A tungsten superconducting phase transition thermometer on a 32 g sapphire crystal has given an energy resolution of 100 eV (FWHM) for 1.5 keV X-rays, increasing to 440 eV at 14 keV. A possibility to obtain similar resolution in much larger crystals by using Al films as phonon collectors is presented.

Massive cryogenic particle detectors are being developed for use in a search for dark matter particles. Results with a 31 g sapphire crystal and a superconducting phase transition thermometer operated at 44 mK are presented. The observed signal includes a fast component which is significantly larger than the expected thermal pulse. The energy resolution is 210eV (FWHM) for 6keV X-rays.

We have studied the proximity effect in bilayers of thin films of iridium covered by gold. By varying the thicknesses of the iridium and gold layers, we achieved critical temperatures as low as 33 mK. The critical temperature of the bilayers is lower than predicted by the theory of de Gennes-Werthamer [J. J. Hauser, H. C. Treuerer, and N. R. Werthamer, Phys. Rev. 136, A637 (1964)], but adding a free parameter to the theory allows good agreement. The transitions of the bilayers typically had widths of a few mK, with the narrowest reaching 0.2 mK, and were always steeper than those of pure iridium films evaporated simultaneously. Such bilayers can be used as superconducting phase transition thermometers in cryogenic particle detectors.

We report on a calorimetric particle detector consisting of an 18.3 g silicon crystal and an iridium superconducting phase transition thermometer. The cryogenic calorimeter and the associated apparatus are described in detail. The pulses from irradiation with an α-particle source have a large unexpected overshoot in addition to the component expected from a naive thermal model. The pulse height spectrum displays an energy resolution of 1% FWHM at 6 MeV and good linearity. The noise, electrothermal feedback, and position dependence are discussed.

At the Technische Universität München and MPI München, we are studying calorimetric particle detectors utilizing absorber crystals and super-conducting transition edge thermometry. High resolution results from the low absorber heat capacity and the strong temperature dependance of the resistance of the thermometer at the superconducting — normal phase transition. The thermometer signals are monitored with a SQUID, and subsequent pulse height analysis is performed. Detector performance is discussed relative to SQUID characteristics, and SQUID system slew rate limitations are specifically addressed. Prototype detector results are presented.

To improve the sensitivity of calorimetric particle detectors we want to produce low-Tc superconducting thin films to be used as phase transition thermometers. We have succeeded in depositing epitaxial α-tungsten films on sapphire which have critical temperatures Tc near 15 mK. To our knowledge this is the first time that the Tc of bulk tungsten has been observed in thin films. Such a film has been produced on a 4 g sapphire crystal and operated as a calorimeter, giving an energy resolution of 75 eV (FWHM) for 1.5 keV X-rays.

We have studied the proximity effect in bilayers of thin films of iridium covered by gold. These structures were evaporated onto sapphire single crystals for use as phase transition thermometers in cryogenic particle detectors. By varying the thicknesses of the iridium and gold layers, we achieved critical temperatures as low as 33 mK. The critical temperature of the bilayers is lower than predicted by the theory of de Gennes-Werthamer, but adding a free parameter to the theory allows good agreement. The transitions of the bilayers typically had widths of a few mK, with the narrowest reaching 0.2 mK, and were always sharper than those of pure iridium films evaporated simultaneously.

We plan a dark matter search using cryogenic calorimetric detectors with superconducting phase transition thermometers. We discuss such an experiment, compare its estimated sensitivity range with other dark matter searches, and discuss its planned realization.

We present results obtained with detectors consisting of dielectric absorber crystals and super-conducting phase transition thermometers made of Ir/Au bilayers. With a 31 g sapphire crystal and an Ir/Au thermometer operated at 45 mK we have obtained an energy resolution of 220 eV (FWHM) for collimated 5.9 keV X-rays. To explain the measured pulse shapes we have developed a model which includes the effect of non-thermal phonons. Results obtained previously with a 18 g Si absorber and an Ir/Au thermometer with broad transition allowed checking this model over a wide temperature range. A heater experiment performed with this calorimeter provides further support of our model.

The author discusses the development of calorimetric detectors utilizing large absorber crystals coupled to superconducting transition edge thermometers. At low temperature, high energy resolution results from the low detector heat capacity and the strong temperature dependence of the resistance of the thermometer at the normal/superconducting phase transition. The transition edge thermometer is a thin film at very low T/sub c/ superconductor deposited directly on the absorber. Results from two detectors yielding excellent energy resolution are presented. One of these detectors was fabricated with an Ir strip thermometer, and the other with an Ir/Au proximity effect bilayer. Detailed studies have resulted in a model which will be used to optimize future detectors.< >