Thickness dependent sensitivity of GAGG:Ce scintillation detectors for thermal neutrons: GEANT4 simulations and experimental measurements

In the present work, we report extensive GEANT4 simulations in order to study the dependence of sensitivity of Gd₃Ga₃Al₂O₁₂:Ce (GAGG:Ce) scintillation crystal based detector on thickness of the crystal. All the simulations are made considering a thermalised Am-Be neutron source. The simulations are validated, qualitatively and quantitatively, by comparing the simulated energy spectra and sensitivity values with those obtained from experimental measurements carried out using two different thicknesses of the crystal from our own experiment (0.5 mm and 3 mm) and validated with three other thicknesses (0.01 mm, 0.1 mm and 1 mm) from literature (Taggart et al. in IEEE Trans Nucl Sci 67:603–608, 2020). In this study, we define sensitivity of GAGG:Ce as the ratio of area under 77 keV sum peak to 45 keV peak. The present studies clearly confirm that, while it requires about 0.1 mm thickness for the GAGG:Ce crystal to fully absorb thermal neutrons, it requires about 3 mm to fully absorb the thermal neutron induced events. Further, we propose an equation, that can be used to estimate the thickness of the GAGG:Ce crystal directly from the observed sensitivity of the GAGG:Ce crystal. This equation could be very useful for the neutron imaging community for medical and space applications, as well as for manufactures of cameras meant for nuclear security purposes.