In-situ estimation of gamma-ray source location at a specific depth based on a coded-aperture gamma camera

The coded-aperture gamma imager, EPSILON-G, was employed to swiftly identify gamma-ray sources in-situ. EPSILON-G is a device that gathers data using a detector module that integrates a GAGG(Ce) scintillator with a SiPM array and accurately locates gamma-ray sources through image reconstruction. To confirm its imaging capability and performance in-situ, the minimum count rate for imaging (MCI) was determined using MCNPX-PoliMi code simulations. Using the MCI, the minimum detectable activity (MDA) was calculated as representing the concentration at which surface radioactivity can be feasibly reconstructed in-situ. Additionally, a depth estimation method utilizing dual image acquisition was developed to identify radioactive materials at specific surface depths during radiological emergencies. This depth estimation method was theoretically proposed and validated through experiments with a 137 Cs gamma-ray source. The MDA satisfying the MCI for soil standards was 3.663 Bq/g. In-situ depth estimation experiments using a sandbox enabled the depth to be estimated up to 24.9 ± 2.3 cm with the 137 Cs (3.5 MBq) source.