Development of mobile scanning system for effective in-situ spatial prediction of radioactive contamination at decommissioning sites

摘要

In this study, a new mobile system was developed for in-situ scanning and prediction of spatial radiological contamination at nuclear decommissioning sites. The system analyses γ radioactivity, in addition to gross α and β activity, by scintillation spectrometry. Two Nal(Tl) scintillators are located at the centre of the γ-ray spectrometer and together function as a primary detector to track potential areas of elevated activity. Three polyvinyltoluene scintillators surround the primary detector, forming a guard detector to reduce background counts by suppressing Compton events. To validate the system, experimental and simulated γ-ray spectra were matched with respect to detection geometry and energy resolution. We analysed the performance of the system with surface soil under varying conditions, including homogeneity and vertical location of contamination and distance from the surface. Notably, we developed an effective quantitative method to predict the surface and vertical distributions of radioactivity in soil by correlation of detection efficiencies with peak-to-Compton ratios. Achievable scan minimum detectable concentrations for monitoring large areas were determined in case of moving the system. The results verify that the proposed system and prediction method are suitable for use at decommissioning sites and provide fair information for decision-making.