Geant4 Monte Carlo radioxenon beta-gamma coincidence efficiency simulation for a phoswich detector

In this work, a Monte Carlo (MC) simulation model is established to accurately characterize a phoswich beta-gamma coincidence detector system. This model can be easily used to predict the beta-gamma coincidence efficiencies of xenon radioisotopes at various stable xenon concentrations in the counting cell. The results demonstrate that there is a significant inverse correlation between beta-gamma coincidence efficiency and stable xenon concentration. The influence of stable xenon concentration on beta-gamma coincidence counting efficiency has been investigated for each individual xenon radioisotope. The results indicate that the effect of stable xenon concentration on beta-gamma coincidence efficiency depends on the xenon radioisotope and its decay modes. The coincidence efficiency of (133)Xe with 31.0-keV X-ray decay mode is the most affected one; and then followed by (131m)Xe, (133)Xe with 81.0-keV gamma-ray decay mode, (133m)Xe and finally (135)Xe. The study also indicates that the gamma absorption by xenon gas plays more of a role in the decrease of beta-gamma coincidence efficiency for (133)Xe and (135)Xe, and that the conversion electron spectrum shifting and broadening plays more of a role in the reduction of beta-gamma coincidence efficiency for the metastable radioxenon of (131m)Xe and (133m)Xe.