Detection of Strontium-90, a Review and the Potential for Direct In Situ Detection

Strontium-90 is a by-product of nuclear fission and one of the primary beta emitting radionuclides found at nuclear decommissioning sites. Accidents, spills and leaks at nuclear waste facilities have dispersed strontium-90 into the environment, where it has mixed with groundwater. Given its radiotoxicity, activity levels must be carefully monitored to reduce the risk of exposure. Currently, monitoring is undertaken by sampling of groundwaters from boreholes and strontium-90 is radiochemically separated before its activity is counted. These procedures generate high quality results, but are time consuming, expensive and produce chemical waste. This paper reviews current techniques and proposes a novel approach through in situ beta detection, within groundwater monitoring boreholes, with gallium arsenide photodiodes. Gallium arsenide photodiodes are increasingly being applied to other forms of ionising radiation and have characteristics which make them suitable for rapid and mobile beta detection. To investigate this proposal, a 325 μm thick, proof of concept detector was modelled in the physics simulation software, Geant4. The simulation results indicate that the detector is physically capable of counting 99.31% of incident 0.4 MeV electrons, with 36.94% ± 0.04 % depositing all of their energy within the sensitive layer. This validation will provide the basis for further development of an in situ beta detector