Ge-doped silica fibre for proton beam dosimetry

An investigation has been made of nominal 2.3 mol% and 6.0 mol% germanium (Ge) doped cylindrical optical fibres as novel radiation dosimeters for 150-MeV proton beam measurements. These optical fibres were locally fabricated using a modified chemical vapour deposition technique with a subsequent pulling process. Combined scanning electron microscope and energy dispersive X-ray spectroscopy analyses were performed to map the relative presence of the germanium and other elements in the optical fibres. Prior to irradiation, a thermal annealing process was carried out to erase any pre-irradiation signals potentially existing in the samples. Results were compared against nanoDot™, TLD-100, and commercial optical fibres to allow for a relative comparison of the response. For radiation dose in the range 1 up to 10 Gy, the fabricated optical fibres exhibit excellent radiation dose response (R2 > 0.99), with a linearity index that remains close to one (indicating a linear response). In terms of minimum detectable dose, these optical fibres are able to detect relatively low radiation dose (for the present batch of fibres down to 10.7 mGy). After repeated various irradiation campaigns, the fabricated optical fibres have been shown to provide consistent response, effectively without noticeable change in thermoluminescence (TL) yield (ANOVA, p > 0.05), suggesting excellent reproducibility. In regard to signal fading, 96 days post-irradiation the fabricated optical fibres showed minimal signal loss, at 19% at the most. These dosimetric characteristics confirm the potential of the fabricated optical fibres as TL dosimeters, specifically for present studies in conducting proton beam measurements.