Akihiko Yokoyama (Japan): Development of a Neptunium Standard Material for Mass Spectrometry

Recently the techniques of highly sensitive mass spectrometry underwent rapid development. Especially, for long-lived actinide nuclides, the techniques are becoming more and more important as a promising alternative of radioactivity measurements. A tracer nuclide to determine the chemical recovery, which does not exist in nature and which is not contained in target samples, is absolutely necessary for that purpose. An isotopic tracer for environmental neptunium-237, however, has not yet been developed. We are looking for an efficient method for the production of ²³⁶Np as a candidate. This tracer could be produced via various nuclear reactions, but might be contaminated by ²³⁷Np, disturbing the measurement of ²³⁷Np in environmental samples. Up to date, the appropriate production conditions of ²³⁶Np are not known. We are now on the way to determine the cross sections of 236Np and the isotopic ratios of ²³⁶Np/²³⁷Np produced in the reactions of ²³⁸U + p and ²³²Th + ⁷Li.