TITLE:
Gamma Spectrometry of Inhomogeneous Samples Using Peak-Ratio Method
AUTHORS:
Thomas M. Semkow, Liang T. Chu, Adam G. Burn
KEYWORDS:
Monte Carlo Simulation, Gamma Attenuation, Hot Particle, Effective Peak Efficiency, Signal Detection Theory
JOURNAL NAME:
Journal of Applied Mathematics and Physics,
Vol.9 No.11,
November
5,
2021
ABSTRACT: In gamma spectrometry of voluminous samples, inhomogeneous distribution of radioactivity caused by the presence of hot particles can create significant Bias in the results of activity determinations. We developed a novel method to reduce this Bias using the gamma-peak ratio. We show that the peak area ratio of two gamma peaks of different energies, emitted by the same radionuclide, is a sensitive measure of emitting source location and thus the inhomogeneity. A new calibration formula was then derived for true gamma efficiency pi as a function of efficiency ratio pi/pj of two peaks. This approach was verified by Monte Carlo simulations for a sample of 1-L volume containing from 1 up to 2048 of hot particles randomly distributed in a soil matrix. A 152Eu radionuclide was selected for calculations and we used various combinations of two gamma spectral peaks selected from three gamma energies of 121.8, 344.3, and 1408.0 keV. This new method is shown to reduce the Bias range and Bias standard deviation by several times when compared with the traditional homogeneous calibration applied to measuring hot particles. The method is independent of the number, location, and distribution of hot particles in the samples, and can be applied to a mixture of radionuclides. It complements our previous calibration model based on the peak-to-total ratio.