The effect of large doses of radiation on of composite radiation-resistant scintillators cracking

In our previous works in this series, we investigated composite scintillators, i.e. scintillators based on a transparent gel composition containing single crystal grains of inorganic crystals (GSO:Ce, GPS:Ce, Al2O3:Ti, YSO:Ce and YAG:Ce). The gel composition was not only a binding material for scintillation grains. It was both a light-collecting medium in which a total scintillation signal from various grains was forming as well as a coating that protected scintillation grains from the effects of chemically active components of the atmosphere. At large cumulative doses of D, we observed a previously undescribed effect of scintillator cracking. In this work, as in previous works in this series, we irradiated composite scintillators on a linear electron accelerator. The electron energy was 10 MeV. We irradiated for a low (0.2 Mrad/h) and a high dose rate (1500 Mrad/h). At the low dose rate, cracking occurs at lower D values (about 100-200 Mrad) than under irradiation with the high dose rate (up to 500 Mrad). The luminescent characteristics of the scintillator changed insignificantly until the gel composition fixing single-crystal grains cracked. After the destruction of the gel composition, an abrupt deterioration in the properties of the sample was occurring. Additional studies have allowed us to show that nitrogen compounds, including nitric acid, can appear in the irradiation zone under the influence of radiation. The scintillator in the irradiation zone can either begin to expand under the influence of heating or (and) to crack when exposed to aggressive atmospheric components. There are two main hypotheses for describing the cracking of composite scintillators, requiring an analysis of the irradiation conditions, which this work is devoted. In this article, we conducted additional studies when the irradiated scintillators were in the atmosphere, or in a vacuum to compare and analyse the "temperature" and "radiation-chemical" hypothesis of composite scintillators cracking, as well as to confirm the conclusions of our analysis. The analysis we carried out in work proves that, at the low dose rate, nitrogen-containing compounds forming in the irradiation zone have a decisive influence on the effect of scintillator cracking. At the high dose rates, the main effect that leads to the cracking of scintillators is their heating, occurring under the influence of radiation.