Measurement of the half-life of the nuclear waste product samarium-151

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In close collaboration with scientists from various European laboratories, JRC scientists produced better decay data of the long-lived radionuclide samarium(Sm)-151. This work contributes to an improved radiological characterisation of nuclear waste.

It is imperative that the thousands of tonnes of low and intermediate level radioactive wastes arising each year from the decommissioning of nuclear facilities and the clearance of sites are disposed of in a manner that is safe, secure, socially-acceptable, and cost-effective. Key metrological problems must be addressed if the nuclear industry is to achieve these goals. The JRC-Institute for Reference Materials and Measurements (IRMM) supports the measurement system through the development of radioactivity standards, decay data, reference materials and detection methods for radioactive waste measurements. Only accurate and traceable measurements will ensure that waste is well characterised, consigned to the correct waste stream and its radiological impact, accurately modelled.

The JRC-IRMM collaborated with European laboratories to determine the half-life of samarium-151, which is a relatively long-lived radionuclide with a half-life of almost a century. It is produced by the fission process in nuclear reactors, and therefore also present in the nuclear waste. Measurements performed in the past were not very accurate and showed discrepancies. With the newly determined half-life value of 94.6 ± 0.6 years, the uncertainty on the reference value could be reduced by an order of magnitude. Also, the precise activity measurements produced in this work have been used to establish the international equivalence of the Becquerel for this radionuclide via the ‘Système International de Référence’ (SIR), which is operated by the Bureau International des Poids et Measures (BIPM) in Paris.

Read more in: M.-M. Be et al.: “Determination of the 151Sm half-life“, Radiochim. Acta 103 (2015) 619-626, doi: 10.1515/ract-2015-2393.