DELAYED THERMALIZATION OF X-RAYS ABSORBED IN TIN FILMS FAR BELOW THE SUPERCONDUCTING TRANSITION-TEMPERATURE

As part of a program for developing high resolution X-ray detectors, w e have deposited 4 mum thick Sn films on silicon calorimeters to serve as X ray absorbers. Thermistors in the silicon measured the temperatu re increase resulting from the thermalization of an X-ray photon. Silv er-filled epoxy was placed on the Sn to establish a complete thermaliz ation reference. The devices were operated near 0.1 K and below. Signa l pulses resulting from the absorption of 6 keV photons in the Ag epox y rose faster, peaked higher, and decayed to baseline more quickly tha n those resulting from absorption in the Sn. Taking the Ag pulse shape to be the impulse response of the detector, we deconvolved it from th e average Sn pulse shape to obtain the thermalization function in the Sn. The result contained a slow component with a thermalization rate o n the scale of several milliseconds. We consider this an indication of the quasiparticle recombination time in the Sn during the non-equilib rium condition following X-ray absorption. We were able to manipulate the thermalization by heating the device above the Sn transition tempe rature and varying the amount of magnetic field present upon cooling.