Study of energy response of Gd2SiO5:Ce3+ scintillator for the ASTRO-E hard X-ray detector

The energy-dependent response of the crystalline oxide scintillator Gd₂SiO₅:Ce³⁺ (GSO:Ce) is studied in the energy range from 14 to 662 keV as a part of the preflight calibration of the hard X-ray detector (HXD) onboard the ASTRO-E satellite. In the relation between photon energy deposited and light yields, there exists nonproportionality and discontinuity around the energy of the gadolinium K-edge (50.2 keV). In 16 GSO scintillator units of the HXD flight model, the same characteristics of the energy response are confirmed. To evaluate the response across the K-edge quantitatively, we measure the “electron response” by means of the Compton coincidence technique. By using the electron response of the GSO crystal, we calculate the light yield nonproportionality as a function of deposited photon energy. We find that a photopeak line profile of the 59.5-keV emission of ²⁴¹Am is well modeled by a composite Gaussian. This will be discussed in terms of the light yield nonproportionality