The trace amounts of radioactive isotopes detected not far from North Korea in 2010 were almost certainly not fallout from clandestine atomic testing by the Stalinist state, seismological experts have concluded in a new study due to be released later this month.
Surveillance stations in Russia, South Korea, and Japan in May 2010 documented the presence of small amounts of the radioisotopes barium and xenon. Those measurements along with corresponding weather data led atmospheric researcher Lars-Erik De Greer to postulate the materials resulted from two secret underground atomic detonations. He estimated the explosions took place in April and May 2010, were limited in scale, and equal to the detonation of between 50 and 200 metric tons of TNT.
De Greer's hypothesis never caught on, largely due to the absence during that period of seismic reverberations that would have followed any underground atomic blast.
A forthcoming study in the journal Science and Global Security by a group of Columbia University seismologists further undermines that hypothesis, the university's Earth Institute said on Monday. The study argues that no detonations as large as those suggested by De Greer could have occurred. Such blasts would have been detected by the roughly 100 earthquake monitoring facilities in neighboring South Korea and China, the authors concluded.
"It is important to find confirming evidence for such a serious claim and thus build up support for it, or to find objective and contrary evidence and thus help make the case that the claim is invalid," wrote Columbia seismologists Paul Richards, Won-Young Kim and David Schaff.
The scientists acknowledged they are assuming any attempt by the North to detonate an underground nuclear device would be "well-coupled" with the rock around it instead of set apart in a dug-out hole that would take in the majority of the seismic reverberations. Richards argued it would not be technically feasible to dig out an underground hole large enough to absorb a nuclear blast while also avoiding detection by reconnaissance satellites .
At the most, the North might have set off essentially a "nuclear firecracker" -- a small experiment that would not be useful in developing a nuclear weapon, according to Richards.
North Korea has conducted two nuclear tests to date. The first in 2006 was largely seen as a failure and the second in 2009 was judged to have been moderately more successful. Nuclear weapon experts say Pyongyang must conduct at least one more atomic test if it wants to demonstrate a credible and deliverable nuclear deterrent.
Meanwhile, high-ranking U.S., South Korean, and Japanese diplomats are slated to meet in Tokyo next week for talks on how to handle North Korea, according to a Yonhap News Agency report. Top Japanese atomic envoy Shinsuke Sugiyama is anticipated to update U.S. special envoy for North Korea policy Glyn Davies and South Korean nuclear negotiator Lim Sung-nam on the results of his government's lower-level August meeting with North Korean officials, the Xinhua News Agency reported.