k₀-NAA, a valuable tool for reference-material producers

The main concern of producers of certified reference materials (CRM) is the preparation of high-quality products with demonstrated homogeneity and stability, combined with a well established set of certified characteristics. CRM producers must, furthermore, comply with other constraints imposed by the ISO Guide 34: • production processes, production control, and certification analyses should be performed by expert laboratories, using validated protocols documented in their respective quality assurance manuals; • laboratory mean values and the corresponding "expanded" uncertainties, must be used for the determination of the certified values, as recommended by the ISO Guide to the Expression of Uncertainties in Measurements (GUM); and • when possible, traceability of the certified value to the SI units, using appropriately validated and/or primary methods, must be ensured. k₀-NAA, i.e. neutron activation analysis with k₀ standardization, is one of the analytical techniques implemented at the Reference Material Unit of IRMM; it meets the first two requirements.