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Nuclear Testing Ban Verification

The Comprehensive Test Ban Treaty (CTBT) was adopted in 1996 but has not entered into force yet. This treaty bans "all nuclear explosions" but does not define what constitutes a nuclear explosion. Countries are currently respecting a moratorium on nuclear testing but continue to undertake very-low-yield tests to certify and assess the safety and performances of their nuclear warhead designs. The U.S., France, and the U.K. have adhered to the "zero-yield" standard: all tests where a supercritical fission chain reaction is involved are forbidden. Very-low-yield tests are undertaken in containment vessels, underground which makes their detection and verification off-site near impossible. The absence of technical methods to verify very-low-yield tests, their lack of transparency, and the vagueness of their legal interpretation creates an unstable situation prone to political escalations that can damage the CTBT and the moratorium on nuclear tests. The U.S. has, for instance, accused Russia and China of breaking the zero-yield standard which has triggered dangerous discussions about whether the U.S. should still abide by the nuclear testing moratorium. My research aims at developing technical methods to verify whether very-low-tests involved supercritical fission chain reactions and to devise testing procedures that increase transparency.


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While subcritical tests create fission yields of a few μg TNT equivalent, supercritical tests generate fission yields in the kg range. Fission events during the test generate radioisotopes in concentrations that are proportional to the yield of the test. These radioisotopes continue to emit gamma rays after the test. This project proposes to use on-site gamma spectrum measurements to deduce the fission yield of a past test. These methods could provide effective tools to verify whether a very-low-yield test respected the zero-yield standard.

Verifying Very-low-yield Tests with Gamma Measurements

Collaborators on this project: Frank von Hippel, Christopher Fichtlscherer

Publication: J. de Troullioud de Lanversin, C. Fichtlscherer, Frank N. von Hippel, "Onsite Verification of the Comprehensive Nuclear Test Ban Treaty at Very Low Yields," INMM & ESARDA Joint Annual Meeting, August 23-26

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