Solving the deep penetration problem in Monte Carlo simulation of airborne gamma-ray spectrum

Abstract Background: Monte Carlo (MC) simulation method is often used to estimate various parameters for analyzing gamma-ray spectrum, but the deep penetration constrains its application in airborne detection. Purpose: This study aims to find a solution for the deep penetration problem in MC simulation of airborne gamma-ray spectrum. Methods: When many of same-sized airborne gamma-ray spectrometry (AGS) are placed in the same height and the distances between the center of each AGS and the boundary of stratum are greater than the detectable radius, the response laws of these AGSs are the same under infinite source particles. Based on the principle, a spherical shell model of MC simulation for an airborne gamma-ray spectrum is proposed to solve the above problem. Results: Airborne gamma-ray spectrums of four calibration models are simulated by this spherical shell model on the MCNP (Monte Carlo N Particle) platform, which are in agreement with their respective observational average spectrums. Moreover, the estimated calibration factors of four radionuclides at 100-m altitude in the Vesivehmaa region of Finland are calculated by this method, which show an agreement within 20% error in comparison with the sampling methodology and simulation values of Allyson et al. Conclusion: The results verify that the spherical shell model has high simulation efficiency and can provide reliable parameters for inversing stratum information by airborne gamma-ray spectrum. (authors)