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Did North Korea really just detonate a hydrogen bomb? Probably not

Big bang in Little China

Kim Jong-un

Analysis At 0130 UTC on Wednesday, the United States Geological Survey recorded a magnitude 5.1 seismic event in North Korea, and shortly afterwards the Nork state media delivered the message that the country had exploded its first thermonuclear device. An H-bomb, in other words.

"Let the world look up to the strong, self-reliant nuclear-armed state," Kim Jong Un, the stout supreme leader of Best Korea, announced on state media.

The Norks have already test fired three atomic weapons, in 2006, 2009 and 2013, but these were your bog-standard nukes, according to Pyongyang, whereas this latest test was of a much more powerful two-stage device. But there are already doubts being raised in the rest of the world.

According to the US government, the seismic data isn't consistent with a thermonuclear device. The tremor caused by this latest test was about the same as the last time North Korea fired off one of its toys, which is definitely not what you'd expect from a thermonuclear device.

The basic atomic weapon is a fission device that either fires two chunks of material, typically types of plutonium, uranium, or neptunium, into each other to set off a chain reaction, or uses carefully coordinated explosives to compress the mass of material and cause fission.

It's a pretty basic technique that's over 70 years old now and isn't terribly efficient – too much of the bomb's mass is wasted and doesn't add to explosive power. The energy released by a fission bomb is typically limited to the energy released by about 500 kilotons of TNT.

Fusion bombs, of the type North Korea claims to have tested, are much more complex devices, with a corresponding increase in explosive force. These use the fission reaction of a basic nuke to compress the weapon's extra fuel into fusion to cause a much larger reaction.

When the US tested its Castle Bravo thermonuclear weapon (less of a bomb, more of a chemical factory with a fuse) the resulting explosion was 15 megatons – about three times larger than expected by its builders.

Given the fact that today's explosion wasn't significantly greater than the last test, experts are highly skeptical that North Korea has pulled off a thermonuclear reaction. While Best Korea develops small devices, there's a limit to how small you can build thermonukes and you'd still expect a much bigger bang.

"We won't know for another few days or weeks whether this was [a hydrogen bomb]," Martin Navias, a defense analyst at King's College London, told CNN. "It doesn't look like one; one would have expected it to be greater if it was an H-bomb."

Even though the test was carried out underground, there should still be some release of radioactivity that can be picked up by monitoring equipment outside of North Korea. The world's scientists are going to be looking for clues of exactly what happened in this latest explosion.

In creating these weapons, North Korea wants to make itself a player on the world stage, but it turns out the biggest threat from its atomic weapons could be to the state itself. These bombs require careful storage to remain safe and it's probable North Korea might be lax in that area.

"There's a lot of other technology needed to accompany such a device and the probability of North Korea knowing that is close to zero," former Los Alamos scientist Dr Robert Brownlee told El Reg.

"My concern is that they will do something that causes damage, or possibly an explosion, and won't be able to discuss it, as no one will want to admit to it. The complications are enormous." ®

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