Study of radiation damage to long BGO crystals

Abstract Results are presented on the decrease of the scintillation light output of long bismuth germanate (BGO) crystals at room temperature due to irradiation by 60 Co photons and 25 MeV electrons with doses from 50 to 5000 rad. After irradiation the light output recovers spontaneously. This recovery can be described by the sum of a minimum of three exponential functions. The shortest time constant is of the order of several hours, while the longest time constant is several hundred hours. The initial decrease in light output depends non-linearly on the dose applied and saturation effects have been observed. The damage induced by irradiation with 25 meV electrons is similar to the damage caused by 60 Co photons. The data are consistent with the view that only the absorption properties of BGO are changed by irradiation. For comparison, a NaI(Tl) crystal and a CsI(Tl) crystal have also been irradiated. Also, the effects on light transmission due to radiation damage to BGO are reported.