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 A STRO-E satellite. In the relation between photon energy deposited and light yields, there exists nonproportionality and discontinuity around the energ y 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 confi rmed. 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 yiel d nonproportionality as a function of deposited photon energy. We find that a photopeak line profile of the 59.5-keV emission of Am-241 is well modele d by a composite Gaussian. This will be discussed in terms of the light yie ld nonproportionality.