Development of Measurement Technology for Beta-Ray Depth Distribituion in Soil

Abstract

Beta distribution measurement technology on the depth of soil was developed aiming for monitoring of radioactive 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%.