Experimental investigation of a heatless approach for initializing radiophotoluminescence glasses (FD-7) using ultraviolet light

Ag-doped phosphate radiophotoluminescence (RPL) glass dosimeter (RPLD) is widely used for radiation dosimetry. Although RPLD has the advantage of reusability through proper annealing, the current annealing process has undesirable features, such as heating at a high temperature (approximately 400 °C) and subsequent long (nearly half a day) cooling. In this study, we propose a new approach to initialize RPLDs more safely and rapidly using ultraviolet light (UV), which is expected to be preferable in many occasions, including quality assurance (QA) for radiotherapy. Four samples of commercially available RPLD glass (FD-7) with a size of φ1.5 mm × 12 mm were irradiated with X-rays (160 kV, 6.3 mA) at 0.1, 0.5, 1, 2, and 5 Gy (for H₂O) and exposed to UV from a high-pressure mercury UV lamp, which has a broad wavelength range with a dominant peak at 365 nm. RPL intensities were measured using an exclusive RPL readout system (FDG-1000, Asahi Techno Glass Co., Ltd.) at certain time intervals at room temperature. After 3-h UV exposure, the RPL intensity decreased by >90 % for irradiation of 1 Gy or higher, and 6-h UV exposure cleared >95 % of the RPL intensity for 2 Gy or higher. The RPL intensity increased slightly (2 % in 24 h at room temperature) after the termination of UV exposure. According to these findings, it is expected that the proposed heatless approach to initialize RPLDs, named ‘UV-annealing method’ here, will be effectively applied to routine dosimetry in relatively high-dose radiation fields, including radiotherapy facilities.