Effects of MeV Proton Irradiation on the Properties of Mo/Cu Bilayer Films

In the context of detector development for a proposed X-ray satellite mission, known as Hot Universe Baryon Surveyor (HUBS), we have studied stability in the properties of Mo/Cu bilayer superconducting films in a radiation environment. For this work, test devices were fabricated from the Mo/Cu films for four-terminal measurements. They were irradiated with 1MeV protons at room temperatures, with fluence ranging from 1.0 × 10^12 to 1.0 × 10^15 protons/cm ^2 . It was found that the superconducting transition temperature of the devices showed no systematic change with increasing irradiation fluence, but their residual resistance at low temperatures showed a decreasing trend when the fluence exceeded about 1.0 × 10^14 protons/cm ^2 . The former might be attributed mainly to defect migration and subsequent recombination at room temperatures, while the latter probably to the effects of annealing caused by heating of the bilayer material upon irradiation. Low-temperature irradiation experiments are required to reach firm conclusions. The results are compared with those of other investigations, and future plans are discussed.