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

Abstract

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 3.4cm×3.4cm area has an imaging capability in the lower energy band for the HXI covering 5–80keV. The Si-pad consists of 16×16 pixels with a 5.4cm×5.4cm area and measures a photon direction with the Compton kinematics in 10–600keV. 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 150MeV 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−−1.1nA/cm2 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.