QUALITY ASSURANCE AND QUALITY CONTROL FOR THORON MEASUREMENT AT NIRS

摘要

The National Institute of Radiological Sciences (NIRS) has developed passive radon (~(222)Rn)-thoron (~(220)Rn) discriminative detectors for a large-scale survey and has established a thoron chamber to calibrate such detectors. In order to establish quality assurance and quality control for the ~(220)Rn measurement at NIRS, intercomparison studies have been carried out. The intercomparisons using a scintillation cell method, which has been used as a standard for ~(220)Rn measurement at MRS, were conducted at New York University (NYU, USA) and Physikalisch-Technische Bundesanstalt (PTB, Germany). As a result, it was found that the result from the NIRS was in good agreement with that from the NYU. On the other hand, it was observed that the relative discrepancy between the ~(220)Rn concentrations from the NIRS and PTB monitors was, on average, >50 %. Using the NIRS ~(220)Rn chamber, the international intercomparison experiment for passive ~(220)Rn detectors started in 2008.