Detector design study for online measurement of α and β total activity in drinking water

Abstract This paper proposes an innovative detector to measure the radioactivity of water based on ZnS(Ag)-coated plastic scintillating fibers. The system includes an internal cavity for measuring the total α and total β activities in the test water sample and an external cavity for excluding muons from external background radiation and reducing gamma rays in the internal water sample through anti-coincidence measurement. Geant4 simulations modeled radiation interaction, scintillation light generation, and its propagation within the detector. Simulation results are used to determine the optimal thickness of the ZnS(Ag) coating, length of the plastic scintillating fibers in the inner cavity, and thickness of the aluminum cylinder between the inner and outer cavities. When the ZnS(Ag) layer thickness is 14 μm, fiber length is 400 mm, and 353 fibers are arranged in parallel, the minimum detection limit for α particles is 0.5 Bq/L within 1.65 hours of detection time, and within 4.82 hours, the detection limit for β particles reaches 1 Bq/L.