Numerical Derivation of High-Resolution Detector Response Matrices for Airborne Gamma-Ray Spectrometry Systems

The objective of this work is to derive high-resolution spectral and angular detector response matrices of NaI(Tl) scintillation detectors for airborne gamma-ray spectrometry (AGRS) applications using a simulation-based numerical approach.The coupled gamma-ray and electron detector response was simulated using the high-fidelity multi-purpose Monte Carlo code FLUKA in an event-by-event mode and adopting high-performance computing. The simulation model incorporates a state-of-the-art non-proportional scintillation model. To validate the developed model, radiation measurements were conducted using calibration point sources with known activities and source-detector geometries under laboratory conditions.The detector response shows strong energy dispersion by various spectral features such as backscatter or annihilation peaks and also a pronounced sensitivity on scintillation non-proportionality effects. Furthermore, the simulations revealed a significant directional dependence of the detector response caused by the various hardware detector components and scintillation crystal geometry.These results show the importance for a detailed modelling of AGRS systems in a numerical calibration approach to prevent systematic errors in the simulated spectral and angular detector response. The general methodology presented herein can be adopted for numerical calibration as well as for spectral deconvolution of any inorganic-scintillator-based AGRS system.