Hot particles, radioactive particles of nuclear fallout and radioactive waste, also exhibit distinct isotopic signatures. Their radionuclide composition (and thus their age and origin) can be determined by mass spectrometry or by gamma spectrometry. For example, particles generated by a nuclear blast contain detectable amounts of Co and Eu. The Chernobyl accident did not release these particles but did release Sb and Ce. Particles from underwater bursts will consist mostly of irradiated sea salts. Ratios of Eu/Eu, Eu/Eu, and Pu/Pu are also different for fusion and fission nuclear weapons, which allows identification of hot particles of unknown origin.
Uranium has a relatively constant isotope ratio in all natural samples with ~0.72%  some 55 ppm  (in secular equilibrium with its parent nuclide ) and the balance made up by . Isotopic compositions that diverge significantly from those values are evidence for the uranium having been subject to depletion or enrichment in some fashion or of (part of it) having participated in a nuclear fission reaction. While the latter is almost as universally due to human influence as the former two, the natural nuclear fission reactor at Oklo, Gabon was detected through a significant diversion of  concentration in samples from Oklo compared to those of all other known deposits on earth. Given that  is a material of proliferation concern then as now every IAEA-approved supplier of Uranium fuel keeps track of the isotopic composition of uranium to ensure none is diverted for nefarious purposes. It would thus become apparent quickly if another Uranium deposit besides Oklo proves to have once been a natural nuclear fission reactor.