Nature 382, 528 - 531 (08 August 1996); doi:10.1038/382528a0

Trace gas emissions on geological faults as indicators of underground nuclear testing

C. R. Carrigan^*, R. A. Heinle^*, G. B. Hudson^†, J. J. Nitao^* & J. J. Zucca^‡

^* Geosciences and Environmental Technologies Department (L-206),
^† Isotope Sciences Division (L-231) and ^‡ Geophysics and Global Security Department (L-205), Lawrence Livermore National Laboratory, PO Box 808, Livermore, California 94550, USA

UNDERGROUND nuclear explosions produce trace amounts of distinctive but ephemeral radionuclide gases. In the context of monitoring a comprehensive test ban treaty, the detection of these gases within the territory of a signatory, during a challenge inspection¹⁻⁵, may indicate the occurrence of a clandestine nuclear event. Here we report the results of an experiment simulating a well-contained underground nuclear explosion, undertaken to test the ability of natural gas-transport processes to move highly dilute and rapidly decaying radionuclides to the surface. We find that trace gases are transported to the surface within periods of weeks to a year, by flow along faults and fractures driven by barometric pressure variations. Both our observations and related simulations exhibit a chromatographic behaviour, with gases of higher atomic mass and lower diffusivity reaching the surface more rapidly. For a 1-kilotonne nuclear test under conditions identical to those of our experiment, we predict that short-lived ¹³³Xe and ³⁷Ar would be detectable, respectively, about 50 and 80 days after the detonation. Our results indicate that radionuclide sampling along natural faults and fractures, as a forensic tool, can be an extremely sensitive way to detect nearby underground nuclear explosions that do not fracture the surface.

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