UNIDENTIFIED WOMAN: (Speaking Korean).
AUDIE CORNISH, HOST:
That was an North Korean state television news reader announcing the country had tested a hydrogen bomb. If true, it would be a first for Pyongyang. Now, this afternoon, the White House cast doubt on the ability of the isolated nation to test such an advanced weapon. Here's Press Secretary Josh Earnest speaking to reporters.
(SOUNDBITE OF PRESS CONFERENCE)
JOSH EARNEST: The initial analysis that's been conducted of the events that were reported overnight is not consistent with North Korean claims of a successful hydrogen bomb test.
CORNISH: Coming up, we'll speak to a former State Department official about what North Korea hopes to gain by conducting the nuclear test. First, joining me in the studio is NPR science correspondent Geoff Brumfiel to talk about the claims from Pyongyang. Geoff, welcome to the studio.
GEOFF BRUMFIEL, BYLINE: Thank you.
CORNISH: The White House sounds fairly confident there that this was not a hydrogen bomb test. What are they basing this on?
BRUMFIEL: Well, when a nuclear weapon is tested, it sends off a shockwave through the earth. It's basically like an earthquake. And seismic stations around the world can pick that up, and they can make some sort of estimate about the size. Based on what was observed, the unofficial estimates by the Pentagon say this was under 10 kilotons. That's 10,000 tons of TNT-equivalent explosives. But the bottom line is that seems too small to be a hydrogen bomb. Just for comparison here, the first hydrogen bomb was 10 megatons. That's 10 million tons of TNT - a thousand times more powerful. It would make this thing look like a firecracker.
CORNISH: We should note that North Korea has, as far as what's known, tested three atom bombs. Now, what makes hydrogen bombs harder to build?
BRUMFIEL: There's basically two ways to make a nuclear explosion. You can either split apart heavy atoms like uranium and plutonium, and that splitting apart, called fission, releases energy. Or you can fuse together light atoms such as hydrogen. That's where the hydrogen bomb comes from. Causing those atoms to stick together is a lot harder than splitting them apart. In fact, you have to set off a fission bomb to make a hydrogen bomb work, so it's technically much more complicated.
CORNISH: So if this wasn't an H-bomb, what was it? I mean, could it have been a replica of the previous atom bomb test?
BRUMFIEL: Yeah, it could have been a standard nuclear bomb. And I don't want to - I say standard. That kind of downplays it. I mean, this would still be a bomb roughly the size of those used on Hiroshima and Nagasaki, so this is still a very serious thing. But there is another possibility, which is that North Korea put a little bit of hydrogen at the center of their bomb, and then they used that hydrogen to enhance the fission bomb. That would allow them to claim they had conducted an H-bomb test even though it wasn't quite what we would consider a hydrogen bomb.
CORNISH: We know what the White House thinks, but in the end, how will the international community verify what happened?
BRUMFIEL: Well, we may never be able to say much more, but there is a possibility that radioactive gases will leak out. These tests are conducted underground, and so we have to wait for that to happen. It could take days or even weeks. There are monitoring stations all around North Korea in Russia, China, places like that. And if they pick something up, if they catch a whiff, we may learn more about exactly what happened.
CORNISH: That's NPR science correspondent Geoff Brumfiel. Geoff, thanks.
BRUMFIEL: Thank you.