Feasibility study of a single-device Phoswich detector for mixed-radiation monitoring: simulation-based evaluation of α/β/γ spectroscopy and practical applicability

Abstract Conventional surface contamination monitoring at radiation facilities and nuclear-medicine settings requires separate detectors for α-, β-, and γ-rays, complicating simultaneous measurement. A three-layer Phoswich scintillation detector (ZnS(Ag)/plastic/GSO(Ce)) enables single-device discrimination via pulse shape discrimination (PSD), but predicting its response is challenging due to complex optical transport and nonlinear energy loss in dead layers. We developed a Geant4 simulation model validated against SRIM (Stopping and Range of Ions in Matter) and ESTAR (Electron STopping powers And Ranges) stopping-power codes to evaluate radiation-type discrimination and nuclide identification feasibility. The simulated photomultiplier tube (PMT) photon-count distributions revealed substantial overlap between β-particles and γ-rays, demonstrating that PSD is essential. Provided that PSD-based classification is achieved (experimentally established for the present configuration), energy resolutions of 3.92–5.24% (α, 3.5–8.0 MeV) and 12.77–17.83% (β, 1.0–3.0 MeV) were obtained, sufficient for identifying α-emitter ( 211 At) and β-emitters ( 90 Sr– 90 Y, 137m Ba). γ-emitters ( 99m Tc, 111 In, 201 Tl, 18 F, 137 Cs) were identified via photopeaks, while higher-energy γ-rays produced Compton continua. L’Hoir asymmetric fitting extracted α and β peak centroids under area-source conditions. This study provides a quantitative foundation for single-device Phoswich detectors in mixed-radiation monitoring across radiation-facility and nuclear-medicine environments.