Radiation effects on the silicon semiconductor detectors for the ASTRO–H mission

Hard X-ray Imager (HXI) and Soft Gamma-ray Detector (SGD) onboard the 6th Japanese X-ray satellite, ASTRO–H, utilize double-sided silicon strip detectors (DSSD) and pixel array-type silicon sensors (Si-pad), respectively. The DSSD with a 3.4 cm×3.4 cm area has an imaging capability in the lower energy band for the HXI covering 5–80 keV. The Si-pad consists of 16×16 pixels with a 5.4 cm×5.4 cm area and measures a photon direction with the Compton kinematics in 10–600 keV. Since the ASTRO–H will be operated in a low earth orbit, these detectors will be damaged by irradiation of cosmic-ray protons mainly in the South Atlantic Anomaly. In order to evaluate damage effects of the sensors, we have carried out irradiation tests with 150 MeV proton beams and 60Co gamma-rays with a total dose of 10–20 years irradiation level. In both experiments, the leakage current has increased by ∼ 0.2 − − 1.1 nA / cm 2 under an expected operation temperature at −15 °C, which resulted in the noise level within a tolerance of 20 years. In this report, we present a summary of the basic performance of silicon detectors, and radiation effects on them by the irradiation tests.