Experts continue to doubt North Korean hydrogen bomb claims

New York Times : North Korea’s claim that it tested a hydrogen thermonuclear device earlier this week is being questioned by international experts. Among other things, they have pointed out the significant difference in seismic effect between the North Koreans’ test and previous H-bomb tests conducted by the US and Russia. The North Korean test registered only magnitude 4.8, which is thousands of times less powerful than the magnitude 6.8 registered during a 1971 American test. South Korea estimates that the test yielded only a 6-kt explosion, about 2.5 times less powerful than the 15-kt atomic bomb dropped on Hiroshima. Several international experts have suggested that maybe North Korea tested a “boosted” atomic bomb, in which a small amount of tritium is added to the core. The addition of the heavy hydrogen results in a minor thermonuclear reaction, modestly increasing a bomb’s power. However, such a boosted bomb does not have the same effect as a true thermonuclear bomb. Because of the small size of the explosion, it may be impossible to tell whether the object in question was an atomic bomb, a boosted bomb, or a very small thermonuclear bomb. Similar ambiguity surrounds a 1998 underground test performed by India, during which an explosion of just a few dozen kilotons was measured. The only nations with confirmed thermonuclear weapons are China, France, Russia, the UK, and the US.