Thermal detection of X-rays

Small thermal calorimeters operating at temperatures near 100 mK are being developed for use on sounding rocket investigations of cosmic X-raysources. Similar detectors should be useful for high resolution laboratory spectroscopy of events in the tens of eV to tens of keV energy range. Unique features of this kind of detection include sensitivity to non-ionizing events and the capability of embedding the source to be studied within the detector. There appear to be fundamental limitations on the performance of cryogenic calorimeters based on doped semiconductor thermistors. Results on thermistor sensitivity and heat capacity, and preliminary data on excess noise that seem to be fundamental to the conduction process are presented. Both of these effects scale similarly and result in an optimum heat capacity of the thermistor for best energy resolution. (author) 7 refs.; 9 figs