Bombs Below

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Science  18 Jan 2013:
Vol. 339, Issue 6117, pp. 253
DOI: 10.1126/science.339.6117.253-c

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The political ramifications of clandestine underground nuclear tests are often severe. Therefore, methods must be developed to reliably verify when a test has been completed, without generating false positives. Radiogenic xenon (Xe) is one such tracer produced by nuclear explosions either directly as a fission product or indirectly from unstable iodine precursors; however, it is also generated by nuclear power plants and during the production of radioisotopes for medical use. These sources have different ratios of four Xe isotopes when measured in gas samples, so that there is a typical isotopic range assumed for a weapons test. By incorporating radioactive decay into subsurface transport modeling of the Nevada Test Site in the United States, Lowrey et al. suggest that this range may be too narrow. For example, some simulations showed that some signals could be produced by the decay of precursor radioiodine exclusively. More generally, differential transport caused by variations in atmospheric pressure can strongly influence Xe isotopic ratios. Based on their simulations, the Xe signal from the 26 March 1992 test would have met previous criteria for a nuclear weapon only if the test had taken place at certain locations within the Nevada Test Site.

Geophys. Res. Lett. 10.1029/2012GL053885 (2012).

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