Suchergebnisse

Understanding the circumstances of the undeclared 2017 nuclear release of ruthenium that led to widespread detections of the radioisotope (106)Ru in the Eurasian region, and whether it derives from a civilian or military source, is of major importance for society and future improvements in nuclear safety. Until now, the released nuclear material has merely been studied by analyzing short-lived radioisotopes. Here, we report precise measurements of the stable isotopic composition of ruthenium captured in air filters before, during, and after the nuclear release, and find that the ruthenium collected during the period of the 2017 nuclear release has a non-natural isotopic composition. By comparing our results with ruthenium isotopic compositions of spent nuclear fuels, we show that the release is consistent with the isotopic fingerprints of a civilian Russian water-water energetic reactor (VVER) fuel at the end of its lifetime, and is not related to the production of plutonium for nuclear weapons.

Abstract
Pallasites are mixtures of core and mantle material that may have originated from the core–mantle boundary of a differentiated body. However, recent studies have introduced the possibility that they record an impact mix, in which case an isotopic difference between metal and silicates in pallasites may be expected. We report a statistically significant oxygen isotope disequilibrium between olivine and chromite in main group pallasites that implies the silicate and metal portions of these meteorites stem from distinct isotopic reservoirs. This indicates that these meteorites were formed by impact mixing, during which a planetary core was injected into the mantle of another body. The impactor likely differentiated within ∼1–2 Myr of the start of the Solar System based on Hf–W chronology of pallasite metal, and we infer the age of the impact based on Mn–Cr systematics and cooling rates at between ∼1.5 and 9.5 Myr after Ca–Al-rich inclusions (CAIs). When combined with published slow subsolidus cooling rates for these meteorites and considering that several pallasite groups exist, our results indicate that such impacts may be an important stage in the evolution of planetary bodies.