Scintillating fibre based beta spectrometer: Proof of concept by Monte-Carlo simulation and first experimental assessment

Abstract

We developed a new beta measurement method based on scintillating fibres, able to discriminate incident beta particles based on their energy, using various cladding thicknesses, which could find useful applications in the field of nuclear decommissioning and dismantling (D&D). Indeed, thanks to Monte Carlo simulations, we found that high-energy beta particles were less affected by thicker cladding than medium-energy beta particles. Therefore, combining different cladding thicknesses and a deconvolution method, we were able to identify and quantify convoluted beta spectra in a simulated scenario. In this paper, we describe the Monte Carlo simulations combined with the deconvolution algorithm based on the Maximum Likelihood-ExpectationMaximization method (ML-EM), and the associated experimental setup. We demonstrated the feasibility of such a method, using both simulated and experimental data, by deconvoluting 36Cl and 90Sr–90Y spectra, considering 36Cl as a medium-energy beta emitter and 90Sr-90Y as a high-energy beta emitter. Using fibres with only one thickness of cladding, we found that we could not estimate both contributions correctly, with errors reaching up to 71% of the actual activities. However, using two different acquisitions of fibres each one with a different cladding thickness, we were able to estimate both contributions with an error of 26% for 36Cl and 10% for 90Sr-90Y. Study of the improvement of these performances is presented and could help to fine-tune activities estimated. The next step of this work would consist in designing a beta spectrometer, based on scintillating fibres, and assess its performances. Taking advantage of both deformability capacity of scintillating fibres and their potential lengths up to a few metres, we expect that such a detection system will be well adapted to the radiological characterization of large surfaces, and suitable for deployment on uneven surfaces.