DEVELOPMENT OF MEASUREMENT TECHNOLOGY FOR BETA-RAY DEPTH DISTRIBUTION IN SOIL

Abstract

Beta distribution measurement technology on the depth of soil was developed aiming for monitoring ofradioactive contamination in the site of decommissioned nuclear power plant. Two types of scintillators (CdWO4& BC-400; Saint-Gobain Crystals) were used for it. CdWO4 was more sensitive to gamma-ray than BC-400 while beta-ray sensitivity for both scintillators were similar. Gamma-ray contribution was estimated and eliminated from measured spectra by using this characteristic. Gamma-ray sensitivity ratio between CdWO4 and BC-400 was 5.433 in average depending on energy (5.91 to 5.30 from 511 keV to 1,330 keV) while beta-ray sensitivity ratio for 90Sr source was 1.023±0.002. Pure beta-ray source (only 90Sr) and combined source (90Sr and 60Co) was prepared with depth distribution. Relative errors between the measured count rate for pure beta-ray source and calculated count rate for combined source were varied from 2.55% to 20.9%.