资源环境科技发展态势分析平台

Isotopic ratios of radioactive releases into the environment are useful signatures for contamination source assessment. Uranium is known to behave conservatively in sea water so that a ratio of uranium trace isotopes may serve as a superior oceanographic tracer. Here we present data on the atomic U-233/U-236 ratio analyzed in representative environmental samples finding ratios of (0.1-3.7).10(-2). The ratios detected in compartments of the environment affected by releases of nuclear power production or by weapons fallout differ by one order of magnitude. Significant amounts of U-233 were only released in nuclear weapons fallout, either produced by fast neutron reactions or directly by U-233-fueled devices. This makes the U-233/U-236 ratio a promising new fingerprint for radioactive emissions. Our findings indicate a higher release of U-233 by nuclear weapons tests before the maximum of global fallout in 1963, setting constraints on the design of the nuclear weapons employed.