Beta detection of strontium-90 and the potential for direct in situ beta detection for nuclear decommissioning applications. Nuclear Instruments and Methods in

This paper examines the feasibility of detecting strontium 90 in groundwater directly with photodiodes and considers the physical parameters which maximise radiation absorption within the detector. Geant4 simulations were used to draw comparisons between silicon, gallium arsenide and cadmium telluride detectors of varying surface area and thickness. Detectors were compared in their ability to absorb point and scattered sources of radiation. The results indicate that a detector, of 10 mm 2 surface area, and 1 mm thickness offered the highest detection efficiency in a contaminated groundwater simulation. 1 mm thick and 100 mm 2 detectors cadmium telluride and gallium arsenide detectors were modelled in a groundwater borehole scenario. Each material offered similar detection efficiency, but the greater backscattering effect in cadmium telluride resulted in a greater peak at lower energies compared to that observed in gallium arsenide. K: Detector design and construction technologies and materials; Detector modelling and simulations I (interaction of radiation with matter, interaction of photons with matter, interaction of hadrons with matter, etc); Interaction of radiation with matter; Solid state detectors 1Corresponding author.

Strontium-90 is one of the primary beta-emitting radionuclides found at nuclear decommissioning sites. Monitoring its activity in the environment is of utmost importance given its radiotoxicity. Current procedures for the beta detection of strontium-90 are time consuming, produce secondary waste and expensive. There is a demand for real-time in situ radiostrontium monitoring in groundwater at nuclear decommissioning sites. This paper presents a review of existing techniques for strontium-90 monitoring and examines a novel approach through direct beta detection with a gallium arsenide photodiode based detector. A proof of concept detector was modelled in the physics simulation software, Geant4, and evaluated as candidate for in situ detection of beta emitting radionuclides. The simulation results indicate that the detector is physically capable of counting 89.86% of incident 0.546 MeV electrons from a 1 mm range in water. This validation will provide the basis for further development of an in situ beta detector.

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Strontium-90, as one of the primary beta emitting radionuclides produced during nuclear fission, strontium-90 contaminates groundwater at nuclear decommissioning sites after leaks and spills. Its presence in the groundwater presents a long-term site risk, and its activity must be routinely monitored. Existing techniques see groundwater samples collected from deep underground boreholes and sent to remote labs for analysis [1]. These procedures are expensive, time consuming and produce chemical waste, whereby eliminating the need for sample collection and treatment, the net lifetime monitoring costs of strontium 90 can be reduced [2]. In this paper authors present an optimisation of a beta detector, based on submersible photodetector, which can be used in real-time, in-situ beta detection. In order to directly detect and characterise strontium 90 in groundwater, it is essential to maximise the number of beta particles incident on the photodiode surface and ensure that they are fully absorbed within the sensitive region of the detector. This work has developed a Geant4 software framework for investigating the energy deposition by beta particles on photodiode detectors. A series of simulations have been performed to investigate radiation absorption in silicon, cadmium telluride and gallium arsenide detectors. Variations in sensitive area and detector thickness were modeled to determine their suitability for strontium-90 detection in groundwater. The optimal detector geometry of gallium arsenide photodiodes was further investigated. The simulation results and analysis suggest that the optimal detector will feature a large surface area, at least 1 cm2, and an intrinsic layer approximately 400 m thick.