A non-destructive, high-sensitivity, emergency dosimetry method using OSL from protective back-glasses from smartphones

Abstract

A non-destructive, high-sensitivity, dose-reconstruction method is proposed and tested using optically stimulated luminescence (OSL) from protective back-glasses from modern smartphones. A custom-made OSL reader, capable of accommodating the entire phone, has been built for this purpose and preliminary results are reported. The back-glass is stimulated using several light-emitting diodes (LEDs) while a radiation-induced OSL signal is detected with a high-sensitivity photomultiplier tube. A set of appropriate filters is used for separation of stimulation and emission light. The sensitivity of the system was tested for different wavelengths (colors) of stimulation light. A maximum sensitivity was observed using so-called Royal Blue LEDs, with stimulation centered at a wavelength of 447.5 nm. The following dosimetric properties have been studied: (1) background and radiation-induced OSL curves; (2) dose-response curves for several back-glasses from different phones and the corresponding values of the minimum detectable doses; and (3) fading of the OSL signal with time after irradiation. Background (BG) OSL signals were negligible in all tested phones except one (an iPhone 11), in which the BG signal was equivalent to a dose of ~157 mGy. However, the BG OSL had a different decay-curve shape compared to that of the radiation-induced signal (RIS). This difference in shape allows the two signals to be distinguished and separated. Strong, radiation-induced OSL signals were observed in all glasses after irradiation, but with significant variability in sensitivity among the different phones. The dose-response relationships for all phones were linear in the range 0–2.7 Gy when the OSL signals were measured at the same effective time after irradiation. Values of the minimum detectable doses were in the range 0.2–4.3 mGy for the different phones when measured 3 min after exposure. Fading of the OSL signal was observed for storage times up to 11 days after irradiation and was best-fitted by a power function. Dose recovery tests were carried out on two phones intentionally exposed to a dose of 266 mGy and their OSL measured 6 and 7 days, respectively, after irradiation. During these periods the phones were kept in their original cases but were used as usual for calls, messages, internet surfing, etc. Fading-corrected OSL doses were determined to be 199 mGy and 220 mGy, respectively, which are within 25% of the nominal value.