Annealing of proton radiation damages in Si-PM at room temperature

We report the radiation damage results of two new types of Multi-Pixel Photon Counter (MPPC) under the 200 MeV proton beam, for cosmic gamma-ray observations with CubeSats. The new MPPCs, S13360-6050CS and S14160-6050HS, have recently become commercially available by Hamamatsu Photonics K.K. (HPK). After 100 rad irradiation, the dark current increased by a factor of ∼100 and the threshold energy of gamma-ray detection by CsI scintillator increased, but S14160-6050HS was less degraded. We then confirmed the annealing effects of the dark current and threshold energy for both. The decrease rate of the dark current in both MPPCs were similar to those in the previous works. At 20 °C, the threshold energies of both MPPCs reduced by several tens of percent after irradiation, but below 0 °C, the threshold energy of S14160-6050HS was not significantly lowered. We also confirmed that annealing began before one month post-irradiation.