Validation of a High-Fidelity Monte Carlo Model for Airborne Gamma-Ray Spectrometry with Field Measurements

The objective of the present study is to simulate the spectral gamma-ray response of the Swiss Airborne Gamma-Ray Spectrometry system (SAGRS) using Monte Carlo radiation transport codes. The SAGRS is mounted in the cargo bay of a AS-332M1 Super Puma helicopter from the Swiss Air Force and consists of four prismatic NaI(Tl) scintillation crystals with a total volume of 16.8 l. We developed a high-fidelity Monte Carlo model of the SAGRS including the detector system and the helicopter using the multi-purpose radiation transport code FLUKA. As part of the measurement campaign ARM22c organized by the National Emergency Operations Centre (NEOC), we performed hover and line flights in combination with ground measurements using certified 133Ba and 137Cs point sources to validate our model. The performed measurements revealed a significant impact of the helicopter fuel on the detector response for various solid angles. In general, we found an excellent agreement between the measured and simulated detector response with relative errors in the full energy peak <10%. The validated model presented herein offers a novel way to simulate the spectral detector response of the SAGRS for the generation of fundamental spectra in a full spectrum analysis framework.