array and the design of the individual pixels. Starting from the requirements for energy resolution, sensor speed, absorption efficiency and packing density the design of the individual pixels is discussed along with the expected performance of a complete array, including the issue of thermal and electrical crosstalk between pixels.

C02. Performance of X-ray microcalorimeters with an energy resolution below 4.5~eV and 100~µs response time

W.M. Bergmann Tiest^a, H.F.C. Hoevers^a, W.A. Mels^a, M. Ridder^a, M.P. Bruijn^a, P.A.J. de Korte^a, and M.E. Huber^b
aSpace Research Organization Netherlands,
Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
^bDepartment of Physics, University of Colorado at Denver
P. O. Box 173364, Denver, CO 80217-3364, USA

The performance of X-ray microcalorimeters with different geometries, and under different illumination conditions, has been investigated. These microcalorimeters consist of a TiAu Transition Edge Sensor (TES) and a Cu absorber. With these microcalorimeters we regularly achieve energy resolutions below 4.5 eV FWHM for 5.89 keV X-rays in combination with a response time of about 100 µs. The measured energy resolution is analysed and discussed based on current-voltage characteristics and noise spectra. The variation in geometry did not influence the detector performance to a large extend, and spatial non-uniformities are considered to be small. In order to increase the absorption efficiency and packing density (mushroom-shaped) Bi absorbers are being produced and tested with our microcalorimeters. In addition, the performance of several digital filtering schemes is investigated using both experimental as well as simulated data.

C03. Performance of Mo/Au TES microcalorimeters

Mark A. Lindeman, Regis P. Brekosky, Enectali Figueroa-Feliciano, Fred M. Finkbeiner, Mary Li, Caroline K. Stahle, Carl M. Stahle, Nilesh Tralshawala (NASA GSFC)

We are developing X-ray calorimeters to meet the specifications of the Constellation-X mission. Each calorimeter consists of a transition-edge-sensor (TES) thermometer, which is suspended on a silicon-nitride membrane. Our TES thermometers are Mo/Au bilayer films that are biased in the sharp phase transition between the superconducting and normal-metal states. These calorimeters have demonstrated very good energy resolutions: 2.4 eV at 1.5 keV and 3.7 eV at 3.3 keV. The energy resolutions are limited by thermal noise and Johnson noise (which are intrinsic to any resistive calorimeter) plus excess noise. The excess noise, which is several times larger than the Johnson noise, is consistent with frequency-independent voltage noise in the TES. Detailed measurements of one Mo/Au TES demonstrate that the excess noise is independent of the voltage applied to the TES over a range of biases at the same TES resistance. The magnitude of the excess noise is smallest at the high-resistance end of the phase transition. We also compared noise in square Mo/Au TES's ranging in size from 150 microns to 600 microns to learn how the excess noise is affected by the geometry of the TES.

C04. Fabrication of bridge-type microcalorimeter arrays with Ti-Au Transition-edge-sensors

M. Ukibe^a, T. Kimura^b, T. Nagaoka^b, H. Pressler^a, M. Ohkubo^a,etc.
^aNational Institute of Advanced Industrial Science and Technology, 1-1-1, Umezono Tsukuba, Ibaraki 305-8568 JAPAN
^bUniversity of Meiji, 1-1-1 Higashisanda Tama-ku Kawasaki, Kanagawa 214-8571 JAPAN

The present stage of the cryogenic detectors is in the development of arrays. The arrays of TES microcalorimeters have generally been fabricated on SiN_X membrane structure. In conventional membrane structure fabricated by backside etching, it is difficult to realize arrays having a mechanical toughness and a large filling factor. It is possible to overcome the difficulty by using a bridge-type membrane structure, of which SiN_X membranes are floating with a gap of 10-50 µm on Si substrates. For checking etching and other processes, we have fabricated a small scale array with the bridge-type membrane structure. The preliminary version of the TES microcalorimeter array has a dimension of 10 x 6 mm² and 5 x 5 pixels. Each pixel consists of a 0.7 mm x 2 mm SiN_X membrane with a thickness of 1 µm and a Ti/Au bilayer TES of 0.5 x 0.5 mm². This array has a filling factor of about 0.1. However, it is possible to obtain a high filling factor by changing a mask design or attaching mushroom-shaped absorbers.

C05. The Constellation-X Focal Plane Microcalorimeter Array: An NTD-Germanium Solution

J. Beeman(a), E. Silver(b), S. Bandlerb(b), H. Schnopper(b), S. Murray(b), N. Madden(a), D. Landis(a), E. E. Haller(a), and M. Barbera(c) (a)Lawrence Berkeley National Laboratory (b)Harvard-Smithsonian Center For Astrophysics (c)Osservatorio Astronomico G.S. Vaiana

The hallmarks of Neutron Transmutation Doped (NTD) Germanium cryogenic thermistors include high reliability, reproducibility, and long term stability of bulk carrier transport properties. The dopant concentration in this material is easily controlled by adjusting the exposure time of the germanium to a known neutron fluence. Since the neutron absorption cross section in germanium is relatively small, the resulting dopant distribution in this material is extremely uniform. This uniformity is especially important when building large area arrays. Using micro-machined NTD Ge thermistors with integral "flying" leads, we can now fabricate two-dimensional arrays that are built up from a series of stacked linear arrays. We believe that this modular approach of building, assembling, and perhaps replacing individual modules of detectors is essential to the successful fabrication and testing of large multi-element instruments. Details of construction are presented.

C06. Fabrication of Close-packed TES Microcalorimeter Arrays Using Superconducting Molybdenum/Gold Transition-Edge Sensors

F. M. Finkbeiner^a,b, R. P. Brekosky^a,c, J. A. Chervenak^a, E. Figueroa-Feliciano^a,d, M. J. Li^a,e, M. A. Lindeman^a,f, N. Tralshawala^a,e, C. K. Stahle^a, C. M. Stahle^a
aNASA/Goddard Space Flight Center, Greenbelt, MD 20771
^bDepartment of Astronomy, University of Maryland
^cSwales Corporation, Beltsville, MD
^dPhysics Department, Stanford University
^eRaytheon ITSS, Lanham, MD
^fNAS/NRC Resident Research Associate

We present an overview of our efforts in fabricating TES microcalorimeter arrays for use in astronomical x-ray spectroscopy. Two distinct types of array schemes are currently pursued: A 5x5 single pixel TES array, where each pixel is a TES microcalorimeter, and the position-sensitive TES (PoST) array. In the latter, a row of 15 thermally-linked absorber pixels is read out by two transition-edge sensors (TES) at its ends. Both schemes employ 150x150 square micron large superconducting Mo/Au bilayers as the TES which are produced by electron-beam deposition under ultra-high vacuum conditions. The TES are placed on silicon nitride membranes for thermal isolation from the structural frame. The silicon nitride membranes are prepared by a state-of-the-art Deep Reactive Ion Etch process into a silicon wafer before or after the TES deposition. The absorbers are 2 to 10 microns thick bismuth layers thermally deposited onto the TES or onto a patterned gold film in the case of the PoST array. In order to closely pack the arrays without decreasing its structural and functional integrity, we have already produced arrays of cantilevered pixel-sized absorbers and slit membranes. Furthermore, we have started to investigate ultra-low resistance through-wafer micro-vias to bring the electrical contact out to the back of a wafer.

C07. Detailed characterization of Mo/Au TES microcalorimeters

Mark A. Lindeman, Regis P. Brekosky, Enectali Figueroa-Feliciano, Fred M. Finkbeiner, Mary Li, Caroline K. Stahle, Carl M. Stahle, Nilesh Tralshawala (NASA GSFC)

We are optimizing Mo/Au transition-edge-sensor (TES) calorimeters to meet the specifications of NASA's Constellation-X mission. Our calorimeters have already demonstrated very good energy resolution of X rays (2.4 eV at 1.5 keV). We wish to further improve the energy resolution by reducing excess noise in the calorimeters. Development of a detailed model and understanding of the noise is instrumental to reaching this goal. Towards that end, we employ a linear model that describes the response of a calorimeter to signal and various sources of noise. The model is based on detailed measurements of the parameters that affect the calorimeter's performance, such as current-voltage characteristics of the TES, thermal conductance of our silicon-nitride membranes, and inductance in the electronic circuit used to bias the TES. We determine the sharpness of the superconducting phase transition by fitting the model to the measured responsivity of the calorimeter. The model relates sources of noise, such as phonon noise, Johnson noise, and hypothetical sources of excess noise, to measurements of noise in the TES. Based on this analysis, we find that the excess noise is consistent with frequency-independent voltage noise in the TES.

C08. Arraying Compact Pixels of Transition-edge Microcalorimeters for Imaging X-ray Spectroscopy

C. K. Stahle, M. A. Lindeman, E. Figueroa-Feliciano, M. J. Li, N. Tralshawala, F. M. Finkbeiner, R. P. Brekosky, J. A. Chervenak
NASA Goddard Space Flight Center, Greenbelt, MD 20771 USA

We are developing superconducting transition-edge sensor (TES) based x-ray microcalorimeters for astronomical x-ray spectroscopy. We have obtained very high energy resolution (2.4 eV at 1.5 keV and 3.7 eV at 3.3 keV) in large, isolated TES pixels using Mo/Au proximity-effect bilayers on silicon nitride membranes several mm wide. In order to be truly suitable for use behind an x-ray telescope, however, such devices need to be arrayed with a pixel size and focal-plane coverage matched to the telescope focal length and spatial resolution. For the Constellation-X mission, this requires fitting the TES, its thermal link, and contact wiring into a 0.25 mm square, a far more compact geometry than has previously been investigated. We have demonstrated that the weak link can be restricted to a narrow (~10 micron) perimeter of membrane around the TES and still provide a thermal conductance in the acceptable range. Varying the size and placement of slits in that nitride perimeter, we can tune that value. We are also investigating the impact of restricting the sensor area to a 0.15 mm square. We will present the results of these characterizations and the spectral performance of individual devices.

C09. Fabrication of TES X-Ray Detector Arrays

Deiker, S., Bergren, N., Hilton, G., Irwin, K., Nam, S.W., Rudman, R., Wollman, D., NIST-Boulder

Transition Edge Sensor (TES) microcalorimeters have demonstrated record-breaking energy resolution over a large range of energies (2 eV at 1.5 keV, 4.5 eV at 6 keV), and because of their low impedance couple well to SQUID amplifiers. These factors make them ideal candidates for the large format detector arrays needed in both imaging x-ray astronomy missions and high count-rate materials microanalysis applications. NIST is fabricating multiple pixel arrays of transition edge sensor (TES) microcalorimeter detectors with these uses in mind. With the eventual goal of large, close-packed arrays, we have begun with small (2x2) arrays to investigate the fabrication and operation challenges involved. Our latest fabrication techniques and results will be presented.

C10. Development of high resolution X-ray detectors using tungsten phase transition thermometers (SPT)

G. Angloher¹, A. Bento¹, H. Kraus¹, F. Pröbst², W. Seidel^{2 1}University of Oxford, Department of Physics, Keble Road, Oxford OX1 3RH, UK ²Max-Planck-Institut fuer Physik, F�hringer Ring 6, 80805 M�nchen, Germany

The next generation of X-ray detectors in astrophysics is required to exhibit high resolving power over >mm2 detector areas. This can be achieved with tungsten as thermometer material as its bulk transition temperature is as low as 15 mK. We investigate detector designs where superconducting and normal conducting absorbers are read out by tungsten-SPTs. In addition, we deposit tungsten films on a range of substrates and by varying the growth conditions we can choose the transition temperature of the W-SPTs between 15 mK and 65 mK. This may be of interest for applications where an operating temperature as low as 15mK is impractical. Sharp phase transitions are obtained with tungsten grown on epitactic Al2O3, and also on amorphous buffer layers of Si3N4, SiO2 and Al2O3. This allows testing of various detector geometries and absorber coupling schemes (use of membranes, electron or phonon coupling, etc). So far, an energy resolution of Delta E = 60 eV (E = 5.9 keV) is achieved for a lead absorber of 1 mm diameter and 6 microns thickness.

C11. Status of X-ray Microcalorimeter Development at ISAS

R. Fujimoto^a, K. Mitsuda^a, N. Iyomoto^a, M. D. Audley^a, T. Miyazaki^a, T. Oshima^a, M. Yamazaki^a, K. Futamoto^a, Y. Takei^a, Y. Ishisaki^b, T. Kagei^b, T. Hiroike^b, T. Ohashi^b, N. Y. Yamasaki^b, A. Kushino^b, H. Kudo^c, H. Sato^c, T. Nakamura^c, E. Goto^c, S. Shoji^c, T. Homma^c, T. Osaka^c, Y. Kuroda^d, M. Onishi^d, M. Goto^d
aInstitute of Space and Astronautical Science, Sagamihara, Japan
^bTokyo Metropolitan University, Hachioji, Japan
^cWaseda University, Tokyo, Japan
^dMitsubishi Heavy Industries, Nagoya, Japan

At ISAS/TMU/Waseda, we are developing a superconducting phase-transition microcalorimeter array for the next Japanese X-ray astronomy satellite. Our goal is to achieve an energy resolution of ~ 3~eV, and imaging capability with a large covering area, using ~ 30× 30 pixels. In our design, a thin-film Ti-Au bilayer is fabricated on a thermally isolated silicon pixel, and an absorber with a large covering factor is attached on it. The readouts of a large-format array are multiplexed either in the time domain or in the frequency domain. So far, we glued a tin film as an absorber, operated at 100--200~mK, and achieved the energy resolution of 100~eV (FWHM) at 5.9~keV. We are now working on a calorimeter with a new design, where an absorber is electrodeposited on the silicon pixel. As readouts of our calorimeter system, a SQUID array amplifier and a 4-input SQUID array amplifier are used. Both achieve low readout noise. The latter is a device that has recently been developed for multiplexing calorimeter signals. In this presentation, we summarize the outline of our development, and report the performance of our new calorimeter system. The details of the fabrication processes, and the multiplexing technique in the frequency domain are presented in separate papers.

C12. Fabrication of an x-ray microcalorimeter with an electrodeposited x-ray microabsorber

H. Kudo^a, H. Sato^a, T. Nakamura^a, E. Goto^a, S. Shoji^a, T. Homma^a, T. Osaka^a, K. Mitsuda^b, R. Fujimoto^b, N. Iyomoto^b, M. D. Audley^b, T. Miyazaki^b, T. Oshima^b, M. Yamazaki^b, K. Futamoto^b, Y. Takei^b, Y. Ishisaki^c, T. Kagei^c, T. Hiroike^c, T. Ohashi^c, N. Y. Yamasaki^c, A. Kushino^c Y. Kuroda^d, M. Onishi^d, M. Goto^d
aWaseda University, Tokyo Japan
^bInstitute of Space and Astronautical Science, Sagamihara, Japan
^cTokyo Metropolitan University, Hachioji, Japan
^dMitsubishi Heavy Industries, Nagoya, Japan

A superconducting phase-transition microcalorimeter is a promising detector for high resolution X-ray spectroscopy. For the astronomical use, a large format array (~1000 pixels) is now strongly requested. We are studying micromachining process to achieve such a large format array. In our process, the absorber is fabricated as a so-called `mushroom' shape by electrodeposition, to attain a high covering fraction. In our design, the calorimeter pixel of 1 mm x 1 mm is supported by a fine long silicon beam. First, a 200 um thick silicon wafer is processed from the surface by reactive ion etching (RIE). After patterning a temperature sensor (TES) on the silicon pixel, a sacrificial photoresist structure is fabricated. It consists of two layers, a negative photoresist as a mold of the supporting point of the absorber, and a thick positive photoresist as a mold of the absorber. Then, the tin absorber is fabricated by electrodeposition. To obtain good purity and uniformity of tin, the optimized condition was chosen using the SnSO4 and H2SO4 bath with additives of cresol sulfonic acid and polyethylenglycol (PEG). The absorber is then polished by CMP (chemical mechanical polishing), and finally the wafer is etched by RIE from the back side to produce the pixel and the beam. We will present our fabrication process and the results in detail.

C13. First Results from a Position-Sensing TES Imaging Calorimeter

E. Figueroa-Feliciano^1,2, J. Chervenak¹ F. M. Finkbeiner^1,3, M. Li^1,4, M. A. Lindeman^1,5, C. K. Stahle¹, C. M. Stahle¹ , N. Tralshawala^1,4
1NASA Goddard Space Flight Center, Greenbelt, MD 20771 USA
²Stanford University, Department of Physics, Stanford, CA 94305 USA
³University of Maryland, Department of Astronomy, College Park, MD 20742 USA
⁴Raytheon ITSS, Lanham, MD 20706 USA
⁵NAS/NRC Resident Research Associate

We are developing a high energy resolution, imaging spectrometer called a Position Sensing Transition Edge Sensor (PoST). A PoST is a calorimeter consisting of two Transition Edge Sensors (TESs) on the ends of a long absorber to do one dimensional imaging spectroscopy. Comparing rise time and energy information, the position of the event in the PoST is determined. Energy is inferred from the sum of the two pulses. We have fabricated 7, 15, and 32 pixel PoSTs using our Mo-Au TESs on a silicon nitride suppot structure. We show our first results from this promising technology, where we have successfully read out 7 pixels with two TESs and achieved a resolution of 30 eV at 1.5 keV. We also discuss the theoretical limits for the resolution of these devices.

C14. Integrated Focal Plane Arrays for Millimeter-wave Astrophysics

J. Bock^a, A. Goldin^a, C. Hunt^b, A. Lange^b, H. LeDuc^a, J. Zmuidzinas^b,
^aJet Propulsion Laboratory, Pasadena, CA
^bCalifornia Institute of Technology, Pasadena, CA

We are developing focal plane arrays of bolometric detectors for sub-millimeter and millimeter-wave astrophysics. We propose a flexible array architecture using arrays of slot antennae coupled via low-loss superconducting Nb tranmission line to microstrip filters and antenna-coupled bolometers. By combining imaging and filtering functions with tranmission line, we are able to realize unique architectures such as a multi-band polarimeter and a planar, dispersive spectrometer. Micro-strip bolometers have significantly smaller active volume than standard detectors with extended absorbers, and can realize higher sensitivity and speed of response. The integrated array has natural immunity to stray infrared radiation or spectral leaks, and minimizes the suspended mass operating at 0.1 - 0.3 K. Calculations and performance of the slot antennae and filtering is presented in a parallel poster presentation. We discuss development of an instrument that realizes the planar spectrometer concept in waveguide. We also describe future space-borne spectroscopy and polarimetery applications.

C15. Focal Plane Arrays of Voltage-Biased Superconducting Bolometers

Michael J. Myers^a, John Clarke^a, J. M. Gildemeister^a, Adrian T. Lee^a, P. L. Richards^a, Dan Schwan^a, J. T. Skidmore^a, Helmuth Spieler^b, Jongsoo Yoon^a
aDepartment of Physics, University of California at Berkeley
^bPhysics Division, Lawrence Berkeley National Laboratory

The 200µm to 3mm wavelength range has great astronomical and cosmological significance. Science goals include characterization of the cosmic microwave background, measurement of the Sunyaev-Zel'dovich effect in galaxy clusters, and observations of forming galaxies. Cryogenic bolometers are the most sensitive broadband detectors in this frequency range and the development of large arrays will be critical for future science progress. We report on two types of voltage-biased superconducting bolometer arrays being developed by our group. We have developed an absorber coupled bolometer suitable for large-format filled arrays. This detector is produced on a silicon nitride suspension using standard planar lithography. We have produced a 1024 element array of fully released and suspended 1.5mm x 1.5mm nitride micro-meshes with a filling factor of 88%. We also built and tested a voltage-biased superconducting bolometer on a similar nitride micromesh as a prototype for one array element. Our group is also developing planar antenna coupled bolometers. Antenna coupled detectors do not require horns and the band defining filters can be fabricated in superconducting microstrip on the same substrate as the bolometer. This highly integrated design should facilitate scaling to a very high pixel count. We will report on our current progress in the fabrication and testing of these devices.

C16. SAMBA: Superconducting Antenna-coupled, Multi-frequency, Bolometric Array.

Alexey Goldin^a,c, James J. Bock^a, Cyntia Hunt^a Andrew E. Lang^b, Henry Leduc^a Tasos Vayonakis^b Jonas Zmuidzinas^b
a JPL
^b California Institute of Technology ^c NRC fellow

We present a design for multipixel, multiband submillimeter instrument: SAMBA (Superconducting Antenna-coupled, Multi-frequency, Bolometric Array). Unlike traditional designs like SCUBA and BOLOCAM, SAMBA uses slot antenna coupled bolometers and microstrip filters. The concept allows for a much more compact, multiband imager compared to a comparable feedhorn-coupled bolometric system. The concept has some advantages compared to horn coupled bolometric systems. SAMBA incorporates array of slot antennas, superconducting transmission lines, wide band multiplexor and superconducting transition edge bolometers. The transition-edge film measures the millimeter-wave power deposited in the resistor that terminates the tranmission line. By combining imaging and filtering functions with tranmission line, we are able to realize unique architectures such as a multi-band polarimeter, which are discussed in parallel oral presentation. We present a numerical analysis of the wide-band microstrip filters and the slot antenna array.

C17. Transition Edge Sensor Bolometers for Submillimeter Astronomy

J. A. Chervenak^a, D. Benford^a, T. Chen^a, B. DiCamillo^a, R. Shafer^a, J. Staguhn^a, S. H. Moseley^a, K. D. Irwin^b, S. W. Nam^b, N. Bergren^b, John M. Martinis^b E. N. Grossman^b, C. D.Reintsema^b, T. E. Harvey^b,
^aNASA Goddard Space Flight Center, Greenbelt, MD
^bNIST, Boulder, CO

We describe our effort to fabricate and test transition edge sensor bolometers (TESs) that are suitable for sub-millimeter and millimeter astronomy. In particular, we are exploring the integration of a robust low T_c TES bilayer process with low thermal conductance structures for both filled focal plane arrays and feedhorn-coupled arrays. A comparison of our fabrication methods for Mo/Au and Mo/Cu bilayers will be presented.

C18. Superconductive Hot-Electron Direct Detectors for Submillimeter Space Telescopes

Boris S. Karasik, Bertrand Delaet, and William R. McGrath Jet Propulsion Laboratory, California Institute of Technology Michael E. Gershenson Rutgers University Andrew V. Sergeev Wayne State University

We develop a hot-electron direct detector (HEDD) capable of counting single millimeter-wave photons. Such a detector will meet the needs of future space far-infrared missions and can be used for background-limited detector arrays on future space telescopes. The HEDD is based on a microbridge (1-�m-size) transition edge sensor fabricated from an ultra-thin film of a superconductor with T_c = 0.1-0.3 K. A very strong temperature dependence of the electron-phonon coupling in superconductors with small electron-mean-free-path allows to adjust the electron-phonon scattering time to the desired value. The Nb contacts block the thermal diffusion of hot carriers out of the bridge because of the Andreev reflection. The measurements of the electron-phonon relaxation time in hafnium and titanium have demonstrated that the bolometer response time of ~ 1 ms at T = 0.1 K is possible without using any high-thermal-resistance suspension of the detector. For a device with lateral dimensions 1x1 �m², this would result in a NEP = 10^-20 W/sqrt(Hz). The frequency response of the prototype antenna-coupled devices have been measured to be flat over the range 250-1000 GHz. First test results of a multiplexing scheme based on the Hadamard Transform encoding and using a single SQUID amplifier will be discussed.

C19. Development of high-resolution gamma-ray spectrometers

A. Loshak^a, D.T. Chow^a,b, M.F. Cunningham^a,b, O. Drury^a,b, M.L. van den Berg^a, J.N.Ullom^a, T.W. Barbee Jr.^a, M. Frank^a, S.E. Labov^a
aLawrence Livermore National Laboratory, Livermore, CA, 94550
^bDepartment of Applied Science, University of California, Davis

We are developing arrays of gamma-ray microcalorimeters based on a Mo/Cu multilayer superconducting transition edge sensor (TES) thermally coupled to a bulk absorber. Our goal is to build a high resolution and good quantum efficiency gamma-ray spectrometer in the energy range of 60 keV-200 keV. This energy range is particularly interesting for nuclear weapons materials inspection and measurement of nuclear reaction cross-sections for U and Pu. We need to achieve better than DeltaE/E<=10^-3 relative energy resolution which is more than a factor of 4 better than theoretical resolution of modern Ge detectors. Previously, using electrothermal feedback, we have achieved energy resolution of 70 eV FWHM for 60 keV gamma-rays using 1 mm² × 0.25 mm Sn absorber which had 70% absorption efficiency at 60 keV. In order to linearize the response of the detector and extend the detection energy range we have implemented an external active feedback bias circuit. Here we describe recent results from single-pixel detectors and discuss future plans. This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract No. W-7405-ENG-48.

C20. Mo/Au microcalorimeters

J. E. Olsen ^a, E. C. Kirk ^a, Ph. Lerch ^a, A. Zehnder ^a, H. R. Ott ^b, M. Huber ^c, G. C. Hilton ^c, J. M. Martinis ^c
aPaul Scherrer Institute CH - 5232 Villigen, Switzerland
^b ETH - Hönggerberg, CH - 8093 Zürich, Switzerland
^b NIST, 80303 Boulder, CO, USA

We fabricated Mo/Au bilayers on silicon nitride membranes as transition edge sensors (TES). The critical temperature of the bilayers is adjusted, by proximity effect, to be around 100 mK. TES devices are mounted on the cold stage of a dilution refrigerator and are voltage biased with the use of thin film Au shunts. The input coil of a one stage series array of {em dc} SQUIDs, kept at 2.2 K, is connected in series with the device. Results on 6 keV irradiation experiments will be presented.

C21. Mo-Cu bilayers as Transition Edge Sensors for X-ray astrophysics

P. Tan, L. D. Cooley, M. Galeazzi, D. Liu, D. McCammon, K. L. Nelms, and W. T. Sanders
University of Wisconsin, Madison, WI 53706 USA

We are developing Transition Edge Sensor (TES) thermometers for X-ray astrophysics applications. We are using Mo-Cu bilayers to obtain a working temperature around 60 mK. It is known that the shape of the device edges affects the transition properties. We have developed a process for undercutting the top Cu layer that appears to adequately control the edge effect. Since we plan to fly these detectors in a magnetic refrigerator, we studied the effect of small magnetic fields on the bilayer transition. We are also studying the effect of the bias power density on the sensitivity and excess noise of the TES.

C22. Development of the X-ray microcalorimeter with a superconductive Ir layer

M. Ohno*a, Y. Noguchi*a, D. Fukuda*a, H. Takahashi*b, M. Nakazawa*a, M. Ataka*c, M. Ukibe,*d, F. Hirayama*d, M. Ohkubo*d *a Department of Quantum Eng. and System Sci., The University of Tokyo,Tokyo *b RACE, The University of Tokyo,Tokyo *c Institute of Industrial Science, The University of Tokyo,Tokyo *d National Institute of Advanced Industrial Science and Technology, Ibaraki

We are developing an Ir TES X-ray microcalorimeter. Ir has good properties such as chemical stability and low Tc of 112mK, therefore by using Ir TES we can expect good quality of high energy resolution X-ray detector. First we fabricated Ir film of 0.5mmX0.5mm using a dc magnetron sputtering with heating and then the film is etched to form a TES by a reactive ion etching method. The weak thermal link to the heat sink is created by fabricating the Ir TES on a silicon nitride membrane. Our TES sensor is voltage biased with an on-chip shunt resistor, and current is measured by a dc-SQUID array. The measured energy resolution was 194eV for 5.9keV X-ray but this value is extremely worse than a theoretical resolution. We think the curent limitation in energy resolutuion of our Ir TES arises from non-uniformity in thermalization process. Thermalization process in Ir is relatively slow as compared with other materials therefore the localization in electrothermal feed-back and resulting fluctuation in temperature might propagate through the sensor. To improve the thermalization property of TES device, now we are trying to employ a new geometry that has shorter length of electrodes and some thin slits that separate the thermalization area of the Ir TES device.

C23. TES x-ray microcalorimeters with single element superconductors

D. Fukuda^a, Y. Noguchi^a, H. Takahashi^b, M. Ohno^a M. Ataka^c, M. Ukibe^d, F. Hirayama^d, M. Ohkubo^d, M. Nakazawa^a.
^aDep. of Quantum Eng. and Systems Sci., The University of Tokyo, Tokyo.
^bRACE, The University of Tokyo, Tokyo.
^cInstitute of Industrial Science, The University of Tokyo, Tokyo.
^dNational Institute of Advanced Industrial Science and Technology, Ibaraki.

In chemical state microanalysis with PIXE spectrometry, it is necessary to employ detectors with high-energy resolution, large detection efficiency and high counting rate. We are now developing TES x-ray microcalorimeters using single element superconductor for this application. One of the adavantages of the single superconductor TES is its very stable and reproducible property because of no inter-diffusion process and simple structure compared to the bilayered TES. Tungsten and Iridium are promising superconducting elements because they have very low T_c that is necessary to achieve a high-energy resolution detector. Prototype TES microcalorimeters were fabricated with these films and the x-ray responses are measured. Observed signals with a W-TES are saturated for 5.9keV x-ray energy because of the small heat capacity of our device, however, we have obtained the energy spectrum by integrating the current changes of the signal. The currently achieved energy resolution with this method is 37eV (FWHM) @ 5.9keV. We have observed excess noise from the x-ray measurement with the TES of a large detection area. We think the noise comes from non-uniform response depending on the position of the TES where x-rays are absorbed because of the slow thermalization property. We will present these results and discuss the characteristics of the single superconducting TES microcalorimeters.

C24. Development of a distributed read-out imaging TES X-ray microcalorimeter

S. Trowell A. D. Holland G.W.F. Fraser University of Leicester, University Road, Leicester, LE1 7RH, UK D. Goldie Oxford Instruments Scientific Research Division, Newton House, Cambridge Business Park, Cowley Road, Cambridge, CB4 4WZ, UK

The requirement for high resolution imaging X-ray spectroscopy for astrophysics is well documented. We report on the development of a linear absorber detector for one-dimensional imaging spectroscopy, read-out by two Transition Edge Sensors (TESs). The current design, details of which are discussed, incorporates a composite gold/bismuth absorber to maximise the thermal conductivity for a given heat capacity. The TESs used are based on a single layer of iridium and have been developed under our single pixel microcalorimeter programme. These demonstrate stable and controllable superconducting-to-normal transitions in the region of 100 mK. Results from Monte Carlo simulations are presented indicating that the device configuration is capable of detecting photon positions to better than 200 microns, thereby meeting the spatial resolution specification for missions such as XEUS of ~250 microns.

D01. Photon counting detectors for the far infrared

O. Astafiev, V. Antonov, T. Kutsuwa and S. Komiyama
Department of Basic Science, University of Tokyo
Japan Science and Technology Corporation (JST)

We study quantum dots (QDs) as photon detectors of the far-infrared (FIR). The QDs are formed by laterally confining two-dimensional electron gas (2DEG) by negatively biased metal gates, which are deposited on the top of GaAs/Al_xGa_1-xAs heterstructures with the high mobility 2DEG. Transport through the QDs is measured in the single electron transistor (SET) regime at temperature of 70 mK. Two mechanisms of the photo-excitations are explored: (i) inter Landau level photo-excitation in high magnetic fields (B = 3.4 - 4.15 T) and (ii) collective plasma excitations at a characteristic frequency of the parabolic bare confinement potential. The single photon counting is achieved by the QDs in high magnetic fields at nearly cyclotron frequencies in a wavelength range 0.17 mm < lambda < 0.21 mm. Oppositely, in the second mechanism, double-QDs are studied in the absence of magnetic fields. With these double-QDs, the high sensitive detection approaching to the single photon detection level is realized at wavelength of 0.6 mm.

D02. Radio-Frequency Single-Electron Transistors Readouts for UV thru Submillimeter Single-Photon Counters

R.J. Schoelkopf^a, K. Segall^a, J.D. Teufel^a, and K. Aidala^a T.R. Stevenson^b, C.M. Stahle^b, and S.H. Moseley^b, A. Aasime^c, P. Wahlgren^c, and P. Delsing^c.
^aYale University, New Haven, CT
^bNASA/Goddard Space Flight Center, Greenbelt, MD
^cChalmers University of Technology, Goteborg, Sweden

We describe progress on the use of Radio-Frequency Single-Electron Transistors (RF-SETs) as high-performance readout amplifiers for cryogenic single-photon detectors based on superconducting tunnel junctions (STJs). The high charge sensitivity and large bandwidth of the RF-SET, along with low power dissipation, low capacitance and on-chip integrability make it a good candidate for high impedance detectors. We recently demonstrated an RF-SET with a voltage noise of 25 nV/rt(Hz), configured as a transimpedance amplifier in a charge-locked loop feedback configuration with a bandwidth of about 100 kHz. The initial performance is sufficient to readout single-photon pulses from UV/optical STJ detectors at their intrinsic energy sensitivities. A proof-of-concept demonstration of wavelength-division multiplexing of the RF-SET amplifiers has also been performed. Finally, we will describe preliminary results on very high-sensitivity direct detectors (SQPCs) for the submillimeter waveband. This device, essentially an antenna-coupled STJ, offers the possibility of true single-photon counting for milli-eV photons. Dark current measurements of prototype devices suggest that noise-equivalent powers of 10^-18 Watts/rt(Hz) or better could be attained at 250 mK. Predicted sensitivities for an optimized device could approach {10^-20} Watts/rt(Hz), and would be background-limited for even the most demanding applications in space astrophysics.

D03. Superconducting electronic device with transistor-like properties

N.E. Booth^a, L. Parlato^b, G.P. Pepe^c, G. Ammendola^c, E. Esposito^d, G. Peluso^c, A. Barone^c and R. Scaldaferri^c
aDepartment of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK
^bDip. Ingegneria dell'Informazione, Via Roma 16, Aversa (CE), Italy
^cDip. Scienze Fisiche, I.N.F.M., Universita di Napoli Federico II, I-80125 Naples, Italy
^dIstituto di Cibernetica del C.N.R., Via Toiano 6, Arco Felice (NA), Naples, Italy

Particle and photon detectors based both on superconducting tunnel junctions and on superconducting transition edge sensors are becoming widely used. A superconducting transistor with large current gain and bandwidth that can operate in close proximity to the detectors could open up new possibilities. Recently the Naples-Oxford collaboration has fabricated and tested a three-terminal superconducting device with transistor-like properties at an operating temperature of 4.2 K. It consists of a stacked double tunnel junction structure where the intermediate film is a bilayer of superconducting Nb and an Al quasiparticle trap which can work either in the superconducting or in the normal metal state. Current amplification factors of more than 50 are observed at 4.2 K when the Al is in the normal state. The device also has power gain of more than 1000 and a high degree of unidirectionality. The results can be explained on the basis of the recently proposed QUAsiparticle TRApping TRANsistor, which should have wide applications in detection systems operating at low temperatures. Results of device design studies will also be presented.

D04. Electron Multiplier with a Cascade of NIS Tunnel Junctions

V.S. Shpinel, V.A. Andrianov
Institute of Nuclear Physics, Lomonosov Moscow State University, 119899 Moscow, Russia

It is shown that in a cryogenic detector with hot electron microcalorimeter a signal can be recorded and amplified by a device which consists of a series of normal metal-insulator-superconductor (NIS) tunnel junctions. In the sequence S₀N₁IS₁N₂IS₂�N_nIS_nN_n+1, the normal metal N acts as a microcalorimeter and simultaneously plays a role of tunnel junction normal electrode. Absorption of the energy E in an absorber S₀ gives rise to production of hot electrons in the microcalorimeter SN₁S and to increase of the tunnel current through the first and next NIS junctions. Each transfer of an electron through the tunnel barrier to the neighboring microcalorimeter brings the energy ~Delta and raises its electron temperature. Thus the proposed structure has the properties of electron multiplier. The temperature rise in each SN microcalorimeter is a solution of the system of differential equations. Model calculations of a signal of this device were carried out for a wide range of physical parameters. Signal amplification by means of two NIS junctions in series was mentioned in [1]. The same principle of amplification was put forward and tested in [2]. 1. V.S. Shpinel. Izvestiya RAN, ser. Fiz. 64 (2000) 2216. 2. N.E. Booth, P.A. Fisher, M. Nahum, J.N. Ullom. Nuclear Instr. Meth. Phys. Res. A 444 (2000) 33.

D05. Dark Currents of Prototype Submillimeter-Wave Photon Counting Detectors

T.R. Stevenson^a, M. Li^a, R.J. Schoelkopf^b, C.M. Stahle^a, and J. Teufel^b
aNASA Goddard Space Flight Center, Code 553, Greenbelt, MD 20771 USA
^bDepartment of Applied Physics, Yale University, PO Box 208284, New Haven, CT 06520-8284 USA

A combination of single electron and superconducting tunnel junction devices with antenna coupling has been proposed as a fast submillimeter-wave detector with photon counting sensitivity. We have fabricated series of detector elements with a range of design parameters. We describe the corresponding measured dependence of dark currents on temperature and bias voltage.

D06. Multiplexing of Radio-Frequency Single Electron Transistors

T.R. Stevenson^a, K. Aidala^c, F. Pellerano^b, R.J. Schoelkopf^c, and C.M. Stahle^a
aNASA Goddard Space Flight Center, Code 553, Greenbelt, MD 20771 USA
^bNASA Goddard Space Flight Center, Code 555, Greenbelt, MD 20771 USA
^cDepartment of Applied Physics, Yale University, PO Box 208284, New Haven, CT 06520-8284 USA

We describe application of wavelength division multiplexing to combine the outputs of Radio-Frequency Single-Electron Transistors (RF-SETs). Using multiple rf carrier frequencies permits simultaneous readout of many amplifiers with a common electrical connection. Multiplexed RF-SET amplifiers could provide fast and sensitive on-chip readout of arrays of high impedance cryogenic photodetectors.

E01. SQUID-based readout schemes for microcalorimeter arrays

M. Kiviranta VTT Automation / Measurement Technology Espoo FINLAND

Microcalorimeter arrays with superconducting phase-transition thermometers are an attractive alternative for construction of imaging X-ray spectrometers. The low source impedance and low operating temperatures make a dc SQUID a good candidate for preamplifier. In large arrays, the circuit complexity as well as heat leakage through wiring make some sort of a multiplexing scheme desirable. Some circuit topologies for time-domain and frequency-domain multiplexing as well as correlation-based schemes are compared. One particular frequency-domain multiplexing circuit, being developed by VTT/Finland and SRON/Netherlands for the XEUS space mission, is reviewed in more detail. The design issues related with scalability, dynamic range, bandwidth and noise folding are discussed.

E02. SQUID Multiplexers for Large Format Arrays of Transition-Edge Sensors

K.D. Irwin^a, L.R. Vale^a, S.W. Nam^a, G.C. Hilton^a, M.E. Huber^b
aNational Institute of Standards and Technology, Boulder CO
^bUniversity of Colorado, Denver, CO

SQUID multiplexers make it possible to build arrays of thousands of low-temperature bolometers and microcalorimeters based on superconducting transition-edge sensors (TES) with a manageable number of readout channels. We discuss the constraints on the performance of the SQUID multiplexer for both x-ray and infrared applications. Our first-generation, 8-channel SQUID multiplexer (MUX) is now being deployed in one-dimensional TES arrays for submillimeter astronomy. We present our second-generation SQUID multiplexer, based on a new architecture which significantly reduces the power dissipation at the first stage, allowing thousands of SQUIDs to be operated at the base temperature of the cryostat. This performance allows the integration of the multiplexer into the focal plane, which is necessary for truly large-format bolometer arrays of many thousands of pixels. This SQUID MUX design will be used in the SCUBA-2 instrument at the James Clerk Maxwell Telescope (JCMT), which will have more than 10,000 TES submillimeter bolometer pixels. It is also a leading candidate for the multiplexer for the Constellation-X x-ray microcalorimeter instrument.

E03. Single SQUID multiplexer for arrays of voltage-biased superconducting bolometers

Jongsoo Yoon, John Clarke, Adrian T. Lee, M. J. Myers, P. L. Richards, H. G. Spieler^a
University of California, Berkeley, CA
^aLawrence Berkeley National Laboratory, Berkeley, CA

We have demonstrated a frequency-domain superconducting quantum interference device (SQUID) multiplexer for a row of low-temperature sensors [1]. Each sensor is biased with an alternating current (AC) at a distinct frequency significantly above the roll-off freqnency of the sensor and all the signals are inductively coupled to a superconducting summing loop. A single readout SQUID measures the current in the summing loop via a conventional coupling coil. The feedback from the SQUID output is used to null the total current in the summing loop, eliminating direct crosstalk between channels. We have also shown that, for a voltage-biased superconducting bolometer (VSB), the load curves taken with AC- and DC-bias are nearly identical indicating that there is no degradation in the performance of the bolometer [2]. We are currently working on the design and fabrication of a SQUID multiplexer for VSB's with tuned circuits for noise aspect. [1] J. Yoon et al., Applied Physics Letters, Vol. 78, 371 (2001). [2] J. Yoon et al., IEEE Transactions on Applied Superconductivity, submitted for publication.

E04. High frequency low noise amplifier based on the unshunted SQUID for micro-calorimeter readout

H. Seppa, M. Kiviranta, J. Hassel.
VTT Automation, Measurement Technology, Otakaari 7B, 02150 Espoo 15, Finland

We are developing a high frequency amplifier based on a SQUID circuit where damping of the flux phase for the signal frequencies is provided by the resistive source, e.g., a superconducting transition edge detector, and damping of the voltage phase by a resistive load provided by a preamplifier. This idea is based on the unshunted SQUID which was originally developed for low noise magnetometers. Owing to the reduction of the damping the noise of the SQUID can be markedly reduced. The noise at high temperatures (above 1 K) is limited by the mixed down noise between the Josephson oscillations and high frequency Johnson noise but at low temperatures (below 1 K) the noise will be limited by the quantum fluctuations at Josephson frequencies. In practice, the output noise is dominated by the noise from the resistive source and the contribution of the SQUID remains negligibly small. We will show that an unshunted SQUID and a direct feedback circuit, in addition to an integrated output transformers leads to a low noise amplifiers having extremely high dynamic range. As an example we will show how these devices can be used to detect a micro-calorimeter array using a frequency multiplexing scheme.

E05. Multiplexed Kinetic Inductance Detectors

J. Zmuidzinas^a, H. G. Leduc^b, B. A. Mazin^a, P. K. Day^b,
^aCalifornia Institute of Technology, Pasadena, CA
^bJet Propulsion Laboratory, Pasadena, CA

We are investigating a novel multiplexed readout method that can be applied to a large class of superconducting pair-breaking detectors. The readout is completely different from those currently used with STJ and TES detectors, and could deliver large pixel counts, high sensitivity, and Fano-limited spectral resolution. The readout is based on the fact that the kinetic surface inductance Ls of a superconductor is a function of the density of quasiparticles n at temperatures far below Tc. An efficient way to measure the kinetic inductance is to monitor the transmission phase of a resonant lumped-element LC circuit. By working at microwave frequencies and using thin films, the kinetic inductance can be a significant part of the total inductance L, and the volume of the inductor can be on the of order 1 cubic micron. Trapping can be used to concentrate the quasiparticles into the small volume of the inductor. However, the most intriguing aspect of the concept is that passive frequency multiplexing could be used to read out 100-1000 detectors with a single HEMT amplifier. We will present the basic detector physics, sample detector layouts, and calculations of the expected response and sensitivity. In addition, we are now working on measurements of the microwave properties of thin-film superconducting circuits, and will present our initial experimental results.

E06. AC Calorimeter Bridge; a new multi-pixel readout method for TES calorimeter arrays

Toshiyuki Miyazaki, Masahiro Yamazaki, Kazuo Futamoto, Kazuhisa Mitsuda, Ryuichi Fujimoto, Naoko Iyomoto, Tai Oshima, Damian Audley, ^a, Yoshitaka Ishisaki, Noriko Yamasaki, Takaya Ohashi, Tomohiro Kagei^b, Shuichi Shoji, Hiroyuki Kudo, Yuichi Yokoyama^c,
^aISAS
^bTokyo Metropolitan University
^cWaseda University

In order to realize a large format (e.g. ~ 32 × 32 ) calorimeter array, it is essential to multiplex calorimeter signals at cryogenic temperatures without losing signal to noise ratio. For this purpose we propose a brand-new readout method, the CABBAGE (CAlorimeter Bridge Biased by an AC Generator) where an AC biased calorimeters are placed in resistance bridges. In this paper we first describe the principles of CABBAGE and investigate its response and noise. We find that the degradation of energy resolution can be made negligibly small by appropriate choice of bridge resistances. We applied this method to a 2 × 1 pixel Ti-Au TES calorimeter array. We biased the two calorimeter pixels at 10 and 20 kHz, respectively. The bridge resistances were adjusted to suppress the output current to zero when there is no X-ray signal. The signals from the two calorimeter bridges were added together at the 2 K stage by a special DC SQUID which contains four independent input coils. We obtained X-ray signals from both pixels and successfully identified the pixels in which the signals were generated . This demonstrates that the present method is promising for future applications in imaging X-ray calorimeters.

E07. Characteristics of transition-edge microcalorimeters under AC bias

J. van der Kuur^a, W.A. Mels^a, M.A.N. Korevaar^a, P.A.J. de Korte^a
M. Kiviranta^b, Heikki Seppa^b
aSpace Research Organization Netherlands, Sorbonnelaan 2, 3584 CA Utrecht, the Netherlands
^bVTT Automation/Measurement Technology, PO Box 1304, FIN-02044 VTT, Finland

Microcalorimeters based on transition-edge sensors (TES) nowadays achieve energy resolutions which are compatible with future astronomical applications. One of the next steps towards application of this type of sensors is development of readout concepts for imaging arrays. Frequency multiplexing is one of the possible concepts currently being studied. AC biasing of the sensors is an elegant way of implementing this way of multiplexing. This paper will address consequences of AC biasing on the performance of transition-edge microcalorimeters. Amongst the presented effects are noise modulation and demodulation and frequency distribution of the well known noise sources. Secondly, the current dependence of the transition of a TES introduces nonlinear behaviour under AC bias. The implications of this behaviour on the signal and noise of the sensor will be analyzed. Finally, consequences of the described behaviour on the design of a sensor array will be discussed.

E08. AC biasing of a Transition Edge Sensor Microcalorimeter

M. F. Cunningham1,2,3, J. N. Ullom2, T. Miyazaki2, O. Drury2, A. Loshak2, M. L. van den Berg2, M. Frank2, S. E. Labov2 2 Physics and Advanced Technologies Directorate, Lawrence Livermore National Laboratory 3 Department of Applied Science, University of California at Davis

We are developing arrays of microcalorimeters based on superconducting transition edge sensors (TESs). We have developed a full-wafer process for fabricating the detector arrays. Each detector consists of a Mo/Cu multilayer TES on a thin SiN membrane with Mo wiring leads. The multilayer construction of the TES allows us to use a wide variety of thicknesses, and therefore resistivities, without changing the superconducting properties. To read out our arrays, we are exploring a multiplexing scheme that works in the frequency domain. In this scheme, multiple detectors can be measured with a single SQUID amplifier because each pixel is AC biased at a distinct, identifying frequency. By using bias frequencies significantly above the thermal response frequency of the detectors, we should be able to achieve stable operation and undegraded energy resolution. We will present measurements of the energy resolution of single microcalorimeters subject to DC and AC biases. This work was performed under the auspices of the U. S.Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract No. W-7405-ENG-48.

E09. TES Detector Noise Limited Readout Using SQUID Multiplexers

J. Staguhn^a, C. Allen^a, D. Benford^a, J. Chervenak^a, M. Freund^a, S. Khan^a, A. Kutyrev^a, S.H. Moseley^a, R. Shafer^a, S. Deiker^b, E. Grossman^b, G. Hilton^b, K. Irwin^b, J. Martinis^b, S.W. Nam^b, D. Rudman^b, D. Wollman^b
a NASA/Goddard Space Flight Center
^b NIST-Boulder

The availability of superconducting Transition Edge Sensors (TES) with large numbers of individual detector pixels requires multiplexers for efficient readout. The usage of multiplexers limits the number of wires needed between the cryogenic electronics and the room temperature electronics and limits the number of required cryogenic amplifiers. We are using an 8 channel SQUID multiplexer to read out one dimensional TES arrays which are used for submillimeter astronomical observations . We present results from test measurements which show that the low noise level of the SQUID multiplexers allows accurate measurements of the TES Johnson noise, and that in operation, the SQUID noise is dominated by the detector noise. Multiplexers for large number of channels require a large bandwidth for the multiplexed readout signal. We discuss the resulting implications for the noise performance of these multiplexers which will be used for the readout of two dimensional TES arrays in next generation instruments.

E10. A new readout scheme for imaging TES based on cooling time measurement

Y. Noguchi*a, H. Takahashi*b, D. Fukuda*a, M. Ohno*a, M. Nakazawa*a, M. Ataka*c, M. Ukibe*d, F. Hirayama*d, M. Ohkubo*d *a Department of Quantum Eng. and Systems Sci., The University of Tokyo, Tokyo *b RACE, The University of Tokyo, Tokyo *c Institute of Industrial Science, The University of Tokyo, Tokyo *d National Institute of Advanced Industrial Science and Technology, Ibaraki

We are developing a tungsten transition edge sensor (W-TES) for x-ray imaging spectroscopy applications. The conventional readout method for TES array has a great difficulty in reading out multi-channel x-ray signals. Therefore we have considered a new readout scheme for a W-TES array. Now we consider W-TES pixels that have small heat capacity (about 10-13J/K) and very sharp transition. They can quite easily turn to the normal conducting state by absorbing the energy of one incident x-ray photon, therefore saturated signals are observed. If we assume the constant heat flow from the TES to the heat bath, the cooling time of the W-TES is proportional to incident x-ray energy and then we can obtain an x-ray energy spectrum by measuring the cooling time. In this "digital TES" operation mode, we only need time information, therefore we can expect to simplify the electronics. Moreover the thermal time constant of the W-TES must be shorten to measure the cooling time with high accuracy, it means that the W-TES can be operated at high-count rate. Although the currently achieved energy resolution of our W-TES (0.5mmx0.5mm) using the cooling time measurement is 62eV (FWHM) at 5.9keV, much higher energy resolution is expected for smaller devices.

E11. A 15 microK Noise Temperature SQUID Amplifier For Ultracryogenic Gravitational Wave Detectors

P. Falferi(a), M. Bonaldi(a), M. Cerdonio(b), A. Vinante(c), R. Mezzena(c), G. A. Prodi(c), S. Vitale(c) (a) Centro di Fisica degli Stati Aggregati and INFN, Gruppo Collegato di Trento, Sezione di Padova, I-38050 Povo, Trento, Italy (b) Dipartimento di Fisica, Universit� di Padova and INFN, Sezione di Padova, via Marzolo 8, I-35131, Padova, Italy (c) Dipartimento di Fisica, Universit� di Trento and INFN, Gruppo Collegato di Trento, Sezione di Padova, I-38050 Povo, Trento, Italy

A two-stage SQUID amplifier based on a commercial sensor is operated strongly coupled to an electrical resonator which simulates, as regards resonance frequency (1 kHz) and quality factor (10⁶), the load of one of the mechanical modes of a cryogenic gravitational wave detector. The behaviour of the system is stable and, in the temperature range 1.5-4.2 K, the noise of the resonator is in agreement with the equipartition theorem. Thanks to the very high quality factor it is possible to evaluate the back action noise of the SQUID amplifier which is found to be thermal and in agreement with the theory. The open input broadband noise is also thermal and in agreement with the theory down to 300 mK and levels off to a constant value which corresponds to 35 hbar at lower temperatures. The noise temperature of the SQUID amplifier, obtained from the broadband and back action noise measurements, is 15 microK at 1.5 K. On the basis of these results the operation of a resonant gravitational wave detector with an amplifier with an energy sensitivity better than 100 hbar seems achievable.

E12. The 66-channel SQUID readout system for CRESST II

H. Kraus, N. Bazin, S. Cooper, S. Henry
University of Oxford, Department of Physics, NAPL, Keble Road, Oxford OX1 3RH

The upgrade of the CRESST experiment to a 10kg target of phonon / light detectors necessitates the installation of 66 readout channels in the CRESST cryostat. We report on the status of this upgrade and discuss the issues related to the installation of the correspondingly high number of wires in an ultra-low temperature environment.

E13. Readout Electronics for Arrays of TES detectors

S. Nam, D.A. Wollman, A.J. Miller, G. Hilton, J.M. Martinis
National Institute of Standards and Technology

The performance of single pixel transition edge sensors (TES) is useful for a variety of applications including X-ray microanalysis and the detection of photons from the sub-millimeter to gamma rays, arrays of TES's are required in the next generation instruments to continue to be useful. We report on the development and performance of a readout electronics system used to readout and process signals from arrays of TES detectors. The system utilizes flex cabling, high performance analog electronics, and digital signal processing. The system simplifies and automates the setup of each pixel and reduces the cost per channel, thus enabling the instrumentation of a large numbers of channels. The use of digital processing also improves the performance of the system. As an example, for X-ray microanalysis the energy resolution increases from 4 eV FWHM at 1.5 keV with an analog system to 3 eV FWHM with the digital system. We will also describe the latest operation of the electronics with arrays of TES detectors used in X-ray microanalysis and optical astronomy.

E14. THE FRONT-END SYSTEM FOR AN ARRAYS OF micro-BOLOMETERS

C.Arnaboldi, C.Brofferio, O.Cremonesi, A.Giuliani, A.Nucciotti, M.Pavan, G.Pessina, S.Pirro, E.Previtali^a,
^aINFN Istituto Nazionale di Fisica Nucleare, e Dipartimento di Fisica dell'Universit� di Milano-Bicocca P.za Della Scienza 3, 20126 Milano, Italy
ND

We present the details used for the realization of the readout of our array of micro-bolometers for the study of the beta decay of Re. The analog acquisition chain has been realized fully programmable in the parameters of interest, for obtaining the optimum detector performance. One front-end channel is located on each card and can be controlled individually. A front-end is composed of a load resistors-bias system, a cold stage, a differential voltage preamplifier, an amplifier and a shaping filter. The load resistors can be selected between two values and the biasing given to detector can be attenuated with 5 bits of resolution, for selecting the optimum current for each bolometer individually. The amplifier has the gain that ca be changed in 5 steps and the shaping filter can change the time constant 4 steps. A small power consumption Complex Programmable Logic Device, CPLD, is the core of the digital part of the system. It controls the analog section of the board under the master computer managing. The clock of the system normally sleeps and is waked-up only when the master address the board. The output offset voltage can be adjusted, remotely, at any arbitrary level. All the front-end features will be described in detail.

E15. A FRONT-END PREAMPLIFIER FOR THE READOUT OF micro-BOLOMETERS

C.Arnaboldi, C.Brofferio, O.Cremonesi, A.Giuliani, A.Nucciotti, M.Pavan, G.Pessina, E.Previtali^a,
^aINFN Istituto Nazionale di Fisica Nucleare, e Dipartimento di Fisica dell'Universit� di Milano-Bicocca P.za Della Scienza 3, 20126 Milano, Italy
ND

We present our front-end solution for the readout of an array of micro-bolometers for the study of beta decay of Re. The front-end consists of a Si JFET cold stage followed by a second stage located at room temperature. The design of both parts has been made with the aim of obtaining low noise and to suppress EMI interference as much as possible. The second stage has differential inputs and outputs voltage signals and it is able to accept large DC voltage excursion at its inputs. A study has been made on dynamic and noise behavior of the selected Si JFET cold stage down to LHe. Results will be shown in details.

E16. THE TRIGGER SYSTEM FOR AN ARRAYS OF LARGE MASS BOLOMETERS

C.Arnaboldi, C.Bucci, C.Brofferio, O.Cremonesi, A.Giuliani, A.Nucciotti, M.Pavan, G.Pessina, E.Previtali^a,
^aINFN Istituto Nazionale di Fisica Nucleare, e Dipartimento di Fisica dell'Universit� di Milano-Bicocca P.za Della Scienza 3, 20126 Milano, Italy
ND

CUORICINO is an array of more than 50 large mass TeO2 bolometric detectors that will study the double beta decay of Te and will search for the dark mass of the universe. For the latter application very accurate triggering of small signals will be necessary to investigate possible dark matter candidates. We describe our trigger circuit realized for obtaining precise signal selection and avoiding the problem of the re-triggering of large signals tails.

E17. Modeling of an active feedback preamplifier at cryogenic temperatures

S. Saramad(1) P. Jarron(2) M. Bucher(3) (1) Amir Kabir University, Tehran, Iran (2) CERN, Geneva, Switzerland (3) National Technical University of Athens, Greece

In many applications such as the study of prompt dimuon and charm production with proton and heavy ion beam and several other CERN projects, radiation hardness of silicon detectors and some electronic devices is important and this requires high performance readout electronic at cryogenic temperatures. The transimpedance amplifier presented in this paper is a low noise, high speed preamplifier with current feedback and adjustable gain and good stability, which is fully integrated by quarter micron CMOS technology and compatible with submicron digital CMOS devices. Our experimental results show that this preamplifier can be used at cryogenic temperatures till 70 K with an improved performance in comparison to room temperature. Although the characteristic of this preamplifier is optimized for room temperature, it has also a reasonable response till 20 K without changing the bias points. In addition by extracting the parameters of MOS transistors of this preamplifier at cryogenic temperatures and modeling the behavior of this preamplifier, it was found that by optimizing some parameters and modifications, this preamplifier can also be usable till 4.2 K. The fast rise time (<6ns) and low Equivalent Noise Charge (ENC) of this preamplifier making it very promising for high-speed and low- noise applications at cryogenic temperatures.

F01. Optimal Fitting of Nonlinear Detector Responses

D. J. Fixsen^a,b, S. H. Moseley^a
aLaboratory for Astronomy and Solar Physics, NASA/GSFC
^bRaytheon ITSS

Optimal extraction of pulses of constant known shape from a time series with stationary noise is well understood and widely used in detector applications. In applications where high resolution is required over a wide range of input signals, the detectors may have significant nonlinearities: the pulse shape may vary with input signal amplitude and the noise may also vary with the signal amplitude. We present a general method for optimally fitting such nonlinear detector responses and extracting the input signals.

F02. Data Processing for Large Fast Microcalorimeter Arrays

Boyce, K.R.¹, Figueroa-Feliciano, E.¹, Finkbeiner, F.M.² Gendreau, K.C.¹, Kelley, R.L.¹, Lindeman, M.A.¹, Porter, F.S.¹, Stahle, C.K.¹, Szymkowiak, A.E.^1
1NASA/GSFC, Greenbelt, Maryland, USA
²University of Maryland, College Park, Maryland, USA

Future missions such as Constellation-X plan to use arrays of 1000 or more microcalorimeters with peak count rates of 1000 per second on a single pixel and 10,000 per second across the array. These requirements put severe constraints on the data processing system. Raw data from the array will exceed 3 Gbits/second. In addition, the limited power available on spaceflight missions requires a highly efficient processing system. We discuss a possible data processing architecture that will fit within the constraints of Constellation-X.

F03. Data Reduction Methods for a Micro-Calorimeter Sounding Rocket Flight

W. T. Sanders ^a, M. Galeazzi ^a and F. S. Porter ^b
aUniversity of Wisconsin, Madison, WI 53705 USA
^bNASA/Goddard Space Flight Center, Greenbelt, MD 20771 USA

Using a micro-calorimeter detector on a sounding rocket experiment creates difficulties in the data analysis that are not normally encountered on the ground or on satellite base experiments. In analyzing the data obtained from two recent sounding rocket flights that employed micro-calorimeter detectors, we have developed procedures for reducing the raw data to a data set suitable for astrophysical analysis. The data acquired from the instrument include fully sampled digitized waveforms for each X-ray event plus "quick-look" X-ray pulse heights from an on-board analog pulse shaping circuit, and large quantities of housekeeping information. In the post-flight data analysis we first characterize the events, then the X-ray waveforms from each pixel are digitally filtered, gain-drift corrected, and an energy scale is applied before combing the events into a single spectrum. Our final product is a set of events that were with high probability produced by the X-ray photons that we attempted to measure and that are well-characterized and free from systematic biases. In this poster, we discuss our procedures and algorithms and the difficulties that we encountered in the data reduction.

G01. Cryogenic Detector Systems for Materials Analysis

J. Hohne ^a
aCSP Cryogenic Spectrometers GmbH, Bahnhofstr. 18a, D-85737 Ismaning, Germany

The need to analyze small amounts of materials on surfaces e.g. in semiconductor industry drives the development of high resolution X-ray spectrometers based on superconducting detector technology. Since low excitation energies in Field Emission Electron Microscopes (FESEM) only yield X-ray lines in the lower part of the X-ray spectrum (<5keV), line overlaps become a serious issue in the spectral analysis. This problem can be overcome with superconducting detector technology having better energy resolution and thus the ability to separate X-ray lines of important material combinations. For industrial applications the cooling system for the superconducting sensor plays an important role, since liquid coolants are not being tolerated in clean room environments. This talk will cover the basic needs of the materials analyst as well as the practical implementation of superconducting X-ray spectrometers for industrial applications.

G02. A multichannel cryogenic detector system for synchrotron-based x-ray spectroscopy

S. Friedrich^a,b, T. Niedermayr^a, T. Funk^b, O. Drury^a, M. L. van den Berg^a, M. F. Cunningham^a J. N. Ullom^a A. Loshak^a, S. P. Cramer^b, M. Frank^a, S. E. Labov^a,
^aLawrence Livermore National Laboratory, L-418, Livermore, CA 94551
^bLawrence Berkeley National Laboratory, MS 6-2100, Berkeley, CA 94720

Fluorescence-detected x-ray absorption spectroscopy probes the fine structure of electronic bands with sub-eV resolution by scanning a monochromatic synchrotron beam through the corresponding absorption edge and measuring the intensity of the resulting x-ray fluorescence. For dilute samples, grating spectrometers lack the detection efficiency and conventional Si(Li) or Ge detectors often lack the energy resolution to separate the weak fluorescence signal from strong nearby emission lines. We have built a high-resolution high-efficiency cryogenic detector system for synchrotron-based x-ray spectroscopy. The sensor is a 3 × 3 array of 200µm × 200µm superconducting Nb-Al-AlOx-Al-Nb tunnel junctions with an energy resolution around 10-15 eV below 1 keV and a total count rate capability of ~100,000 counts/second. This sensor array is cooled to ~0.1K by a two-stage adiabatic demagnetization refrigerator while held at the end of a 40-cm-long snout that can be inserted into a UHV chamber for x-ray fluorescence measurements. We will present absorption spectra of dilute compounds (~1000 ppm) and will discuss spectrometer performance with respect to the analysis of metalloproteins. This work was performed under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.

G03. INVESTIGATION OF SUPERCONDUCTING TUNNEL JUNCTION DETECTORS FOR LOW-ENERGY X-RAY FLUORESCENCE ANALYSIS USING MONOCHROMATISED UNDULATOR RADIATION

B. Beckhoff, R. Fliegauf and G. Ulm
Physikalisch-Technische Bundesanstalt, Abbestraße 2-12, D-10587 Berlin, Germany

Modern applications of energy-dispersive x-ray fluorescence analysis (EDXRF) in the soft x-ray range, such as material and surface analysis, require an improved energy resolution. Here, the energy resolution of conventional semiconductor detectors is often not sufficient to discriminate simultaneously K-shell fluorescence lines of light elements from L-shell fluorescence lines of transition metals. Superconducting tunnel junction (STJ) may contribute to overcoming this restriction in low-energy EDXRF. The Physikalisch-Technische Bundesanstalt (PTB) operates a cryogenic STJ detector system, provided by Lawrence Livermore National Laboratory. The STJ is operated at temperatures below 400 mK at the end of a 23 cm long cold finger inside a liquid He and a liquid N2 cooled shield, allowing for effective fluorescence detection in a ultra-high vacuum environment. The PTB plane grating monochromator beamline for undulator radiation at the electron storage ring BESSY II provides monochromatic radiation of high spectral purity which was employed both for STJ characterisation and specimen excitation. Here, both the energy resolution and the absolute detection efficiency of STJ detectors were investigated below 2 keV to define restrictions of STJ applications in EDXRF. In simultaneous EDXRF experiments ensuring identical observation conditions, the performance of the STJ detector is compared to a Si(Li) detector calibrated absolutely. Perspectives for trace analysis on wafer surfaces will be given.

G04. X-ray spectroscopy of ion/surface interaction using superconducting tunnel junctions

T. Niedermayr^1,2, S. Friedrich¹, Mark Cunningham¹, Matthias Frank¹, Jean-Pierre Briand², Simon Labov^{1 1}Lawrence Livermore National Laboratory, L-418, Livermore, CA 94551, USA ²Pierre and Marie Curie University, 75005 Paris, France

The interaction of highly charged ions with surfaces has drawn considerable attention in the last few years driven by the possibility to modify surfaces on a sub-micron scale. Most studies to date have been done using Auger spectroscopy, but electrons are very sensitive to the large electric fields present at the surface. X-rays on the other hand are insensitive to these fields and permit the study of the interaction at and below the surface. We have conducted for the first time in the field of ion/surface interaction low energy X-ray spectroscopy with a cryogenic detector. The Nb-Al-AlOx-Al-Nb junctions are operated in an adiabatic demagnetization refrigerator with 60 mK base temperature at the end of a 40-cm-long cold finger, which can be inserted into a UHV chamber. We studied the interaction of fast light ions with various targets. The resolution of 12-15 eV below 1 keV enabled us to separate for the first time the different satellite lines emitted by these ions. We will present these results and discuss new insights gained on the interaction of highly charged ions with surfaces. This work was performed under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.

G05. Comparison between BEFS and EXAFS analysis for microcrystalline study of rhenium metal.

F. Gatti, D. Pergolesi, M. Razeti - University and INFN of Genoa - F. D'Acapito, S. Mobilio - ESRF Grenoble - F. Gonella, C. Maurizio - University of Padova -

BEFS can be used for the study of microcrystalline structure by means of microcalorimetric detectors. To evaluate the precision and the reliability of this new method we performed a comparison with EXAFS analysis. For this purpose the K-edge EXAFS measurements on rhenium metal have been done at the European Synchrotron Facility. The preliminary results indicate that BEFS analysis allow to measure the interatomic distances with resolution of hundredths of Angstrom as good as in the EXAFS.

H01. Space Cryogenics for Low-Temperature Applications

Rob Boyle NASA Goddard Space Flight Center, Greenbelt, MD

What the agency refers to as "Space Science" represents the broadest application of cryogenic technology within NASA. Ongoing use of superfluid helium systems will be described, as well as new work on closed-cycle cooling systems in the 4-10K and sub-Kelvin ranges.

H02. Integrated SINIS coolers for efficient cooling of cryogenic detectors

A. Luukanen,A.M. Savin, T.I. Suppula, and J.P. Pekola
University of Jyv�skyl�, Department of Physics, Jyv�skyl�, Finland

A. Luukanen, A.M. Savin, T.I. Suppula, and J.P. Pekola Our goal is to demonstrate the feasibility of a single pixel or small arrays of microcalorimeters or microbolometers, coupled to on-chip coolers. The benefit of such a configuration is that the system bath temperature can be much higher than the detector temperature without degraded detector noise performance. We have previously demonstrated SINIS coolers capable of electron cooling starting from 0.3 K to 0.1 K. Cooling power of one junction pair is several tens of picowatts which is due to relatively large junction size (~ 300 µm²), and efficient trapping of hot quasiparticles to an underlying trap layer. The current work focuses on the technological challenges of integrating the cooler with microcalorimeters, as packing density and system complexity are critical issues in large arrays of microcalorimeters. We also discuss promising new results obtained with superconductor-semiconductor-superconductor (S-Sm-S) tunnel junctions, in which the Schottky barrier of the semiconductor is used as the tunnel barrier. This technique opens up new possibilities, since the delicate growth of thin AlOx tunnel barrier can be omitted. References A.M. Savin et al. �Efficient electronic cooling in heavily doped semiconductor by quasiparticle tunnelling�, preprint (2001)

H03. A solid-state microrefrigerator based on NIS tunnel junctions with a superconducting single crystal substrate

M.L. van den Berg^a, J.N. Ullom, S.E. Labov
^aLawrence Livermore National Laboratory, Livermore, CA

We are developing a solid-state microrefrigerator based on Normal-Insulator-Superconductor (NIS) tunnel junctions. NIS tunnel junctions are a promising means of providing continuous refrigeration from 0.3 to 0.1 K. Previously, the area and cooling power of NIS refrigerators have been limited by heating of the superconducting electrode. This problem can be overcome by using a superconducting single crystal as both the substrate and superconducting electrode of the NIS junction. The long quasiparticle mean-free-path and large volume of the crystal prevent the accumulation of quasiparticles near the junction which degrades the performance of thin-film devices. For undegraded performance, the single crystal substrate must be exceptionally smooth. By exploring various polishing techniques we have achieved Al single crystal surfaces with an RMS roughness less than 1 nm. Previous work on superconducting tunnel junctions based on superconducting single crystals for X-ray detectors has shown that this surface smoothness is adequate. We are currently integrating our NIS tunnel junction fabrication process with Al single crystal substrates. We expect to show our first measurements of NIS refrigerators with a superconducting single crystal substrate. This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract No. W-7405-ENG-48.

H04. A Continuous Low-Temperature Magnetic Refrigerator

P. J. Shirron^a, E. R. Canavan^a, M. J. DiPirro^a, M. L. Jackson^a, T. T. King^b, J. S. Panek^a, J. G. Tuttle^a,
^aCode 552, NASA/GSFC, Greenbelt, MD
^bCode 541, NASA/GSFC, Greenbelt, MD

We report on recent progress in the development of a continuous adiabatic demagnetization refrigerator (ADR). This system uses multiple stages to cyclically transfer heat from a load up to a heat sink. Continuous operation avoids the constraints of long hold times and short recycle times that lead to the generally large mass of single-shot ADRs, allowing us to achieve an order of magnitude larger cooling power per unit mass. Our current design goal is 10 �W of cooling at 50 mK using a 6-10 K heat sink. The estimated mass is less than 10 kg, including magnetic shielding of each stage. These parameters envelop the cooling requirements for all currently planned space astronomy missions. The relatively high heat rejection capability allows it to operate with a mechanical cryocooler as part of a cryogen-free, low temperature cooling system. This has the advantages of long mission life and reduced complexity and cost. This paper will discuss details of the design and operation of the ADR, interface requirements for cryocooler-based operation, and anticipated performance of the complete system.

H05. Entropy behavior of Er-doped YAG for the application of ADR

A. Kushino, Y. Aoki, N. Y. Yamasaki, Y. Ishisaki, T. Ohashi^a, K. Mitsuda^b
aTokyo Metropolitan University
^b The Institute of Space and Astronautical Science

Garnet doped with rare-earth element is proposed for ADR (adiabatic demagnetization refrigerators). We have measured specific heat and magnetization of a single crystal YAG (yttrium aluminum garnet) doped with 30% Er³⁺ ion at temperatures between 93 mK and 8 K under magnetic fields u p to 8.0 T along the langle 111 rangle crystal axis. From specific heat and magnetization, we consistently derived the temperature and magnetic-field dependences of magnetic entropy. Under zero magnetic field, it starts to decrease below 2 K and becomes half of Rln2 at ~ 160 mK. This decrease is considered to be due to an antiferromagnetic short-range ordering among Er³⁺ ions. The behavior of specific heat in the measured temperature range can be explained by a model in which both the crystalline-electric-field ground state and the first excited state are included. As a magnetic coolant, the operating temperature with the erbium-doped YAG is estimated down to ~ 100 mK, which is lower than those with non-substituted garnets such as GGG (garium gadrinium garnet) used in the range ~ 4.2 - 15 K\@. With the doping level of 30%, we estimate that ~ 6 kg of erbium-doped YAG exhibits the same cooling performance at 60 mK as the 916 g of salt pill employed in the Astro-E satellite for micro-calorimeters.

H06. A Miniature Adiabatic Demagnetization Refrigerator

M. P. Supanich^a, P. T. Timbie^a
aUniversity of Wisconsin, Madison, WI

Adiabatic Demagnetization Refrigerators (ADRs) have been used for many years to cool bolometers, microcalorimeters, and other types of detectors. Recent and future space research projects have used or could use detectors cooled to very low temperatures to optimize observations. Unfortunately, ADRs have traditionally been bulky, expensive, difficult to construct, and unreliable. We present the design of a novel, miniature ADR with no moving parts, which could be used for astrophysics research, semiconductor analysis, and mass spectrometry. The miniature ADR relies on the development of a magnetoresistive heat switch, which will be discussed.

H07. Excess Noise in Cryogenic Detectors due to Vibrating 1 K Pots

A. Raccanelli^a, L. A. Reichertz^a, E. Kreysa^a,
^aMax Planck Institut fuer Radioastronomie, Bonn, Germany

Temperatures between 4 K and 1 K are obtained by pumping on a ⁴He bath. In order to reduce the consumption of liquid helium, it is common to pump only on a small volume of He inside a small chamber (1 K pot), continuously replenished from a main bath at 4.2 K, through an impedance. 1 K pots are a necessary cooling step in dilution refrigerators, used to cool many different kind of sensitive detectors to temperatures in the mK range, e.g. gravitational antennas, bolometers for far-infrared radiation or high resolution particle detection. It is known that continuously filled 1 K pots are affected by vibrations that are a source of excess noise, and thus can decrease the performance of the detectors. We present our study on the origin of these vibrations and a solution we have found to eliminate this excess noise from the detectors.

H08. Cryogenic sources for low temperature detectors characterisation

E. Leblanc* , V. Tsoupko-Sitnikov, J. F. Metge, N. Coron, J. Leblanc
CEA \ DIMRI \ Laboratoire National Henri Becquerel

Low temperature detectors studies require non-contaminating cryogenic sources covering a wide range of energies and activities. For detector calibration in case of low background measurements, it is of prime interest to have very low activity sources of well-known emission flux. We have developed non-contaminating small sources on very pure gold supports (diameter les than 1 mm). Any convenient nuclide can be deposited. Low activity level is traceable. We have also made encapsulated sources that can be driven close to the detector then removed by a pneumatic system. Microcalorimeters and tunnel junctions often present small detection solid angle. In order to study energy resolution or detection efficiency, high activitiy sources are necessary. We have prepared 1 GBq 55Fe source by electrodeposition. The source has been characterised by a dispersion X-ray spectrometer. Multiple-energies sources are sought-after for determination of linearity and voltage energy response of detectors. Therefore we have designed a radioactive source with an integrated optical-fibre linked to an IR LED. Using a pulse generator, we can irradiate our microcalorimeter with packets of photons of calibrated energy over an energy range from few tens of eV up to several keV.

H09. Fabrication of IR blocking filter for low energy X-ray applications

K. L. Nelms, M. Galeazzi, D. Liu, D. McCammon, N. Moeckel, W. T. Sanders, and P. Tan
University of Wisconsin, Madison, WI 53706 USA

Sufficient IR filtration and high X-ray throughput are essential elements of experiments using low temperature x-ray detectors for space applications. On our current sounding rocket payload, for example, we use five 180-A aluminum filters in series, each supported on a 1000-A parylene film, to shield the cold stage of the refrigerator. There are several problems regarding the stated method. First, the parylene film is not of uniform thickness. In addition, the x-ray transmission of the parylene is too low, particularly at energies less than 200 eV. Also, the outer IR filter is subject to collecting ice crystals during the cooling down procedure, due to the residual water in the refrigerator. Previously, we have attached a wire heater to the filter's ring support and applied current to evaporate the ice. However, this is an impractical method. We are studying a new filter fabrication approach exercising basic microelectronic techniques. Liquid polyimide is available with the potential to be spun on a silicon wafer resulting consistently in a thickness of 200 A. The silicon wafer can then be fabricated into a fine mesh support grid for maximum X-ray transmission and, via ion implantation, a heater could be patterned into it. Such structure should be able to addresses the above problems and be suitable for space application.

J01. Calorimetric low temperature detectors for mass identification of heavy ions

S. Kraft^a,b, A. Bleile^a,b, P. Egelhof^a,b, R. Golser^c, O. Kisselev^a, W. Kutschera^c, V. Liechtenstein^c, H. J. Meier^a, A. Priller^c, A. Shrivastava^a,b, P. Steier^c, C. Vockenhuber^c, M. Weber^a,b
aGesellschaft für Schwerionenforschung, Darmstadt, Germany
^bInstitut für Physik, Johannes-Gutenberg-Universitaet, Mainz, Germany
^cVERA Laboratory, Institut für Isotopenforschung und Kernphysik, Universitaet Wien, Vienna, Austria

Calorimetric low temperature detectors (LTDs) have already been demonstrated [1] to provide an excellent relative energy resolution of 1--2×10^-3 for energetic heavy ions in a wide range of ion species and energies (E=5--1000MeV/amu). Such investigations have recently been extended to the energy range of E=0.1--1MeV/amu, commonly used for accelerator mass spectrometry (AMS). Here, calorimetric LTDs are expected to provide considerable advantage over conventional detectors with respect to detection efficiency and energy resolution. Systematic studies were performed using various beams provided by the Vienna 3MV Tandem accelerator. The detectors consist of sapphire absorbers and superconducting aluminium strip thermometers, operated at T~1.5K. For 30MeV ²³⁸U an excellent energy resolution of 150keV has been obtained. With the achieved performance, the present LTDs bear a large potential for applications in various fields of heavy ion research. Of special interest is isotope mass identification via combined high resolution energy and time of flight (TOF) measurement. Results of recent test measurements performed with the present LTDs and a conventional TOF spectrometer are encouraging. Such a detection scheme may provide in future substantial background suppression for AMS measurements. Furthermore, it may be of considerable value for identification of superheavy elements with Z>114. [1] P. Egelhof, Advances in Solid State Physics {bf 39} (1999) 61

J02. Calorimetric Low-Temperature Detectors for High Resolution X-Ray Spectroscopy on Stored Highly Stripped Heavy Ions

A. Bleile^a,P. Egelhof^a, S. Kraft^a, D. McCammon^b, H. J. Meier^a, A. Shrivastava^a, C. K. Stahle^c, M. Weber^a
aInstitut für Physik,Johannes-Gutenberg-Universitaet Mainz and Gesellschaft für Schwerionenforschung Darmstadt, Germany ^bDepartment of Physics, University of Wisconsin, Madison, USA ^cNASA/Goddard Space Flight Centre, Greenbelt, USA

The precise determination of the Lamb shift in heavy hydrogen-like ions provides a sensitive test of quantum electrodynamics in very strong Coulomb fields, not accessible otherwise. For the investigation of the 1s Lamb shift in ²⁰⁸Pb⁸¹⁺ or ²³⁸U⁹¹⁺ at the heavy ion storage ring ESR of GSI Darmstadt a high resolving x-ray detector for hard x-rays (E <= 100 keV) is needed to measure the Lyman-alpha transitions with sufficient accuracy. For this purpose, a calorimetric low-temperature x-ray detector is presently developed. The detector modules consist of silicon thermistors and x-ray absorbers glued on top of them. Thermistor arrays, consisting of 36 pixels each, are provided from the collaborating groups from Madison and Goddard. For the Lamb shift measurement the experimental setup was optimized with respect to energy resolution and detection efficiency for hard x-rays. Systematical tests of various absorber materials and geometries were recently performed using 60 keV photons, provided by an ²⁴¹Am source. The detector performance presently achieved is already close to fulfill the demands of the Lamb shift experiment. The best results were obtained with Pb as absorber material. For a detector with a 0.2mm²×47µm absorber an energy resolution of DeltaE_FWHM =65eV is achieved.

J03. Recent results From the Low Temperature Spare Astro-E Microcalorimeter Used at the LLNL ebit-ii.

G. V. Brown ^a, E. Behar ^c, P. Beiersdorfer^b, K. R. Boyce^a, H. Chen^b, K. C. Gendreau^a, J. Gygax^a, S. M. Kahn^c, R. L. Kelley^a, F. S. Porter^a, C. K. Stahle^a, A. E. Szymkowiak^a,
^aNASA/GSFC, Greenbelt, Maryland, USA
^bLawrence Livermore National Laboratory, Livermore, CA, USA
^cColumbia Astrophysics Laboratory, Columbia University, New York, NY, USA

In the past year a spare NASA/GSFC Astro-E microcalorimeter has been installed, tested, and run successfully on ebit-ii at the Lawrence Livermore National Laboratory. The microcalorimeter complements crystal and grating spectrometers already present at ebit-ii making it possible to measure a broad bandwidth (~ 0.3--10 keV) with moderate resolution while simultaneously measuring a narrow bandwidth (~ 0.7--1.3 keV) with high resolution. Recent results including measurements by the microcalorimeter of absolute excitation cross sections, time dependent spectra, and spectra as a function of Maxwellian temperature will be presented. These results continue our effort to provide atomic data of high quality to be used as benchmarks of theoretical calculations and to be included in atomic data bases employed by spectral fitting packages used to interpret spectra obtained by XMM-Newton and the Chandra X-Ray Observatory. Work by the UC-LLNL was performed under the auspices of DOE under contract W-7405-ENG-48 and supported by NASA Space Astrophysics Research and Analysis grants to LLNL, GSFC, and Columbia University.

J04. X-ray Spectroscopy of Exotic Ions With an X-ray Microcalorimeter

S.R. Bandler^a, E.H. Silver^a, H.W. Schnopper^a, S.S. Murray^a, N. Madden^b, D. Landis^b, J. Beeman^b, E.E. Haller^b, J.D. Gillaspy^c, E. Takacs^c, I. Kink^c, M. Barbera^d, M. Artale^d
aSmithsonian Astrophysical Observatory, Cambridge, MA
^bLawrence Berkeley National Laboratory, Berkeley, CA ^cNational Institute of Standards and Technology, Gaithersburg, MD ^dOsservatoria Astronomico di Palermo, Palermo, Italy

We are engaged in broad band, high resolution microcalorimeter measurements of astrophysically relevant ionic species to obtain emission line ratios and excitation cross-sections. We are also investigating the properties of exotic hollow atoms, in particular, the neutralization and relaxation that occurs at solid surfaces, with emphasis on measuring x-ray spectra from several steps in the recombination cascade. We have built a cryogenic spectrometer system that was specifically designed for the NIST EBIT (Electron Beam Ion Trap) where these measurements are made. The cryostat design is compact and consists of a single helium bath with two vapor-cooled shields. It contains a 2-stage ADR with two magnets and two heat switches. The design of the salt pills and the complex interface between the EBIT and microcalorimeter array will be presented. We will demonstrate the performance of this new system by reporting on our latest results from this ongoing program to study these laboratory plasmas.

J05. Laboratory Astrophysics using an XRS Engineering Model Microcalorimeter

F. S. Porter ^a, P. Beiersdorfer^b, K. R. Boyce^a, G. V. Brown^a, H. Chen^b, M. Chen^b, K. C. Gendreau^a, J. Gygax^a,c, S. M. Kahn^d, R. L. Kelley^a, D. A. Liedahl^b, C. K. Stahle^a, A. E. Szymkowiak^a
aNASA/GSFC, Greenbelt, Maryland, USA
^bLawrence Livermore National Laboratory, Livermore, CA, USA
^cSwales and Associates, Beltsville, Maryland, USA
^dColumbia University, New York, NY, USA

We have recently deployed an XRS engineering model microcalorimeter at the electron beam ion trap (EBIT II) at Lawrence Livermore National Laboratory. The EBIT II can produce well defined astrophysically interesting plasmas for a wide range of plasma conditions. The XRS engineering model was mated with a 32 element XRS 6x6 microcalorimeter array and integrated into a laboratory cryostat. The system was then transported to the EBIT II for a 6 week observation campaign. The microcalorimeter array has a composite resolution of 8 eV at 1 keV and 11 eV at 6 keV. During the campaign, we performed a number of high resolution, broad band observations including: K and L shell Fe with single ionization energies from 1 - 8 keV, Maxwellian distributions of Fe with <kT> = 0.5 - 3 keV, non-equilibrium states of Fe with very fine time resolution for eta = 10⁹ - 10¹² s cm^-3. The total observation time for the campaign was over 5 Ms and the analysis is ongoing. We will present here an overview of the instrument and some of the preliminary results. The results of these experiments show the power and promise of the XRS microcalorimeter and give a detailed picture of how the instrument would have performed in orbit on Astro-E, and may perform in the future on the Astro-E2 or Joule missions.

K01. Direct Measurement of Neutrino Mass

F.Gatti
University and INFN of Genoa

The most compelling evidence of the existence for neutrino massis actually the up-down asymmetry of the atmospheric muon neutrino flux, which is interpreted on the basis of the flavor oscillation hypothesis. The flavor oscillation experiments allow a range of splitting values among the mass eigenstates that makes very attractive the investigations in the sub-eV neutrino mass range, down to 0.1 eV/c². The beta decay direct mass measurements, which are the more straightforward way for determining individual mass eigenstate, must reach such a neutrino mass sensitivity. In this frame a calorimetric experiment with Re-187, could play a starring role. Indeed a 1 eV energy resolution could be possible with a large array of small detectors. Together with the project of 1 eV resolution, 20 m long, electrostatic spectrometer for tritium beta decay (KATrin), it could be possible to fix the absolute scale of neutrino masses.

K02. Status of the RELIC Experiment

M.R. Gomes^a, P. Valko^a, TA Girard^a,
^aCentro de F�sica Nuclear,Universidade de Lisboa 1649-003 Lisbon, Portugal

The RELIC experiment is an attempt to measure the endpoint of the Re-187 electron decay spectrum with a precision of better than 2 eV, using an intrinsic detector based on the response of a planar rhenium strip immersed in a perpendicular magnetic field at 300 mK. The device operation involves measurement of the flux motion generated by the electron decay during a relaxation process, and is generally 2-3 orders of magnitude faster than bolometric techniques. We describe the detector and its current R\&D. New results, obtained by operating the device well below the magnetic field of first flux penetration, defined by the geometric barrier presence, indicate a reduction in baseline operation by a factor of 2 from previous spectra measurements

K03. Possible experiments at neutrino factories

T.O. Niinikoski^a,
^aCERN, Geneva, Switzerland

We shall explore possible experiments at high-luminosity neutrino factories which are now being planned at several laboratories. Among the proposed experiments the measurement of the nuclear coherent scattering cross section would be based on the use of calorimetric detectors segmented so that self-vetoing would supplement the surrounding muon detectors. Experiments based on new detectors, which are not time-resolved, will also be discussed. These detectors could address the dark matter problem as well.

K04. Cryogenic Detectors for Double-Beta Decay

O. Cremonesi
INFN - Sezione di Milano, I-20126 Italy

Proposed more than fifteen years ago as possible detectors for rare event searches, low temperature calorimeters (bolometers) are presently being exploited in many actual experiments. Unique aspects and possible impacts of large mass bolometers in Neutrinoless Double Beta Decay searches are summarised. A description of their operation and of the signal processing methods is also given. Presently running experiments and proposed future projects are finally reviewed.

K05. The final results of the Mi-Beta Cryogenic Experiment towards the CUORICINO Experiment.

S.Pirro, C. Arnaboldi, C. Brofferio, C. Bucci, S. Capelli, O. Cremonesi, E. Fiorini, A. Giuliani, D. McDonald, A. Nucciotti, M. Pavan, M. Pedretti, G. Pessina, C. Pobes, E. Previtali, M. Sisti, M. Vanzini, L. Zanotti
University of Milano-Bicocca

We present the final results on neutrinoless Double Beta Decay (DBD) of 130Te obtained with an array of 20 cryogenic detectors. The Mi-Beta Experiment, operating since 3 years, was upgraded in March 2001. The background in the DBD energy region was reduced by means of a new Roman lead shield framed inside the dilution unit and a neutron shield mounted outside the cryostat. We also improved the energy treshold using a cold electronic stage inside the cryostat and a double readout. The new set-up represent also a positive test for the CUORICINO Experiment. CUORICINO will start by the end of 2001 and will consist of 56 Tellurium Oxide Crystal with an overall bolometric mass of 42 kg. R\&D on CUORICINO detectors will also be presented.

K06. THE MILANO NEUTRINO MASS EXPERIMENT WITH ARRAYS OF AgReO₄ MICROCALORIMETERS

A. Nucciotti^a, C. Arnaboldi^a, C. Brofferio^a, O. Cremonesi^a, E. Fiorini^a, A. Giuliani^a, B. Margesin^b, L. Martensson^a, M. Pavan^a, G. Pessina^a, S. Pirro^a, E. Previtali^a, M. Sisti^a and M. Zen^b
a Dipartimento di Fisica ``G. Occhialini'' dell'Università di Milano-Bicocca and Sezione di Milano dell'INFN, Piazza delle Scienze 3, I-20126, Milano, Italy.
^b IRST, I-38050 Povo (TN), Italy.

We report about the Milano experiment to measure the electron antineutrino mass from the study of the ¹⁸⁷Re beta decay end-point. We present the results of the analysis of the data collected during the first measurement with an array of 10 AgReO₄ crystals. The total mass and measuring time are about 2.3 mg and 10600 hours×detector respectively, giving a total statistics of approximately 6×10^{6 187}Re beta decays. After improving the set-up a second measurement with a new array of 10 AgReO₄ crystals started and we present a preliminary analysis of the collected sample.

K07. Development of rhenium microcalorimeter for neutrino mass measurements with sensitivity in the sub-eV range.

F. Gatti, D. Pergolesi, M. Razeti, University and INFN of Genoa

The calorimetric measurement of neutrino mass in the sub-eV range is presently an appealing field of research. We are planning an experiment with higher resolution and statistics than the pilot measurement done in the last years. Such an investigation needs an array of detectors with energy resolution of few eV and rhenium mass absorber of about 0.5 mg. We present the status of the development of the array's elements which are made of composite microcalorimeters with Ag/Al TES grown on silicon substrate or directly on single rhenium crystal.

K08. KATRIN - a new tritium beta decay experiment to study the electron neutrino mass in the sub-eV range

Frank Schwamm for the KATRIN Collaboration, Forschungszentrum Karlsruhe

A precise measurement of the endpoint region of the tritium beta decay spectrum (E₀ = 18.56 keV) allows to directly determine the mass of the electron neutrino. We present a new experiment with sub-eV sensitivity, which will measure the endpoint region making use of a large electrostatic retarding spectrometer. After passing the spectrometer the decay electrons get detected by a large microcalorimeter array. The excellent resolution of such a detector makes it possible to reduce the influence of background events considerably, thus contributing to the sub-eV sensitivity.

K09. Development of cryogenic detectors for GNO

J.-C. Lanfranchi^a, F. v. Feilitzsch^a, M. Huber^a,T. Jagemann^a, J. Jochum^a, T. Lachenmaier^a, W. Potzel^a, A. Rüdig^a, J. Schnagl^a, M. Stark^a, H. Wulandari^a
aPhysik-Department E15, Technische Universität München, Munich, Germany

With a view to reducing both statistical and systematic errors in the solar neutrino experiment GNO (= Gallium Neutrino Observatory,formerly GALLEX), the miniaturized proportional counters still in use could be replaced by cryogenic detectors.The chemical extraction method which provides about ten ⁷¹Ge-atoms out of 100 tons of Galliumtrichloride represents a highly efficient procedure that must not be altered. Evidence that proportional counters (detection efficiency: 65%-75%) should be replaced by cryogenic detectors is supplied by the example of a 4pi-detector (detection efficiency: ~98%)that has been developed and tested successfully. However some modifications still have to be carried out to meet the goals set by the experimental procedure of GNO.The time window between extraction and measurement being very small due to the short half-time of ⁷¹Ge (T_1/2=11,4d)first steps have been taken to develop a detector concept comprising the possibility of independently performing the chemical deposition of Germanium via CVD (=chemical vapour deposition)onto a piece of superconducting foil and in a second step of integrating it via glueing in the detection apparatus itself.

K10. The CUORE experiment

M. Balata, C. Bucci, C. Pobes
INFN-Laboratori Nazionali del Gran Sasso, I-67010, Assergi (AQ), Italy
C. Arnaboldi, C. Brofferio, S. Capelli, L. Carbone, O. Cremonesi, E. Fiorini, D. Giugni, P. Negri, A. Nucciotti, M. Pavan, G. Pessina, S. Pirro, E. Previtali, M. Sisti, M. Vanzini and L. Zanotti
Dipartimento di Fisica dell'Universit� di Milano-Bicocca e Sezione di Milano dell'INFN, Milano I-20126, Italy
A. Giuliani and M. Pedretti
Dipartimento di Scienze Chimiche, Fisiche e Matematiche dell'Universit� dell'Insubria e Sezione di Milano dell' INFN, Como I-22100, Italy
J. Beeman^a,b, R.J. McDonald^a, E.E. Haller^a,b, E.B. Norman^a, and A.R. Smith^a
aLawrence Berkeley National Laboratory, ^bDept. of Materials Sci. and Mineral Engineering, University of California, Berkeley CA 94720, USA
M. Barucci and G. Ventura
Dipartimento di Fisica dell' Universit� di Firenze e Sezione di Firenze dell' INFN, Firenze I-50125, Italy
V. Palmieri
INFN-Laboratori Nazionali di Legnaro, Via Romea 4, I-35020 Legnaro (Padova)
G. Frossati and A. de Waard
Kamerling Onnes Laboratory, Leiden University, 2300 RAQ Leiden
F. Avignone, R.J. Creswick and H.A. Farach
Dept. of Physics and Astronomy, University of South Carolina, Columbia S.C. 29208 USA
S. Cebrian, I.G. Irastorza, A. Morales
Lab. of Nucl. and High Energy Physics, University of Zaragoza, 50009 Zaragoza, Spain

We present the CUORE (Cryogenic Underground Observatory for Rare Events) experiment, that will be composed by one thousand TeO₂ absorbers of 5×5×5 cm³ to be operated in the Gran Sasso Underground Laboratory. CUORICINO, a reduced version of CUORE, as been already approved and funded and will be in operation since the end of this year.
A detailed description of the single detector performances, of the CUORE set-up, of the cryogenic system, of the mechanical structure, and of the electronic readout will be shown.
The potentialities of CUORE will be illustrated in view of searches on rare events like double beta decay, interactions of Weakly Interacting Massive Particles (WIMPs) and solar axions, and on rare nuclear decays.

K11. Direct measurement of the L/K ratio in the electron capture decay of Be-7 with cryogenic micro-calorimeters

P.A. Voytas¹, C. Ternovan¹, M. Galeazzi², D. McCammon², J.J. Kolata³, P. Santi³, D. Peterson³, V. Guimaraes³, F.D. Becchetti⁴, M.Y. Lee⁴, T.W. Odonnel⁴, D. A. Roberts⁴, S. Shaheen^4
1Physics Department, Wittenberg University, Springfield, Ohio 45504-0720
²Physics Department, University of Wisconsin-Madison, Madison, Wisconsin 53706-1390
³Physics Department, Notre Dame University, Notre Dame, Indiana 46556-5670
⁴Physics Department, University of Michigan, Ann Arbor, Michigan 48109-1120

A good knowledge of electron capture parameters is important for certain searches for massive neutrinos, for radionuclide metrology and for other electron capture experiments. Be-7 is the lightest nucleus decaying via electron capture, with a maximum energy release (excluding the energy of the emitted neutrino) of 112~eV. This is divided between the nuclear recoil of the daughter nucleus and the energy release, in form of X-rays or Auger electrons, due to the rearrangement of the atomic shells. Due to this very low energy release, the properties of the decay have always been very difficult to study and the L/K ratio has never been measured. Cryogenic micro-calorimeters, thanks to their good energy resolution and equal sensitivity to different kind of radiation, are the perfect instrument for such measurements. We report here the observation of the Be-7 electron capture made with cryogenic micro-calorimeters composed by HgTe absorbers in which the radioactive nucleus was embedded and Si implanted thermistors. With an energy resolution of 8.5 eV FWHM we have been able to separate the different features of the decay energy spectrum, leading to the first direct exploration of the L/K ratio in Be-7.

L01. Results and Plans of CRESST Dark Matter Search

C. Cozzini for the CRESST collaboration ^a,
^a Max-Planck-Institut für Physik, Munich, Germany

Results of the CRESST experiment at Gran Sasso using 262g sapphire calorimeters with tungsten phase transition thermometers are presented. We report on improvements of the detector performance and the reduction of background and discuss the calibration. Data taken in 2000 have been used to place limits on WIMP dark matter particles in the galactic halo. The sapphire detectors are especially sensitive for low-mass WIMPS with spin-dependent interaction and improve on existing limits in this region. CRESST is now preparing for a second phase, which will use 300 g CaWO4 crystals with coincident detection of phonons and scintillation light to suppress the radioactive background.

L02. Latest results from the Cryogenic Dark Matter Search

T.A. Perera^a, R. Abusaidi^h, D.S. Akerib^a, P.D. Barnes, Jr.ⁱ, D.A. Bauer^j, A. Bolozdynya^a, P.L. Brink^h, R. Bunker^j, B. Cabrera^h, D.O. Caldwell^j, J.P. Castle^h, R.M. Clarke^h, P. Colling^h, M.B. Crisler^b, A. Cummingsⁱ, A. Da Silvaⁱ, A.K. Davies^h, R. Dixon^b, B.L. Dougherty^h, D. Driscoll^a, S. Eichblatt^b, J. Emes^c, R.J. Gaitskellⁱ, S.R. Golwala⁹, D. Hale^j, E.E. Haller^c, J. Hellmigⁱ, M.E. Huber^k, K.D. Irwin^d, J. Jochumⁱ, F.P. Lipschultz^g, A. Lu^j, V. Mandicⁱ, J.M. Martinis^d, S.W. Nam^d, H. Nelson^j, B. Neuhauser^g, M.J. Penn^h, M.C. Perillo Isaacⁱ, B. Pritychenkoⁱ, R.R. Ross^3,9, T. Saab^h, B. Sadoulet^3,9, R.W. Schnee¹byline, D.N. Seitzⁱ, P. Shestople^g, T. Shutt^e, A. Smith^c, G.W. Smithⁱ, G.W. Smithⁱ, A.H. Sonnenschein^j, A.L. Spadaforaⁱ, W. Stockwellⁱ, J.D. Taylor^c, S. Whiteⁱ, S. Yellin^j, B.A. Young^f
aDepartment of Physics, Case Western Reserve University, Cleveland, OH 44106, USA
^bFermi National Accelerator Laboratory, Batavia, IL 60510, USA
^cLawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
^dNational Institute of Standards and Technology, Boulder, CO 80303, USA
^eDepartment of Physics, Princeton University, Princeton, NJ 08544, USA
^fDepartment of Physics, Santa Clara University, Santa Clara, CA 95053, USA
^gDepartment of Physics and Astronomy, San Francisco State University, San Francisco, CA 94132, USA
^hDepartment of Physics, Stanford University, Stanford, CA 94305, USA
ⁱCenter for Particle Astrophysics, University of California, Berkeley, Berkeley, CA 94720, USA
^jDepartment of Physics, University of California, Santa Barbara, Santa Barbara, CA 93106, USA
^kDepartment of Physics, University of Colorado, Denver, CO 80217, USA

The Cryogenic Dark Matter Search (CDMS) uses cryogenic detectors to search for WIMPs via their elastic-scattering interactions with nuclei. The latest results from CDMS I using simultaneous measurement of phonons and charge in semiconductor targets will be presented. These data give limits on the spin-independent WIMP-nucleon elastic-scattering cross section that exclude previously unexplored parameter space above 10 GeV ^-2. This is a new instance of cryogenic detectors surpassing the sensitivity of conventional technologies. Recent work on understanding the nature of limiting backgrounds and progress in data analysis will be presented. The second generation experiment (CDMS II) located at a deep site will also be described.

L03. Dark Matter Search in the EDELWEISS experiment

D. Drain^a, A. Benoit^b, L. Berge^c, A. Bonnevaux^a, R. Bouvier^a, A. Broniatowski^c, B. Chambon^a, M. Chapellier^d, G. Chardin^e, P. Charvin^e,f, P. Cluzel^a, M. De Jesus^a, P. Di Stefano^e, L. Dumoulin^c, J. Gascon^a, G. Gerbier^e, C. Goldbach^g, M. Goyot^a, M. Gros^e, J. P. Hadjout^a, A. Juillard^e, A. de Lesquen^e, D. Loiseau^e, J. Mallet^e, S. Marnieros^c, O. Martineau^a, N. Mirabolfathi^c, L. Mosca^e, X-F. Navick^e, G. Nollez^g, P. Pari^d, M. Stern^a, L. Vagneron^a
dIPN Lyon and UCBL, IN2P3-CNRS, 43 Bd. 11 novembre 1918, F-69622 Villeurbanne Cedex, France
^bCentre de Recherche sur les Tres Basses Temperatures, BP 166, 38042 Grenoble, France
^cCSNSM, IN2P3-CNRS, Univ. Paris XI, bat. 108, F-91405 Orsay Cedex, France
^dCEA, Centre d'Etudes Nucleaires de Saclay, DSM/DRECAM, F-91191 Gif-sur-Yvette, France
^eCEA, Centre d'Etudes Nucleaires de Saclay, DSM/DAPNIA, F-91191 Gif-sur-Yvette, France
^fLaboratoire Souterrain de Modane, CEA-CNRS, 90 rue Polset, F-73500 Modane, France
^gInstitut d'Astrophysique de Paris, INSU-CNRS, 98 bis Bd. Arago, F-75014 Paris, France

The results obtained in the EDELWEISS-I experiment using 320g bolometers with simultaneous ionization and heat measurements are presented. The analysis of data accumulated in November and December 2000 with one of these detectors already excludes the upper part of the DAMA WIMP's region. This result is obtained without neutron background subtraction and corresponds to a background rejection factor of ~ 99.9 %. Prospects and preliminary results of the present 1kg stage are presented. The second stage of the EDELWEISS experiment will operate an innovative reversed cryostat housing about 100 detectors. A brief report is given on the milestones of this experiment.

L05. Scintillation light and phonon measurement based on Ir/Au-thermometers

M. Stark^a, F. v. Feilitzsch^a, M. Huber^a, T. Jagemann^a, J. Jochum^a, T. Lachenmaier^a, J.-C. Lanfranchi^a, W. Potzel^a, A. Rüdig^a, J. Schnagl^a, H. Wulandari^a
aPhysik-Department E15, Technische Universität München, Munich, Germany

With the simultaneous measurement of the temperature signal of a CaWO₄ absorber crystal and the scintillation light, it is possible to reject the gamma and electron background. We report on an alternative new light detector design for the CRESST experiment. For the light detector we use iridium/gold phase transition thermometers with a special circular structure and an Al phonon collector on a silicon substrate. With this detector an energy threshold of 22.1 eV on a 5sigma level was achieved. The light detector was tested in coincidence with a phonon measurement of a 300 g CaWO₄ crystal. The phonons from the CaWO₄ crystal were measured with an Ir/Au thermometer with a transition temperature of 32 mK.

L06. Update on the CDMS SUF Runs

Tarek Saab, on behalf of the CDMS collaboration

The current (2001) CDMS data run is the last at the SUF shallow site before operations at the Soudan deep site begin next year. For the 2001 run CDMS has deployed one tower of 6 ZIPs, 3 Ge (0.75 kg) and 3 Si (0.30 kg), which will be transported to Soudan as soon as the site is operational. This presentation will report on the latest results from the run as well as summarizing the final results from the 2000 SUF run.

L07. Development of 300 g scintillating calorimeters

T. Frank^a, G. Angloher^b, C. Cozzini^a, M. Bruckmayer^a, D. Hauff^a, P. Di Stefano^a, F. Pr�bst^a, W. Seidel^a,
^aMax-Planck-Institut fuer Physik, Munich, Germany
^bUniversity of Oxford, United Kingdom

The sensitivity for WIMP detection can be improved by an ability to efficiently discriminate the gamma and beta backgrounds from the nuclear recoil signals. The CRESST phase II detectors will achieve this discrimination by means of simultaneous measurement of phonons and scintillation light. We report on the development of a 300g detector module consisting of two separate calorimeters fitted with tungsten phase transition thermometers. A 300g CaWO4 crystal serves as the target material in which a recoiling WIMP creates both, phonons and scintillation light. Phonons are detected by a thermometer on the CaWO4 crystal. A second smaller detector in close proximity detects the scintillation light. Measurements with this setup will be presented.

L08. Discrimination performances and design of 320g ionization-heat bolometers for the EDELWEISS experiment

X-F. Navick ^a, M. Chapellier^b, J. Gascon ^c, A. Juillard ^a, O. Martineau ^c, EDELWEISS Collaboration
^aDAPNIA/SPP, Centre d'Etudes de Saclay, F-91191 Gif-sur-Yvette Cedex, France
^b DRECAM/SPEC, Centre d'Etudes de Saclay, F-91191 Gif-sur-Yvette Cedex, France ^c IPNLyon-UCBL, IN2P3-CNRS, 4 rue Enrico Fermi, 69622 Villeurbanne Cedex, France

The performances of the 320g ionization�heat bolometers developed for the EDELWEISS experiment and installed in the Underground Laboratory of Modane are described. Analysis of the data demonstrates that a level of discrimination as high as 99.9% can be achieved above 30 keV recoil energy in real data taking conditions between nuclear recoils and radioactive background. The holder design and the procedures followed to reduce the radioactive background, in particular for betas and low energy X-rays, will be presented. By improving the fabrication technique, we have obtained the same sensitivity for the heat channel with 320g detectors than with previous 70g detectors. The use of two ionization channels, defining a guard ring and a central volume, has shown a significant improvement in the discrimination performances of the detectors and will be discussed.

L09. Position Information in the CDMS II ZIP detectors

V. Mandic^a, P. Meunier^b, W. Rau^c, P. Brink^d, and CDMS Detector Group^e,
^aUC Berkeley
^bUC Berkeley
^cUC Berkeley
^dStanford University
^eCase Western Reserve University, Santa Clara University, Stanford University, and University of California at Berkeley

The Ge and Si detectors developed by the CDMS II experiment rely on the simultaneous detection of athermal phonons and ionization produced by interactions in the crystal. The athermal phonons not only provide the total energy deposited during an interaction, but also carry information about the position of the interaction. In this paper we will describe how this information can be extracted using the pulse shapes in the four phonon sensors. In particular, we will present the result of measurements made on detectors from the first CDMS II production batch. We will also investigate ways of using the event position information to extract further information about the phonon signal and about the sensor itself.

L10. Amorphous Silicon Ionization Contacts on Germanium and Silicon

T. Shutt^a, B.Sadoulet^b, P. Brink^c, and the CDMS detector group (Case Western Reserve U., Santa Clara U.,Stanford, U.C. Berkeley)
^aPrinceton University, Princeton, NJ
^bUniversity of California at Berkeley, Berkeley, CA
^cStanford University, Stanford, CA

By simultaneously sensing phonons and ionization, the CDMS detectors are able to distinguish between nuclear and electronic recoils. This strategy, an essential element of the search for Weakly Interactive Massive Particles in the halo of our galaxy, is defeated if ionization is badly measured. In particular, for the correct identification of low-energy electrons incident on the surface, it is important to minimize the ionization deficit close to the contacts. Such dead regions are due to the back diffusion of charge carriers to the contact. In this poster, we will summarize the experimental results obtained with a 300 Angstrom amorphous silicon layer deposited on the bulk germanium or silicon. The amorphous layer is itself covered by a thin aluminum Shottky contact. In the measurement of the ionization signal from slow electrons incident on the surface, we observe significant improvement compared to the implanted or Shottky contacts that we previously used. This is presumably due to the higher gap of amorphous silicon, which reflects the carriers back to the bulk. Moreover, such a layer provides a convenient etch stop that enables the transfer of silicon photolithographic processes to germanium.

L11. Identification of near-surface events in massive bolometers

N. Mirabolfathi^a, L. Berge^a, L. Dumoulin^a, S. Marnieros^a
a CSNSM, IN2P3-CNRS, Univ. Paris XI, bat. 108, F-91405 Orsay Cedex, France

The identification of surface events in massive detectors is essential for several physics applications. For charge detectors, it would allow a significant improvement of the peak over background ratio. For dark matter applications, it would greatly increase the discrimination performances of the ionization-heat detectors, which represent now the best WIMP detectors. Using NbSi Anderson insulator thermometric layers as electrodes, the athermal phonon signal trapped in the thermometer has been shown to present a factor 4 enhancement for interactions occurring close to the thermometric layers. Using alpha, beta and gamma radioactive sources on bulk sapphire and germanium detectors, we have determined the correlation between the athermal pulse height and the interaction depth. This method already allows the identification of surface events down to an energy of a few keV and may represent a dramatic improvement on the rejection performances of Dark Matter detectors.

L12. Event localization and space-charge characterization in low-temperature germanium detectors for the Edelweiss dark-matter experiment

A. Broniatowski, A. Juillard, L. Berg�, and L. Dumoulin
Centre de Spectrom�trie Nucl�aire et de Spectrom�trie de Masse

An improved pulse shape analysis of the ionization signals is presented to identify near-surface events in guarded-ring germanium detectors for the Edelweiss dark matter experiment (ref. [1]).The same analysis provides a sensitive check for space-charge build-up, a key issue for proper operation of the detectors. [1] Electronic Transport and Event Localization in Germanium Low-Temperature Detectors for the Edelweiss Dark Matter Experiment, Proc. LTD8 in Nucl. Instr. and Meth. A 444, 327 (2000).

L13. Investigation of superconducting phase transition thermometers as phonon sensors for ionization-phonon detectors in the EDELWEISS dark matter search experiment

M. Loidl^a, L. Berge^b, L. Dumoulin^b,
^aCEA, Centre d'Etudes Nucleaires de Saclay, DSM/DAPNIA, F-91191 Gif-sur-Yvette, France
^b CSNSM, IN2P3-CNRS, Univ. Paris XI, bat. 108, F-91405 Orsay Cedex, France

The EDELWEISS collaboration is using ionization-phonon Ge detectors, allowing discrimination of electron and nuclear recoil events, for WIMP dark matter search. We are exploring the potential of superconducting phase transition thermometers to replace the NTD germanium phonon sensors used up to now. Apart from an expected improvement of energy resolution and threshold of the phonon channel, this sensor type could facilitate the fabrication of a large number of detectors for a large scale dark matter search experiment. Additionally, it might offer a way for event localization in view of the rejection of surface events, which can mimic nuclear recoil events due to incomplete charge collection. First results will be presented.

L14. Neutron Scattering Facility for the Calibration of The Response to Nuclear Recoils

J.Jochum^a, B.Chambon^b, D.Drain^b, F.von Feilitzsch^a, J.Gascon^b, M.Huber^a, T.Jagemann^a, M.De Jésus^b, T.Lachenmaier^a, J.-C.Lanfranchi^a, O.Martineau^a, W.Potzel^a, A.Rüdig^a, J.Schnagl^a, E.Simon^b, M.Stark^a, M.Stern^b, H.Wulandari^{a a} Physik Department E15, Technische Universität München, Munich, Germany ^b Institut de Physique Nucléaire de Lyon, Lyon, France

A possibility to search for elementary particles as dark matter candidates is to detect elastic scattering on target-nuclei with cryogenic detectors. For the interpretation of the data on has to calibrate the detector response to nuclear recoils. The ratio between this response and the response to gammas of the same energy is known as the quenching factor. With cryogenic detectors capable to background discrimination the quenching factors for the heat- and for the scintillation- or ionization-measurement could be different for different target nuclei. They can be measured by scattering of neutrons. The CRESST- and the EDELWEISS-collaborations have set up a neutron scattering facility for cryogenic detectors at the tandem-accelerator of the Munich 'Maier-Leibniz-Labor'. The goal is to determine the quenching factors for Germanium detectors, on Al and O in Sapphire detectors, and on O, Ca and W in CaWO₄ detectors. The scattering angle and the time-of-flight of the neutrons is measured by an array of liquid scintillator cells. The pulsed high energy (12MeV) neutron beam is created by nuclear reaction of a ¹¹B on a H-gas target. The set-up and the results of first tests will be presented.

L15. Determination of the Tc distribution for a 1000 TESs

P.L. Brink for the CDMS collaboration^*, and A.J. Miller^a.
^*D.S. Akerib, A. Bolodyznya, D. Driscoll, T.A. Perera, R.W. Schnee from Case Western Reserve University; M.B. Crisler, R. Dixon, S. Eichblatt, D. Holmgren from Fermi National Accelerator Laboratory; J. Emes, E.E. Haller, R.R. Ross, A. Smith, J.D. Taylor from Lawrence Berkeley National Laboratory; K.D. Irwin, J.M. Martinis, S.W. Nam from National Institute of Standards and Technology; T. Shutt from Princeton University; B.A. Young from Santa Clara University; F.P. Lipschultz, B. Neuhauser, P. Shestople from San Francisco State University; R. Abusaidi, P.L. Brink, B. Cabrera, J.P. Castle, C. Chang, R.M. Clarke, P. Colling, A.K. Davies, B. Dougherty, M. Penn, T. Saab from Stanford University; P.D. Barnes, Jr., A. Cummings, A. Da Silva, R.J. Gaitskell, S.R. Golwala, J. Hellmig, J. Jochum, V. Mandic, P. Meunier, M.C. Perillo-Isaac, B. Pritychenko, B. Sadoulet, D.N. Seitz, G.W. Smith, A.L. Spadafora, W. Stockwell, S. White from University of California at Berkeley; D.A. Bauer, R. Bunker, D.O. Caldwell, D. Hale, C. Maloney, H. Nelson, J. Sander, A.H. Sonnenschein, S. Yellin from University of California at Santa Barbara; M.E. Huber from University of Colorado.
^aDepartment of Physics, Stanford University, Stanford , CA 94305

The ZIP detectors deployed in the CDMS II experiment utilize phonon sensors comprising W Transition Edge Sensors (TESs). In order to ensure uniform collection of the athermal phonon signal the TESs are dispersed uniformly on one side of a 1 cm thick, 3 inch diameter, disk. Each quadrant contains 1036 TESs connected in parallel to one series-array SQUID amplifier. The initial transition temperatures of these TESs tend to be too high for our requirements, and substantial gradients make the operation of the detectors difficult. Thus the implementation of Fe-56 ion implantation, as reported at the previous LTD meeting, to reduce in a controlled manner the transition temperature. However, the successful implementation of this ion-implantation scheme requires accurate knowledge of the initial transition temperature of each TES in a given quadrant. We will report on our approaches and techniques employed to address the issue of determining the initial Tc distribution.

L16. A Testing Strategy for the Mass Production of CDMS II Detectors

D. Driscoll^a, P. Meunier^c,
R. Abusaidi^b, D. Abrams^b, D.S. Akerib^a, M.S. Armel^c, L. Badis^c, P.D. Barnes, Jr.^c, D. Bauer^b, A. Bolozdynya^a, P.L. Brink^b, B. Cabrera^b, D. Caldwell^b, J.P. Castle^b, C. Chang^b, R.M. Clarke^b, P. Colling^b, A. Cummings^c, A. Da Silva^c, R.J. Gaitskell^c, S.R. Golwala^c, J. Hellmig^c, J. Jochum^c, S. Kamat^a, V. Mandic^c, A. Miller^b, M.J. Penn^b, T.A. Perera^a, M.C. Perillo Isaac^c, B. Pritychenko^c, W. Rau^c, R.R. Ross^c, T. Saab^b, B. Sadoulet^c, R.W. Schnee^a, D.N. Seitz^c, G.W. Smith^c, A.L. Spadafora^c, G. Wang^a, S. White^c,
^aDepartment of Physics, Case Western Reserve University, Cleveland, OH 44106, USA.
^bDepartment of Physics, Stanford University, Stanford, CA 94305, USA.
^cCenter for Particle Astrophysics, University of California, Berkeley, Berkeley, CA 94720, USA.

The Cryogenic Dark Matter Search (CDMS) employs detectors which are capable of simultaneously measuring the ionization and phonon energies deposited by a particle collision. These detectors are 1-cm-thick, 7-cm-diameter crystals of either germanium or silicon with a thin film of aluminum and tungsten patterned on the surface. This presentation discusses the testing regimen that a typical CDMS detector undergoes before it gets approval for final installation at the CDMS II deep side in Soudan, MN which should be coming online within a year. Now that our technology is relatively stable, the main focus of our test facilities is to provide quality control for the mass production of our detectors. First, the critical temperatures of the tungsten and other basic quantities are measured in preparation for iron implantation, which will bring the T_c down to the desired range (~70 mK). The same basic measurements are taken again after implantation to assure that the correct T_c was achieved. Finally, a detailed map of energy response as a function of position is made to make sure that there are no inhomogeneities across the surface.

M01. Progress Report on Transition-Edge Sensors for Optical/UV Astronomy

A. J. Miller^a, S. W. Nam^a, B. Cabrera^b, R. W. Romani^b, P. Brink^b, J. P. Castle^b
aNational Institute of Standards and Technology, Boulder, CO
^bStanford University, Stanford, CA

Cryogenic particle detectors are showing great promise for use in faint-object optical/UV astronomy. Our detectors are superconducting Transition Edge Sensors (TESs) that have been designed for photon counting in the energy (wavelength) range of 0.5eV (2.5µm) to 10eV (124nm). These devices have the demonstrated ability to simultaneously measure photon energy and time-of-arrival at count rates exceeding 15Kcts/s/pixel. Each photon is time-tagged to 0.4us using a GPS signal processor, and the energy is determined to ~0.15eV FWHM. We summarize the operation and single-pixel performance of these devices and present results from our application of the sensors to observational astronomy using the 2.7m telescope at the McDonald Observatory in Texas. We also summarize our progress toward a 32-pixel focal-plane array of TES devices. We discuss the TES array design, SQUID readout, and the cryogenic apparatus. We also summarize the optical design including a cryogenic focusing system and blackbody-radiation filters.

M02. A 12x10 Pixels Superconducting Tunnel Junction Array for Optical Astronomy

D.D.E. Martin^a, P. Verhoeve^a, A. Peacock^a, A. van Dordrecht^a
aSpace Science Department of the European Space Agency, ESTEC, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands

Superconducting Tunnel Junctions (STJs) have been extensively investigated as photon detectors covering the range from near- infrared to X-ray energies. A 6x6 array of Tantalum junctions has already been used in an optical spectro-photometer. With this camera, the European Space Agency has performed multiple astronomical observations of optical sources using the William Herschel 4.2m telescope at La Palma. Following the success of this programme, we are now developing a second generation camera. The goals of this programme are: increase the field of view of the instrument from 3.6"x3.6" to 10.5"x9" optimise infrared rejection filters, possibly extending the 'red' response to ~1um wavelength increase the electronic's readout speed For these purposes, we are developing a new Superconducting Tunnel Junction Array consisting of 10x12 Tantalum/Aluminium devices as well as an improved readout system. In this paper, we review the instrument's architecture and describe the performance of the new detector. In addition, results related to device yield based on the reproducibility of low leakage devices will be presented. Finally, we shall review the detectors' responsivity and uniformity thereof as well as the achieved energy resolution.

M03. The millimeter-wave properties of superconducting microstrip lines

A. Vayonakis, C. Luo, H.G. Leduc, J. Zmuidzinas

We have developed a novel technique for making high quality measurements of the millimeter-wave properties of superconducting thin-film microstrip transmission lines. Such microstrip lines are currently used for tuning circuits in SIS mixers and pulse propagation in RSFQ superconducting digital electronics. In addition, microstrip lines have been proposed for use in millimeter and submillimeter direct detection applications, e.g. for on-chip filters. Our experimental technique, which currently covers the 75-110 GHz band, is robust and can be easily extended to higher frequencies. The method is based on standing wave resonances in an open ended transmission line. The entire circuit is fabricated on a thick silicon substrate, and the millimeter-wave radiation is coupled onto the chip quasioptically. Two SIS junctions serve as direct detectors: one to monitor the incident power, and one to measure the resonances. Our data for Nb/SiO/Nb lines, taken at 4.2 K and 1.6 K, can be explained by a single set of physical parameters. Our preliminary conclusion is that the loss is dominated by the SiO dielectric, with a temperature-independent loss tangent around 0.005 for our samples.

M04. Z-Spec: A Redshift Machine for Dusty Submillimeter Galaxies

J. Glenn CASA, University of Colorado, Boulder, CO J.J. Bock, M. Dragovan, H. Nguyen Jet Propulsion Laboratory, Pasadena, CA C.M. Bradford, J.J. Gromke, B.J. Naylor, J. Zmuidzinas California Institute of Technology, Pasadena, CA H. Matsuhara Institute of Space and Astronautical Science, Sagamihara, Japan

An extragalactic, far-infrared background radiation with integrated power nearly equal to the integrated optical starlight in the universe was discovered by NASA's Cosmic Background Explorer. Ongoing and imminent submillimeter surveys are resolving this background, generated by embedded star formation and accretion onto supermassive black holes, into individual galaxies. Catalogs of these submillimeter galaxies promise to provide a unique probe of star formation, nuclear activity, and structure formation in the universe. However, it has been very difficult to assign optical counterparts to submillimeter galaxies to measure redshifts due to the large, diffraction-limited submillimeter beams. We are building a broadband millimeter-wave spectrometer, Z-Spec, to measure redshifts using emission lines of carbon monoxide. Z-Spec is comprised of a waveguide-coupled diffraction grating that disperses radiation onto an array of 150 100-millikelvin silicon nitride micromesh bolometers.

M05. CALOS: an Experiment to Study the Solar Corona with an Array of NTD Germanium Microcalorimeters

M. Barbera^a, G. Peres^a, S. Orlando^a, F. Reale^a, A. Collura^a, S. Serio^a, E. Silver^b, S. Bandler^b, H. Schnopper^b, E. Costa^c, R. Bellazzini^d
aOsservatorio Astronomico di Palermo G.S. Vaiana, Palermo, Italy
^bSmithsonian Astrophysical Observatory, Cambridge MA, USA
^cIstituto di Astrofisica Spaziale (CNR), Rome, Italy
^dIstituto Nazionale di Fisica Nucleare, Pisa, Italy

In response to the Italian Space Agency announcement ''New ideas for Space Missions'', we have proposed to build and operate an observatory ''CALorimetri per Osservazioni Solari'' (CALOS) that will perform spatially resolved (Delta theta ~ 2') X-ray spectroscopy of the solar corona over the 0.1 - 10 keV band using an array of NTD germanium microcalorimeters. While X-ray spectroscopy of the solar corona has been performed in the past for small regions of the corona and/or narrow parts of the X-ray spectrum, this observatory will produce spectroscopic images of the entire corona simultaneously. The pin hole camera we propose works as a very low cost imaging optic and maintains the count rate at the level adequate for the calorimeters. The observatory will include a hard X-ray polarimeter of radically new design that will serve as a flare alarm and will study the hard X-ray solar emission and its polarization.

M06. High resolution spectroscopy of the X-ray emission of GRB's by IMXS

L. Piro^a, L. Colasanti^a, E. Costa^a, P. Soffitta^a, A. De Rosa^a, F. Gatti^b, F. Fontanelli^b,M. Galeazzi^b, P. Fabbricatore^c, S. Farinon^c, A. Ferrari^d, E. Trussoni^d, M. Orio^d, D. Mc Cammon^e, T. Sanders^e, M. Galeazzi^e, A. Szymkowiak^f, S Porter^f
aIstituto Astrofisica Spaziale, CNR, Rome, Italy
^b Universita' Genova, Italy
^c INFN Genova, Italy
^d Oss. Astronomico Torino, Italy
^e Wisconsin University, Madison
^f GSFC/ NASA

The Intergalactic and interstellar Medium X-Ray Survey is an experiment based on X-ray bolometers proposed to fly on the ISS, inorder to perform an all-sky X-ray survey with high spectroscopic resolution in the 0.1-8 keV range. We expect that several GRB will be detected during the mission lifetime. In a few cases we will have enough statistics to perform high resolution spectroscopy of the prompt X-ray emission. Here we will describe the performances of the experiment in this field.

M07. The Astro-E Mission - Past, Present and Future

R.L. Kelley, NASA/Goddard Space Flight Center, Greenbelt, MD, USA
K. Mitsuda, Institute of Space and Astronautical Science, Sagamihara, Japan

The Japan/US Astro-E mission was to provide astrophysicists with broadband, high-resolution x-ray spectroscopy with high sensitivity for the study of complex phenomenon from a wide variety of celestial x-ray sources. A failure of the launch vehicle prevented the observatory from reaching orbit in February 2000. The unique features of Astro-E, particularly those of the microcalorimeter x-ray spectrometer (XRS), were designed to complement the spectroscopic capabilities of the Chandra and XMM observatories now in orbit. The energy resolution of 12 eV in a 32 pixel array would have enabled powerful diagnostics of high energy processes from measurements of L- and K-shell atomic transitions, including dynamical information, to be determined with high precision. The instrument incorporated a three stage cooling system capable of operating the microcalorimeter array at 0.060 K for about two years in orbit. The scientific goals of the Astro-E mission remain timely and the implementation of the instrumentation is still viable. We will review the Astro-E microcalorimeter/cryogenic system, the scientific capabilities of Astro-E, and the efforts underway to rebuild the observatory.

M08. X-Ray and Gamma-Ray Astronomy with NTD Germanium-based Microcalorimeters: Progress Toward Plasma Diagnostics and Nuclear Line Observations

E. Silver^a, S. Bandler^a, H. Schnopper^a, S. Murray^a, N. Madden^b, D. Landis^b, J. Beeman^b, E. E. Haller^b, M. Barbera^c
aHarvard-Smithsonian Center For Astrophysics, Cambridge, MA
^bLawrence Berkeley National Laboratory, Berkeley, CA
^cOsservatorio Astronomico G.S. Vaiana, Palermo, Italy

The success of future astrophysics missions devoted to high resolution x-ray and gamma-ray spectroscopy is dependent on the spectral imaging performance of large field-of-view microcalorimeter arrays. High energy resolution and broad bandwidth are required so that powerful diagnostic line ratios and detailed study of line shapes can be used to establish the physical conditions in the source. High throughput and low internal background are important so that our modeling is constrained by the physics rather than the statistics. This is especially true for gamma-ray observations. We report that our NTD-Ge microcalorimeters have the sensitivity (instantaneous signal to noise ratio) to detect 6 keV x-rays with a resolution of 2 eV, and the sensitivity to detect 60 keV gamma-rays with a resolution less than 35 eV. To date, our actual measured spectral resolution on x-ray and gamma-ray lines from radioactive sources and laboratory plasmas is currently slightly worse than these values (4.8 eV throughout the 1 - 6 keV band and 52 eV at 60 keV, respectively). Technical details responsible for this performance will be presented as well as an innovative electro- thermal approach for significantly enhancing count-rate capability. A prototype 3 x 10 element focal plane array has been constructed and is undergoing tests. We will discuss the results.

M09. High resolution X-Ray Spectroscopy of Gamma-ray Bursts

L. Piro ^a
aIstituto Astrofisica Spaziale, CNR, Rome, Italy

The discovery of iron absorption and emission lines in the X-ray spectra of Gamma-Ray Bursts (GRB) has opened new areas of investigations, that go beyond the specific field of GRB. I will briefly summarize the observations of X-ray features in GRB by BeppoSAX \& Chandra, and their implications on the origin of these powerful explosions, the largest after the Big Bang. I will then describe the prospects in using GRB as cosmological beacons of the early and near Universe, by high-resolution X-ray spectroscopy with future missions, like IMXS, Next Generation GRB Observatory \& XEUS.

M10. Superconducting Tunnel Junction Detectors for Ground-based Optical astronomy and Space-based UV and X-ray Astrophysics

Peter Verhoeve Space Science Department, European Space Agency, ESTEC, Noordwijk, The Netherlands

Superconducting tunnel junctions (STJs) combine intrinsic energy resolution, good detection efficiency and high responsivity, thus providing energy resolved photon counting performance in a wide energy range. In particular, for optical astronomy STJs offer >60% detection efficiency throughout the UV/Visible, high speed (~10⁴ cts/s), good time resolution (~microseconds), with modest resolving power (~20). In the X-ray range their resolving power is such that these detectors could replace relatively inefficient wavelength dispersive elements. An overview is presented of the STJ development within the Space Science Department of ESA. The spectroscopic performance of Ta-based single STJs, small arrays and STJ-absorber structures in the UV-NIR and X-ray bands is discussed. As a first application S-Cam is described: a cryogenic camera for ground-based optical astronomy exploiting a 6x6 array of Ta STJs. This camera has undergone four campaigns at the 4.2m William Herschel Telescope at La Palma (Spain), and future camera generations are under development. For the soft X-ray band (50-3000eV) a STJ-based instrument with a 7x7mm² active area is proposed as part of the X-ray Evolving Spectroscopy Mission (XEUS), which is currently under study at ESA. Future developments include devices from lower Tc superconductors for improved energy resolution, and larger format arrays combined with alternative read-out schemes.

M11. TES Spectrophotometers for Near IR/Optical/UV

B. Cabrera Stanford University

A review of recent progress and future prospects for superconducting transition-edge sensor (TES) spectrophotometers from the near infrared through ultraviolet bands. These instruments time-stamp and energy-resolve each photon with high efficiency. Comparisons are made between the superconducting tunnel junction (STJ) detectors and the TES detectors, as well as a summary of existing detector technologies and their capabilities. Applications include compact object and extremely faint ground-based and satellite-based astrophysics, and biomolecular florescence spectroscopy.

M12. Use of high sensitivity bolometers for astronomy: The Planck case

J. M. Lamarre^a,
^aInstitut d'Astrophysique Spatiale, Orsay, France

The Planck satellite is a project of the European Space Agency based on a wide international collaboration, including United States and Canadian laboratories. It is dedicated to the measurement of the anisotropy of the Cosmic Microwave Background (CMB) with unprecedented sensitivity and angular resolution. Its High frequency Instrument (HFI) is based on the use of bolometers cooled down to 100mK. The sensitivity will be limited by the photon noise of the CMB itself at low frequencies, and of the instrument background at high frequencies. The requirements on the measurement chain are directly related to the strategy of observation used for the satellite. This impacts the bolometer design as well as other elements: The cooling system must present outstanding temperature stability, and the amplification chain must show a flat noise spectrum down to very low frequencies. Requirements are efficiently expressed in the Fourier domain. In the same way, the detector layout in the HFI is closely related to the scanning strategy. A tentative generalization of the results of Planck-HFI to astronomical observations will be presented, with some conclusion on ideal future detectors.

M13. SCUBA 2 - a wide field camera for the James Clerk Maxwell Telescope

William Duncan (UKATC) Wayne Holland (") Edward Ian Robson (Joint Astronomy Centre, Hilo, HI 96720, USA) Kent Irwin (NIST, Boulder, Co) Gene Hilton (") Anthony J Walton (The Scottish Microelectronics Centre, Edinburgh EH9 3JF, UK)

SCUBA 2 will employ multiplexed arrays of TES sensors to increase the speed of measurement of the JCMT at sub mm wavelengths by several orders of magnitude. We describe the requirements the scientific goals impose on the array and instrument design. We will describe the arrays and illustrate some of the problems posed to the detector design by the high and variable atmospheric background experienced in submm ground-based astronomy. We will outline the rest of the SCUBA 2 project.

M14. Central Questions in Cosmology and Low Temperature Detectors

Bernard Sadoulet
University of California, Berkeley,CA

I propose to review some of the most central questions of cosmology and indicate how cryogenic detectors can contribute to their solution. My remarks could be structured around four themes
o Dark Matter: Direct Detection, Cosmic Microwave Background anisotropy, Mapping of clusters with x ray and Sunyaev-Zel'dovich
o Dark Energy: Cosmic Microwave Background anisotropy, Cluster surveys with Sunyaev-Zel'dovich
o Structure formation: study of the dark ages in millimeter waves, role of Massive Black Holes, warm baryons
o The origins: Inflation and primordial gravitational wave background. Cosmic Microwave Background polarization.
I would attempt to indicate the specific role that low temperature detectors could play and how they are complementary to other technologies.

M15. BLAST - A Balloon-borne Large Aperture Sub-millimeter Telescope

J. Gundersen^a, P. Ade^b, J. Bock^c, P. DeBernardis^d, M. Devlin^e, M. Griffin^b, M. Halpern^f, D. Hughes^g, J. Klein^e, S. Masi^d, P. Mauskopf^b, B. Netterfield^h, L. Olmiⁱ, D. Scott^f, G. Tucker^j
aUniversity of Miami, Coral Gables, FL
^bCardiff University, Cardiff, UK
^cJet Propulsion Laboratory, Pasadena, CA
^dUniversity of Rome, Rome, Italy
^eUniversity of Pennsylvania, Philadelphia, PA
^fUniversity of British Columbia, Canada
^gINAOE, Puebla, Mexico
^hUniversity of Toronto, Toronto, Canada
ⁱUniversity of Massachusetts, Amherst, MA
^jBrown University, Providence, RI

The Balloon-borne Large Aperture Sub-millimeter Telescope (BLAST) incorporates a 2- meter primary mirror with large-format bolometer arrays consisting of 149, 88, and 43 elements operating at 250, 350 and 500 µm, respectively. The combination of the dramatically increased atmospheric transmission at balloon altitudes and the extended observing time (10-20 days) afforded by a long duration balloon flight will enable the first sensitive, large-area (gg10 deg²) sub-mm surveys at these wavelengths. These surveys will address some of the most important galactic and cosmological questions regarding the formation and evolution of stars, galaxies, and clusters as well as the source(s) of the cosmic infrared background. The BLAST focal plane will consist of arrays of silicon nitride micromesh (?spider-web?) bolometric detectors operating at 300 mK coupled to 2 flambda feedhorn arrays. These arrays have been tested using the BOLOCAM instrument on the CSO and are identical to those that are being developed for the SPIRE instrument on the Herschel (formally FIRST) satellite. The first overnight test flight of BLAST will be in the autumn of 2002, and the first long duration balloon flight will be from McMurdo, Antarctica in 2003-2004.

M16. First Astronomical Use of Multiplexed Transition Edge Bolometers

D. J. Benford^a, J. A. Chervenak^a, E. N. Grossman^b, K. D. Irwin^b, S. A. Khan^c, B. Maffei^d, S. H. Moseley^a, F. Pajot^e, T. G. Phillips^f, C. D. Reintsema^b, C. Rioux^e, R. A. Shafer^a, J. G. Staguhn^a,g, C. Vastel^h
aNASA / GSFC, Greenbelt, MD
^bNIST, Boulder, CO
^cImperial College, London, UK
^dQMWC, London, UK
^eIAS, Paris, France
^fCaltech, Pasadena, CA
^gRaytheon/ITSS, Lanham, MD
^hCESR, Toulouse, France

We present performance results based on the first astronomical use of multiplexed superconducting bolometers. The Fabry-Perot Interferometer Bolometer Research Experiment (FIBRE) is a broadband submillimeter spectrometer that achieved first light in June 2001 at the Caltech Submillimeter Observatory (CSO). FIBRE's detectors are superconducting transition edge sensor (TES) bolometers read out by a SQUID multiplexer. The Fabry-Perot uses a low resolution grating to order sort the incoming light. A linear bolometer array consisting of 16 elements detects this dispersed light, capturing 5 orders simultaneously from one position on the sky. With tuning of the Fabry-Perot over one free spectral range, a spectrum covering Deltalambda/lambda=1/7 at a resolution of deltalambda/lambda~ 1/1200 can be acquired. This spectral resolution is sufficient to resolve doppler broadened line emission from external galaxies. FIBRE operates in the 350 µm and 450 µm bands. These bands cover line emission from the important PDR tracers neutral carbon [CI] and carbon monoxide (CO). We have verified that the multiplexed bolometers are photon noise limited even with the low power present in moderate resolution spectrometry.