Quality control for Analysis of anthropogenic radioactivity at MRI

Monitoring of 90Sr, 137Cs and 239,240Pu in the atmospheric deposition samples has been continued for longer than 40 years at the Meteorological Research Institute, Japan (MRI). Our company (KANSO) has been in charge of the analyses of these radionuclides as a contractor for the recent several years. It is basic requirements to produce good quality data for the contractor in the long-term monitoring; each technician engaged in the analyses should not have the skill difference. Furthermore, the data produced should not involve any bias and whatever problems. We have, therefore, carried out the analytical quality control and assurance QC/QA) by using the MRI reference fallout material for radioactivity along with analysis of the real samples. In the present work, those results of the QC/QA at the MRI by the KANSO are presented. For the analyses of 90Sr (n=65) and 137Cs (n=158), good quality control has been achieved; the coefficient of variations were fairly small, less than 5%. Also, the deviation from the reference values for these two nuclides were within 2%. While for the analysis of 239,240Pu (n=40), the coefficient of variation was worse, almost 10%. The deviation from the reference values for Pu isotopes were worse, about 10%, as well. From the normalized frequency distribution for the data, it was shown that 90Sr and 137Cs have good normal distributions. While the 239,240Pu data showed slightly disturbed frequency distribution. This difference does not seem attributable to the skill level of the technicians engaged but the inhomogeneity of the 239,240Pu in the reference fallout material itself. The control plots were depicted to see if any low quality data. From this time series data analysis, few deviated data were found. The deviated data were not attributable for the replace of the technicians and equipments but probability reason. As a whole, good QC/QA was practically achieved in the analyses of 90Sr, 137Cs and 239,240Pu in the atmospheric deposition samples by the contractor, KANSO, at the MRI, Japan. (author)