Extending the Set of Environmental Anthropogenic Radionuclide Tracers

Anthropogenic radionuclides have been released into the environment either by atmospheric nuclear weapons tests, nuclear accidents or from the nuclear fuel cycle. The fission products ⁹⁹Tc, ¹³⁵Cs and the actinide isotopes ²³⁶U and ²³⁷Np are considered promising oceanographic tracers due to their expected conservative behaviour in seawater. Accelerator Mass Spectrometry (AMS) has proven to be a powerful technique for the detection of these long-lived anthropogenic radionuclides with highest sensitivity, especially for ²³⁶U and ²³⁷Np. However, the quantitative analysis of ²³⁷Np by mass spectrometric techniques is hampered by the lack of an isotopic spike. Within a joint project with the University of Tsukuba we investigated options to produce a ²³⁶Np spike material to overcome this problem. For oceanographic studies, the different source terms need to be identified to determine the distribution pathways to the sampling station. We recently proposed the U isotope signature ²³³U/²³⁶U as a fingerprint to differentiate between sources of anthropogenic U. However, a careful characterization of the main sources of ²³³U is first required first. Our present understanding of the ²³³U production paths will be introduced in my talk as well as a description of the produced Np spike material. The quantitative analysis of fission products such as ⁹⁹Tc remains challenging due to the interfering background induced by stable isobars, i.e. ⁹⁹Ru in the case of ⁹⁹Tc. The current status of fission product analysis using the new technique of Ion-Laser-Interaction Mass Spectrometry (ILIAMS) at the Vienna Environmental Research Accelerator (VERA) will be presented.