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

摘要

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 (Rgamma), beta rays (Rbeta), and sample measurements (Rtotal) in a thick scintillator to those in a thin one are reported. The parameterXthick, 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 ofRgammaandRbetafor60Co and90Sr 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 from90Sr was 19?mm as per the Monte Carlo N-Particle simulation, and this value was experimentally verified. Homogeneous and surface contaminations of60Co and90Sr-90Y 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 of90Sr-90Y contamination.