In-orbit activation study of ASTRO-H X-ray observatory using Geant4

We are developing an integrated simulation framework based on Geant4 to estimate in-orbit performance of instruments onboard ASTRO-H, the international X-ray observatory to be launched in 2014. One of the most important purposes of our simulation is to estimate radiation background of the Hard X-ray Imager (HXI) and the Soft Gamma-ray Detector (SGD), both of which are composed of CdTe and silicon. We developed a new code based on Geant4 to handle the generation and the decay of radioactive nuclei and to estimate the activation of CdTe detector. In addition, to verify simulation results, we performed beam irradiation experiments at NIRS IDMAC using 150 MeV protons, which is typical energy of protons reaching to the CdTe detectors placed in the shielding materials, and measured the activation background spectra for several months. Our simulation results show good agreements with the experimental data.