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

TL;DR

This paper introduces a rapid, simplified radiochemical method for extracting and analyzing ultra-trace levels of uranium, neptunium, and plutonium isotopes in seawater using Accelerator Mass Spectrometry, with high chemical yields and low detection limits.

Contribution

The authors developed and validated a streamlined, efficient procedure for the simultaneous extraction and AMS analysis of specific actinides from small seawater samples, improving speed and sensitivity.

Findings

High and robust chemical yields for U, Np, and Pu.

Validated use of $^{242}$Pu as a tracer for $^{237}$Np.

Detection limits of $10^5 - 10^6$ atoms per sample.

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 $^{236}$U, $^{237}$Np, $^{239}$Pu and $^{240}$Pu by Accelerator Mass Spectrometry (AMS). It is based on the use of $^{242}$Pu 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 $^{242}$Pu as tracer for $^{237}$Np 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 ($10^5 - 10^6$ atoms/sample). The procedure is finally applied for the study by AMS of a reference seawater sample from the Mediterranean Sea (IAEA-418).