N. Korean nuclear blast probably less powerful than hoped for: Yale scholar

By Sam Kim
SEOUL, May 28 (Yonhap) -- North Korea apparently failed to achieve desired
explosiveness in its second nuclear test, a Yale University professor says,
citing seismic readings that have been generated by it.

North Korea set off an underground nuclear explosion on Monday, creating a shock
that registered 4.52 in magnitude on the Richter scale, according to a
Vienna-based anti-nuclear weapons organization.
North Korea produced a magnitude of 4.1 in its first test in October 2006, the
Comprehensive Nuclear-Test-Ban Treaty says.
Jefferey Park, director of the Yale Institute for Biospheric Studies, said the
seismic data from Monday's test indicate that North Korea failed to create a
"Hiroshima-class crude explosive device."
"It was too small," he wrote on the Bulletin of the Atomic Scientists, referring
to the explosion.
Using what he called standard conversions, Park, a geologist, said North Korea
appears to have produced a force of 4 kilotons or less through the test that took
place in the northeastern region.
"That's a lot of energy, much larger than the 2006 North Korean test, but it
still falls far short of an expected 12-20 kiloton yield of a crude
Hiroshima-style device," he said. North Korea is believed to have produced less
than 1 kiloton in its previous test.
Park said if North Korea had built a detonator precise enough, it would have
obtained a yield of 10-20 kilotons. One kiloton is equal to 1,000 tons of TNT.
"My guess is that North Korea tried and failed to get a simple plutonium bomb to
detonate correctly," he said.
But he said the latest explosion should not be taken as a failure, warning, "Make
no mistake -- an inefficient nuclear weapon is nothing to dismiss."
"Even at the low end of its estimated yield (2 kilotons), the May 25 test
released as much or more explosive energy than the largest conventional-explosive
air raids during World War II," he said.
samkim@yna.co.kr