Radiation sensitive optical fibres for radiation detection and dosimetry

Abstract

Optical fibre-based alpha and beta particle sensing devices have been investigated for the purpose of detecting low levels of Uranium-238 and its decay products in liquids for mineral processing applications. Both sensors operate using the mechanism of scintillation produced within scintillating polymer optical fibres. The prototype devices which have been created are capable of performing direct, real-time, semi-continuous measurements of alpha and beta particle emitting radionuclides within solutions or suspensions, which is not possible with current measurement techniques. This work aims to help improve current processing techniques for the production of high quality copper concentrates from ore by monitoring the quantities and distributions of nontarget minerals throughout various mineral processing stages. Using the fibre fabrication facilities at IPAS, optical fibres have been drawn in-house from the commercial bulk scintillators EJ204 and EJ262 from ELJEN Technologies. Fibres with outer diameters of 160 μm were fabricated for alpha particle detection, and through refinement of the fabrication conditions, a transmission loss of 14 dB/m at 440 nm (EJ204) was achieved, down from > 30 dB/m in an earlier trial. 1 mm diameter canes were fabricated for beta particle detection, with transmission losses of 5 dB/m at 450 nm (EJ204), comparable to similar commercial fibre varieties. In-house fabricated fibres were tested alongside commercially available scintillating optical fibres in radiation sensing experiments, where their response to X-rays, alpha and beta particles were evaluated. Optical fibres have been tested under laboratory-simulated environmental conditions analogous to those encountered during mineral processing, where commercial fibres with outer claddings displayed the best performance. Prototype devices have been created and tested in real-world mineral processing solutions. Both alpha and beta particle sensors have demonstrated detection limits below the 1 Bq/ml per isotope of 238U target level. The work which has been presented shows the concept of using scintillating polymer fibres for low level radionuclide detection in liquids has been proven, and successful prototype alpha and beta particle sensors have been developed.