Radionuclide activity measurements in environmental samples of water, soil and grass: CCRI(II)-S4 comparison report

Abstract

In the frame of the Mutual Recognition Arrangement of the International Committee for Weights and Measures, the Consultative Committee for Ionizing Radiation Section II—Measurement of Radionuclides—proposed to the national metrology institutes of Member States signatories of the Metre Convention, to participate in an interlaboratory comparison exercise on the determination of gamma emitting radionuclides in soil, grass and water. The exercise was piloted by the Reference Materials Group at the IAEA's Laboratories in Seibersdorf (Austria).The exercise is classed as a supplementary comparison, with reference CCRI(II)-S4 and the present report will be referenced in the Bureau International des Poids et Mesures (BIPM) key comparison database (KCDB).Five national metrology institutes took part in the present interlaboratory comparison exercise: the Czech Metrology Institute, the National Centre of Metrology, Bulgaria, National Institute of Standards and Technology, USA, the National Physical Laboratory, UK, and Physikalisch-Technische Bundesanstalt, Germany. In addition, two expert laboratories participated in this comparison: the Japan Chemical Analysis Centre, Japan, and the IAEA Chemistry Unit of the Physics, Chemistry and Instrumentation Laboratory in Seibersdorf, Austria.This comparison was aimed at: supporting calibration and measurement capability (CMC) claims of national metrology institutes for radionuclide measurements in different matrices (grass, soil and water), and assigning the certified reference value of the 372 grass Certified Reference Material.This report presents the sample preparation methodology, participants' results and data comparison approach.Appendix I contains the analytical results sorted according to the analyte with the Mixture Models Median (MM-median) graphs. Appendix II reports tables of results evaluation, including uncertainty budgets sorted by institute. Appendix III contains the documentation used in this comparison. The comparison study materials were prepared and distributed to the participating laboratories in June 2006. The deadline for receiving the results from the participants was set at 15 September 2006. The participating laboratories were requested to analyse the samples employing the methods used in their routine work.The comparison results have demonstrated that in the case of 40K, 54Mn, 60Co, 65Zn, 134Cs, 137Cs and 241Am the participating institutes could produce reliable and comparable analytical results of the highest metrological traceability within ±10% for soil, water and grass samples. However, 109Cd was the most problematic nuclide.It was found that there is a need for corrective action to improve the methodology of correction for matrix effect in the case of this nuclide in a mineral matrix, where a complex interference is present.The analytical uncertainties associated with the results were, in general, appropriate for the analytes and matrices considered in the current comparison.Main text.To reach the main text of this paper, click on Final Report.Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCRI Section II, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).