THERMALIZATION OF X-RAYS IN EVAPORATED TIN AND BISMUTH-FILMS USED AS THE ABSORBING MATERIALS IN X-RAY CALORIMETERS

We have investigated the use of evaporated tin and bismuth films as th e absorbing materials in X-ray calorimeters. When the films were depos ited directly on monolithic silicon calorimeters, the output signal fr om both Sn and Bi devices was strongly dependent on the location of th e absorption event relative to the ion-implanted thermistors, presumab ly indicating thermistor sensitivity to a non-thermal spectrum of phon ons. With Sn films we also observed that a component of the thermaliza tion proceeded slowly, relative to a complete thermalization reference . The thermalization function could be modified by trapping magnetic f lux within the film. In order to distinguish thermalization effects in the films from the thermistor sensitivity to energetic phonons, we de posited Sn and Bi films on thin Si substrates which we then affixed to calorimeters using epoxy. With glued Sn films, we were able to attain as good as 13.6 eV resolution of 6 keV X-rays with no excess broadeni ng of the line beyond the width of the baseline, while similarly made Bi devices showed excess broadening.