The impact of proton induced radioactivity on the LSO:Ce, YSO:Ce scintillation detectors

Scintillation materials based on of RE₂SiO₅:Ce (RE=Gd, Lu and Y) single crystals are widely used for the detection of low energy γ-rays in medical imaging devices and other safety systems. Such oxy-orthosilicate crystals can be manufactured by Czochralski method by many producers, which have large production capacities. Recently it has been proposed to use these types of materials for high energy physics experiments. However, the operational conditions at high luminosity experiments foreseen for the High Luminosity LHC at CERN impose stringent requirements on the detector materials in terms of radiation hardness in order to ensure a reliable data taking over its lifetime. As a consequence, detailed radiation hardness studies have to be carried out on detector modules in order to provide reliable estimations of the degradation of the detector performance, in particular under hadron irradiations. Recently we reported on the radiation damage effects in RE₂SiO₅:Ce (RE= Lu, Y) crystals under gamma and proton irradiation. Both type of crystals have shown a minor change of the optical transmission both under γ-rays and 24 GeV proton irradiation in the wavelength region of scintillation. However, we showed that lutetium oxy-orthosilicate (LSO) shows strong phosphorescence after irradiation with high energy protons, whereas yttrium oxy-orthosilicate (YSO) does not show it. Such phosphorescence is due to induced defects and metastable color centers. In addition, long-lived phosphorescence can also be due to an induced radioactivity in the material itself and mechanical support material of detector modules as well. In this work we compare the impact of induced radioactivity on the properties of Lu₂SiO₅:Ce and of Y₂SiO₅:Ce detector modules of different configurations including homogeneous and “shashlik” type.