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Nuclear Forensics and the North Korean Test

Harold Smith

The power and versatility of nuclear forensics, particularly radio-chemical techniques, could not have been better demonstrated than by its application to the recent underground test in North Korea.[1] Some might have thought that all the debris from the explosion would have been contained in the underground cavity. After all, that was the original purpose of testing underground.

In fact, any nuclear explosion creates radioactive noble gases, notably xenon and krypton, that do not combine with other elements in the geologic structure. Therefore, they can more easily leak to the surface and into the atmosphere where they can be detected beyond national boundaries. Because at least two different gases escape, it is possible for radio-chemists to determine if the fissile material was plutonium or uranium, which of course is exactly what happened. (Press reports said the material was plutonium.)[2] Unfortunately, the chemists cannot determine much more. If there has not been direct venting to the atmosphere, they will not be able to answer the mystery of why Pyongyang’s device seems to have produced such a low nuclear yield, reportedly less than one kiloton, or less than 5 percent of the yield of the Hiroshima and Nagasaki bombs.

The same would not be true if a nuclear weapon were exploded above ground. Then, the debris would be unfiltered, and much more critical information could be obtained, such as the sophistication of its design and whether there exists a stockpile containing fissile material with similar isotopes. The last should be a key consideration for North Korea or any other government that might contemplate providing nuclear materials to terrorists.

Thanks to the inspections associated with implementation of the 1994 Agreed Framework, the International Atomic Energy Agency (IAEA) and/or the United States may possess the isotopic data of the North Korean plutonium. North Korea must be made aware that use of its fissile material can be traced to Pyongyang and that it must anticipate the retribution that would follow if any of its weapons or fissile material should be used by any of its accomplices or customers. Perhaps, this is the time for the Bush administration to speak directly to the North Korean government and make this clear.

Pyongyang might conclude that President George W. Bush was not making an idle boast when he said October 9 that “the transfer of nuclear weapons or material by North Korea to states or non-state entities would be considered a grave threat to the United States, and we would hold North Korea fully accountable of the consequences of such action” One can hope, therefore, that forensic science combined with strong and credible diplomacy can deter North Korea from passing plutonium to terrorists or to other countries.

Harold Smith is a distinguished visiting scholar and professor at the Goldman School of Public Policy, University of California at Berkeley. He served as assistant to the secretary of defense for nuclear, chemical, and biological defense programs during the Clinton administration.


1. For more information on nuclear forensics, see William Dunlop and Harold Smith, “Who Did It? Using International Forensics to Detect and Deter Nuclear Terrorism,” Arms Control Today, October 2006, pp. 6-10.

2. David Sanger, “North Korean Fuel Identified as Plutonium,” The New York Times, October 17, 2006, p. A-11.