Characterization of radio-photo-luminescence (RPL) dosimeters under high dose X-ray irradiation

Abstract

Radio-Photo Luminescence (RPL) glasses are used as passive dosimeters, having a wide range of applications in different radiation fields, where low to high doses are absorbed. This work presents an experimental characterisation of FD-7, a commercial RPL glass dosimeter, irradiated with X-rays at different doses ranging from 0.3 kGy to 0.5 MGy. Investigation over such a broad range allows to enhance the understanding of RPL response in different dose level, out of their normal range of application up to 0.5 kGy. The purpose of this research is to achieve additional information on the response of FD-7 RPL glass dosimeters at high doses, to further their use in extreme high dose environment, especially targeting MGy range. The findings will be beneficial for the European Laboratory for Nuclear Research (CERN), where these dosimeters are used in environments in which such doses can be reached. In this study, a customized set-up has been developed, allowing the investigation of various relevant quantities, need to be measured in real-time. For instance, Radiation Induced Attenuation and transmittance response during irradiation and their recovery after irradiation are measured. It also allows to perform post-irradiation passive measurements. Parametric studies have been performed to assess the dependence of these quantities on the total absorbed dose and on the dose rate (ranging between 1.75 Gy/s and 0.175 Gy/s). Their kinetics during irradiation and recovery after irradiation are studied. Additionally, RPL signal evolution during irradiation with total absorbed dose up to 5 KGy at 1.036 Gy/s dose rate has been measured and reported, including settling of RPL signal to a constant intensity after irradiation. The RPL signal is normally used alone to determine the total absorbed dose, this technique being extensively used and considered as reliable up to approximately 0.3 kGy. For higher doses, a combination of both RPL signal and transmitted light is used to determine the total absorbed dose. Therefore, measurement of RPL signal in addition to transmitted signal measurement can provide a more complete view on the investigated phenomena at high doses. Finally, limitations of RPL dosimetry in certain dose ranges, especially within 0.3 kGy to 6 kGy, usually referred as mid-dose range are discussed based on the collected results and a novel method of combining RIA measurement with transmittance measurement is proposed in this thesis work to improve the accuracy and reliability of RPL dosimetry in this particular dose range.