NIST radiochemistry intercomparison program: a summary of four-year performance evaluation study

This paper summarizes the methods currently applied by the National Institute of Standards and Technology (NIST) for the preparation and verification of environmental and radiobioaasay performance evaluation materials for the traceability testing of low-level radioactivity measurements. The evaluation of measurement quality of the all participants indicated that over 90% of the intercomparison results complied with ANSI N42.22 and/or HPS N13.30 standards. Overall, the differences from the NIST values observed for all test nuclides and matrices are less than –7%, with a typical measurement precision better than 10% (1 s). The dependency of measurement quality on the test radionuclides, sample matrices, and radiochemical methods is identified by statistical analyses.