Radiation hardness and stability of optical coupling materials for BelleII electromagnetic calorimeter

Optical coupling materials are usually applied to ensure good optical matching in the APDscintillating crystal detection system. High transparency at the scintillating emission wavelength and material stability under irradiation are recommended requirements. In this work, silicon optical grease (BC630) and two-component epoxy resins (Epo-tek 301-2FL and Epo-tek 305), to be employed in electromagnetic calorimeter of the BelleII experiment at the Super-KEKB collider, were investigated to establish their radiation hardness and stability under gamma and neutron irradiation. Optical transmittance measurements were performed in the UV-VIS range, paying particular attention to the materials behavior in the range around 315 nm (CsI scintillating emission wavelength)