Plastic scintillator beta ray scanner for in-situ discrimination of beta ray and gamma ray radioactivity in soil

Abstract

A beta ray scanner was proposed for in-situ discrimination of beta and gamma ray radioactivity. This scanner is based on the principle that gamma and beta rays experience different changes in detection efficiency in scintillators with different geometries, especially with regard to the scintillator thickness. The ratios of the counting rates of gamma rays (R-gamma), beta rays (R-beta), and sample measurements (R-total) in a thick scintillator to those in a thin one are reported. The parameter X-thick, which represents the counting rate contributed by beta rays to the total counting rate in the thick scintillator, was derived as a function of those ratios. The values of R-gamma and R-beta for Co-60 and Sr-90 sources were estimated as 3.2 +/- 0.057 and 0.99 +/- 0.0049, respectively. The estimated beta ray contributions had relative standard deviations of 2.05-4.96%. The estimated range of the beta rays emitted from Sr-90 was 19 mm as per the Monte Carlo N-Particle simulation, and this value was experimentally verified. Homogeneous and surface contaminations of Co-60 and Sr-90-Y-90 were simulated for application of the proposed method. The counting rate contributed by the beta rays was derived and found to be proportional to the concentration of Sr-90-Y-90 contamination. (C) 2019 Korean Nuclear Society, Published by Elsevier Korea LLC.