Feasibility of a detector for nuclear radiation based on superconducting grains

We studied the sensitivity of a radiation detector based on metastable superconducting grains. Radiation is detected by the phase transition from the superconducting to the normal-conducting state of a grain induced by energy absorption. Metastable states of tin and cadmium grains were tested. The phase boundary of a large sample of grains was found to be broadened due to variations of the phase diagrams of single grains. Therefore, the use of superconductors with a low critical temperature T_c and an operation temperature close to T_c seems advisable to increase the sensitivity of the detector. For Cd grains a sensitivity normalized to the grain volume of 12 eV/μm ³ was achieved for the detection of γ rays. These grains showed an instability in the superconducting to normal-conducting phase transition for temperatures below 350 mK.