Abstract and subjects
An optimized method was developed to analyze environmental soil and sediment samples for Np-237, Pu-239, and Pu-249 by ICP-MS using a Pu-242 isotope dilution standard. The high yield, short time frame required for analysis, and the commercial availability of the Pu-242 tracer are significant advantages of the method. Control experiments designed to assess method uncertainty, including variation in inter-element fractionation that occurs during the purification protocol, suggest that the overall precision for measurements of Np-237 is typically on the order of +/- 5%. Measurements of the Np-237 concentration in a Peruvian Soil blank (NIST SRM 4355) spiked with a known concentration of Np-237 tracer confirmed the accuracy of the method, agreeing well with the expected value. The method has been used to determine neptunium and plutonium concentrations in several environmental matrix standard reference materials available from NIST: SRM 4357 (Radioactivity Standard), SRM 1646a (Estuarine Sediment) and SRM 2702 (Inorganics in Marine Sediment). (C) 2015 Elsevier Ltd. All rights reserved.