N. Korea nuke program still a mystery
BY WILLIAM J. BROAD, New York Times
As scientists and world leaders scrambled Tuesday to judge the importance of North Korea's claim that it had detonated a third nuclear bomb, the main thing that quickly became evident is how little is known about the country's increasingly advanced atomic and missile programs.
Even the best news about the test -- that it was small by world standards -- could have a dangerous downside if the North's statement that it is learning to miniaturize bombs is true. That technology, which is extremely difficult to master, is crucial to being able to load a weapon atop a long-range missile that might one day reach as far as the U.S. mainland.
"We don't know enough to nail it, but we can't rule out that they've done something dangerous," Ray E. Kidder, a scientist who pioneered early nuclear warhead designs at the Livermore weapons lab in California, said of the underground test.
As is usual with tests by the secretive North, it was not even clear if the underground test was nuclear, as opposed to conventional bomb blasts meant to mimic an underground nuclear test. Experts assume it was nuclear partly from the shape of its seismic signal.
It also remains unclear whether the North used plutonium or enriched uranium to fuel the bomb. U.S. officials believe that the country's previous two nuclear tests, in 2006 and 2009, used plutonium, and they fear a switch to uranium will allow the country a faster and harder-to-detect path to a bigger arsenal.
While scientists are actively hunting for the airborne markers of a uranium test, it is not certain that gases needed to make that judgment escaped the test site.
Scientists said the relatively small size of Tuesday's blast calmed, at least temporarily, their worst fears: that the North's recent references to more powerful hydrogen bombs indicated the possibility that it might have at least enough technology to try to test one.
Those bombs, nicknamed city-busters, are roughly 1,000 times stronger than atom bombs. If the North were to get them it would represent an enormous leap in its known capabilities. The first U.S. hydrogen bomb to be tested caused the Pacific island of Elugelab to vanish.
What emerged most clearly Tuesday from sensitive global networks that measure faint rumbles in the earth was that the underground blast was most likely larger than North Korea's past explosions.
In Vienna, the preparatory commission for the Comprehensive Nuclear Test Ban Treaty Organization, which runs a global seismic network, said the blast measured 5.0 in seismic magnitude. The U.S. Geological Survey put its own estimate at 5.1 in magnitude.