Date of Award
Doctor of Philosophy
School of Science
Associate Professor Steven Hinckley
Dr Graham Wild
Field of Research Code
This study investigates the use of Optical Fibre Bragg Grating Sensors (FBGs) for Gamma Radiation Dosimetry. A comparative analysis of responses to gamma irradiation between standard commercial FBGs and new generation FBGs written in Photonic Crystal fibre (PCF) were examined under similar regimes and conditions. Current research suggests that the FBGs performance, when exposed to Cobalt-60 gamma irradiation, can suffer cross sensitivity problems resulting from different external effects such as temperature. However, FBGs written in PCFs may be able to overcome these problems due to their design, flexibility of the shape, and size of the micro-holes in a PCF.
Previous research has indicated the Bragg wavelength shift (BWS) of standard FBGs increases with accumulated Gamma dose. This shift appears to be permanent, indicating that gamma irradiation permanently affects the Bragg wavelength of the FBG. To better understand these effects, and determine the suitability of particular FBGs for use in radiation dosimetry, measurements in relation to the effects of pre-irradiation, dose rates and accumulated dose, and relaxation effects were performed on both sets of FBGs. To simulate real time conditions of a radiation dosimeter, the FBGs are examined through three consecutive radiation stages followed by limited recovery times. There is a lack of research in the areas of small recovery times and multiple periods of irradiation. The experimental regime and setup consisting of the three stages with very limited recovery comparing PCF-FBGs and standard FBGs (STD-FBGs) is unique. The experiments and gamma irradiation were conducted at ANSTO (Australian Nuclear Science and Technology Organisation) using the GATRI (Gamma Technology Research Irradiator) irradiation facility. The responses after exposure to gamma irradiation, including relaxation periods between commercially manufactured FBGs written in Germanium (Ge) doped optical fibres, with and without hydrogen loading, along with the standard SMF-28 fibre with Hydrogen are shown. The FBG inscription in PCF was completed at Interdisciplinary Photonics Laboratories (iPL), University of Sydney. The FBGs in each fibre are written by Ultraviolet (UV) low energy irradiation. In nuclear environments, when FBGs have been exposed to gamma irradiation, changes in the Bragg wavelength occur, although the exact cause or trigger is still unclear.
The main outcome of this research has indicated that PCF-FBGs, compared to standard FBGs, are a strong candidate for use in the field of radiation dosimetry. This is due to their very consistent behaviour and recovery aspects after irradiation exposure. This work will compliment established research and help in the absolute quantitative comparison between the individual standard FBGs and PCF-FBGs. It will help in establishing FBGs as a possible replacement to present physical and chemical sensors currently being used as radiation dosimeters.
Baccini, D. (2019). Gamma irradiation response of photonic crystal and standard optical fibre Bragg grating sensors for radiation dosimetry. https://ro.ecu.edu.au/theses/2226