MODEL FOR CRYOGENIC PARTICLE DETECTORS WITH SUPERCONDUCTING PHASE-TRANSITION THERMOMETERS

We present data on a detector composed of an 18 g Si crystal and a sup er-conducting phase transition thermometer which could be operated ove r a wide temperature range. An energy resolution of 1 keV (FWHM) has b een obtained for 60 keV photons. The signals consist of two components : a fast one and a slow one, with decay times of 1.5 ms and 30-60 ms, respectively. In this paper we present a simple model which takes ther mal and non-thermal phonon processes into account and provides a descr iption of the observed temperature dependence of the pulse shape. The fast component, which completely dominates the signal at low temperatu res, is due to high-frequency non-thermal phonons being absorbed in th e thermometer. Thermalization of these phonons then leads to a tempera ture rise of the absorber, which causes the slow thermal component. At the highest operating temperatures (T similar to 80 mK) the amplitude of the slow component is roughly as expected from the heat capacity o f the absorber. The strong suppression of the slow component at low te mperatures is explained mostly as a consequence of the weak thermal co upling between electrons and phonons in the thermometer at low tempera tures.