Effect of gamma-induced defects on the activator glow in Lu-=SUB=-2-=/SUB=-SiO-=SUB=-5-=/SUB=- : Ce scintillator crystals

Abstract

Correlations were studied between the optical absorption (OA) spectra and the integral curves of thermal glow (TG) in 300-600 K after irradiation of Lu2SiO5 : Ce scintillation crystals with 60Co gamma-quanta (1.17 and 1.33 MeV) at the dose rate 1.1 Gy/s in the dose range 70-5·107 Gy at 310 K and their gamma-luminescence (GL). There are intrinsic defects caused by technological process, such as neutral VO5-centers with OA band at 193 nm and charged =Si-VO5 --- 213 nm, Lu1-F^+-Si --- 238 nm, Ce3+/Ce4+ --- 263 nm, and Ce3+/F --- 295 nm centers. Irradiation to the dose 5·104 Gy resulted in decreasing in VO5-center concentration, but did not influenced on others. While, after doses >5·104 Gy concentrations of all other mentioned defects grew. The observed recovery of OA at 193 nm and decrease in TG peak at 335 K with the ageing time (1, 3 and 10 hours) at 305 K, and also the correlated growth of OA at 238 nm and TG peak at 540 K after serial irradiations to doses from 70 to 2.3·106 Gy are due to releasing electrons from these color centers followed by radiative recombination at Ce1-centers. However Ce3+ GL yield decrease at 400 and 420 nm at doses >105 Gy is possible related with increasing concentrations of =Si-VO4, Lu1-F^+-Si and Ce3+/F centers, which compete with Ce1 ones in trapping electrons. Thus, the upper limit for stable Lu2SiO5 : Ce gamma-scintillation is 105 Gy. Keywords: Lu2SiO5 : Ce, color centers, gamma-induced luminescence, scintillation dose limit.