Simple and fast method for the analysis of 236U, 237Np, 239Pu and 240Pu from seawater samples by Accelerator Mass Spectrometry.

ABSTRACT

A simple and fast radiochemical procedure for the sequential extraction of U, Np and Pu from small-volume seawater samples (<10 L) is presented. The method has been developed and optimized for the final determination of 236U, 237Np, 239Pu and 240Pu by Accelerator Mass Spectrometry (AMS). It is based on the use of 242Pu as tracer for both Np and Pu isotopes. Samples are pre-concentrated by Fe(OH)2 co-precipitation. TEVA® and UTEVA® resins are used in a very simplified way for the final purification of the Pu+Np and U fractions, respectively. The radiochemical yields of the three elements have been investigated in detail by alpha spectrometry (AS) and gamma spectrometry (GS). The obtained results indicate high and robust chemical yields for the three elements and similar ones for Pu and Np. Furthermore, the use of 242Pu as tracer for 237Np is validated by analyzing a reference seawater sample (IAEA-443) by radiometric techniques. We demonstrated that, if chemicals are properly chosen, processed blank levels can be kept at the same level of the extremely low detection limits that can be achieved by AMS (105-106 atoms/sample). The procedure is finally applied for the study by AMS of a reference seawater sample from the Mediterranean Sea (IAEA-418).