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The New York Times is reporting [nytimes.com] a claim made by the North Korean government in which is says that it has detonated a hydrogen bomb:
a claim that, if true, would dramatically escalate the nuclear challenge from one of the world’s most isolated and dangerous states.
In a brief announcement, about an hour after seismic detectors around the world picked up a 5.1 magnitude seismic event along the country’s northeast cost, officials said that the test was a “complete success.” But it is difficult to tell whether that boast is true, and it may be weeks or longer before detectors sent aloft by the United States and other powers can determine what kind of test was conducted.
The apparent North Korean test took place at or near the Punggye-ri nuclear test site, where the three previous tests have been conducted over the past nine years. But if the North Korean claim is true, this one was of a of a different nature.
Like most of the rest of the world who know something about the physics of these devices, I'm very skeptical of this claim, given that, even on a slow news day, the North Korean government has about as much credibility as the boy who cried wolf.