Comprehensive experimental validation of Monte Carlo model for imaging plate response to ^198gAu and interference from...

The gold activation method, based on the determination of ^198gAu radioactivity produced via the ¹⁹⁷Au (n,γ)^198gAu reaction, is widely used for thermal neutron fluence rate measurements in accelerator facilities. Since the early 2000s, imaging plates (IPs) have been employed to visualize the spatial distribution of induced radioactivity by detecting β and γ rays from activated foils. However, in high-energy accelerator environments, the interfering activity of ^196gAu can affect the detection of ^198gAu, the principal activation product for thermal neutron assessment. In this study, the response of a Fujifilm BAS-MS IP to the decay radiations of ^198gAu and ^196gAu was quantitatively evaluated by establishing a Monte Carlo simulation model using the Particle and Heavy Ion Transport code System (PHITS) and conducting comprehensive experiments using activated gold foils with different radionuclide compositions to validate the model. The simulation incorporated the transport of decay electrons and photons, the depth-dependent energy deposition in the photostimulable phosphor layer, and the escape probability of PSL photons. The results showed that β rays from ^198gAu dominate the PSL signal formation in the shallow regions of the phosphor layer, producing roughly five times higher sensitivity than ^196gAu. As the gold foil thickness increases, self-absorption of β rays significantly reduces the PSL detection efficiency. A comprehensive evaluation revealed that a foil thickness of 20-30 μm provides an optimal balance between sensitivity and self-absorption. These findings establish a validated Monte Carlo model for quantitative PSL response analysis and provide practical guidance for optimizing activation-foil-based thermal neutron measurements in accelerator facilities.