Measurements of stable ruthenium isotopes in nuclear debris samples

Abstract

Ruthenium (Ru) fission product isotopes are important signatures in nuclear non-proliferation and treaty monitoring efforts. However, little is known about the distribution of Ru isotopes contained in samples from nuclear testing activities. This work details the measurement of the stable Ru isotopes ¹⁰⁰Ru, ¹⁰¹Ru, ¹⁰²Ru, and ¹⁰⁴Ru in nuclear debris samples from the Trinity nuclear test. Unusually elevated Ru concentrations are observed in the debris samples when compared to typical crustal abundances, and the isotopic profile reveals that the Ru is fissiogenic in origin. The observed ¹⁰⁴Ru/¹⁰¹Ru and ¹⁰²Ru/¹⁰¹Ru isotopic ratios are clearly different from the expected values based on cumulative fission product yields for ²³⁹Pu fission. Comparison of the observed Ru isotopic ratios with other fission products measured in the samples reveals that the 102 and 104 mass chains are depleted, and suggests that the observed isotopic ratios result from chemical fractionation of volatile precursors during debris condensation. The results represent a promising first characterization of stable Ru isotopes in samples from a nuclear test. Better characterization of source terms will improve future nuclear treaty monitoring efforts by providing a context in which to interpret unknown samples.