Irradiation Tests of Silicon Photomultipliers for Use in Space

For using silicon photomultipliers (SiPMs) in space experiments, we conducted irradiation experiments of SiPMs with protons and iron ions. In particular, the relationship between leakage current and radiation dose was investigated under various irradiation conditions to determine techniques of mitigating damage caused by radiation. The leakage current was approximately proportional to dose; however, the proportionality constant did not significantly vary with irradiation conditions. The effects of annealing after irradiation tests indicated no substantial decrease in leakage current. Conversely, while the leakage current increased with dose, the SiPMs continued to operate even after 5 krad of irradiation, which corresponds to several years of radiation exposure in space at altitudes of ~400–500 km. The results obtained from these irradiation tests are used to characterize a hard X-ray (>60 keV) detector for space-based applications. This detector couples an inorganic scintillator with a high light yield, such as CsI(Tl), to an SiPM.