Estimation of elapsed time after an unnoticed radiation exposure using the weathering resistant radiophotoluminescence glass (SAPANS)

Abstract

A method using a newly developed radiophotoluminescence (RPL) glass for estimating the elapsed time after an unnoticed radiation exposure was proposed and tested. Cuboid-shaped samples of a silver-activated glass composed of P2O5–Al2O3–Na2O–Ag2O, named “SAPANS”, were irradiated with 137Cs-source γ-rays at five dose levels (1.0, 2.0, 3.5, 5.5 and 8.5 Gy) and the time changes of the RPL intensities emitted from the samples stimulated by the UV pulses were observed for up to 97 days after irradiation. It was found that the RPL intensities continuously increased with the same build-up patterns keeping linear dose responses at all dose levels, and reached to about 86% of those after preheating at 160 °C for 1 h at 97 days after irradiation. According to this finding, it was proposed to use the SAPANS for estimation of the elapsed time after an accidental high-dose exposure as well as for the determination of radiation doses. The practicality of this approach was examined in a blinded experiment wherein five sets of the SAPANS samples were irradiated with unknown γ-ray doses at unknown timings in the period of 53 days. As results, the errors of estimated elapsed times were −25% for 4.5 h, 18% for 3.3 days, 70% for 10 days, 30% for 30 days and 0% for 45 days after irradiation. These findings indicate that the proposed method could be applied to retrospective dose assessment even when a few months have passed after an unnoticed radiation exposure.