A paper in the March issue of the journal Science & Global Security titled "Radionuclide Evidence for Low-Yield Nuclear Testing in North Korea" by Lars-Erik De Geer, Research Director at the Swedish Defence Research Agency claims that North Korea may have carried out a very low-yield nuclear weapon test explosion in May 2010. North Korea is known to have conducted a nuclear test explosion in 2006 and again in 2009.
The paper says that radionuclide data collected between 14 and 23 May 2010 at stations in South Korea, Japan and Russia suggest that North Korea carried out a very low-yield underground nuclear test on 11 May 2010.
If there was a nuclear explosion in May 2010, it was not detected by any seismic station or network. This leads De Geer to argue that if there was a nuclear detonation, it "must therefore have been quite low-yield..." according to a prepublication draft of the article.
De Geer also notes that if such an event was "still detected by another technology in the currently evolving CTBT verification system as well as by a national control post [it] suggests that there are fewer and fewer ground for countries to refuse ratifying the CTBT by questioning the effectiveness of its verification regime. It also shows that the CTBT verification system sometimes is capable of detecting underground nuclear tests of significantly lower yields than what was anticipated when the treaty was opened for signature 15 years ago."
De Geer speculates that North Korea is trying to build a more powerful, tritium-boosted nuclear bomb through low-yield tests.
See press release on the paper here.
However, De Geer's conclusions about the radionuclide data and further North Korean nuclear testing are not shared with other nuclear test monitoring experts.
Frank von Hippel, a physicist at Princeton University in New Jersey, told Geoff Brumfiel at Nature that De Geer’s analysis provides convincing evidence of some kind of nuclear fission explosion. But, Brumfiel writes, von Hippel does not agree that it involved two weapons tests or a fusion boost. "I hope that other experts will analyse it and see whether they can put forward alternative, simpler explanations," von Hippel said.
Brumfiel also reports that:
"Others remain deeply sceptical that the tests took place at all. Most troubling is the lack of any seismic vibrations to support the radioisotope data, according to Ola Dahlman, a retired geophysicist who spent years working with the test-ban group's detection network. The Korean peninsula is wired to spot the tiniest shake from a nuclear explosion, Dahlman says. 'It should have been able to see something.'"
The data analyzed in the De Geer study were produced by the CTBTO’s network of sensors, but the organization itself has never officially analyzed all these data, according to Lassina Zerbo, director of the data centre in Vienna that handles the sensor network.
Zerbo told Nature that although the data are processed and shared quickly after such an event, formal analyses are done only if requested by the CTBTO's member states. None of the 182 signatories to the treaty ever made such a request, he said.
Zerbo added that the organization does not have access to the South Korean data mentioned in the paper, which was collected by that South Korea's own national network of monitoring stations.
Zerbo told Nature that it may indeed prompt scientists in CTBTO member states to re-examine the data — and then possibly to ask the CTBTO to conduct a formal analysis.
ACA's Research Director Tom Z. Collina concludes in a new column at www.armscontrolnow.org that: "If this indeed was a nuclear test, its raises important new questions about North Korea’s nuclear weapons program, but not about the CTBT verification system."
For more on the test ban verification and monitoring issues, see: http://www.projectforthectbt.org/verification