Yes, North Korea Probably Tested an H-Bomb — Just Not the Kind You’re Thinking Of

The rumbling started early Wednesday morning when a small earthquake was detected near a known nuclear test site in North Korea. Not long after, North Korean state media broadcast the announcement that the country had successfully tested a small hydrogen bomb. The alarming headlines that followed could mostly be divided into two categories: The North Koreans are delusional and there's no way they have H-bombs, or we're all gonna die.

Here are the facts as we now know them: North Korean state media has insisted that the test was of a hydrogen bomb, and monitoring stations around world picked up seismic activity consistent with a small-yield nuclear test coming from an area where the North Koreans have done all their previous nuclear bomb testing.

Based on the available information, the North Koreans may not be entirely full of crap. But they're not entirely 100 percent above board, either. The issue is that the difference between the two kinds of nuclear weapons — A-bombs and H-bombs, also known as thermonuclear bombs — is highly nuanced.

In the conventional understanding, there are two types of bombs: fission and fusion. Although they have nearly identical (and easily confused) names, they represent almost a 180-degree difference in their approach to blowing stuff up. Fission weapons use a particular isotope of a heavy, sort of unstable chunk or metallic uranium or plutonium. Some sort of trigger is used to kick off a chain reaction that splits each atom of stuff into two smaller atoms, neutrons, and miscellaneous energy. The neutrons smash into other atoms, causing them to split. Basically, the atom-splitting turns into a chain reaction splitting off even more atoms that throws off tons of energy. Fission equals splitting.

Related: North Korea Claims It Just Successfully Detonated a Hydrogen Bomb

The other flavor of nuclear reaction is fusion. Fusion takes two of the tiniest of atoms and smashes them into each other with incredibly high energy. They fuse to make a larger atom, throwing off neutrons and energy, which in turn can fuse more stuff together. Thus, fusion equals combining.

Like fission, fusion can become a self-sustaining chain reaction under the right conditions. When people say "atom bomb," they mean a fission device using uranium or plutonium. Likewise, when people say "hydrogen bomb," they mean a fusion device using various hydrogen isotopes.

In this telling, fission weapons (A-bombs) are considered small or low-yield, meaning they generate explosions equivalent to tens or hundreds of thousands of tons (kilotons) of TNT. Fusion weapons (H-bombs) are much bigger weapons with explosive yields tens or hundreds of times larger, reaching up to tens of millions of tons (megatons) of TNT.

But the reality of it isn't nearly so clear cut. There are pure fission devices, fission-fusion devices, boosted fission, fission-fusion-fission devices, salted warheads — all kinds of stuff, and that's long before you get into the genuinely esoteric designs.

Some observers will claim that something only counts as an H-bomb if it gets a big chunk of its explosive energy from fusion reactions. The kind of H-bombs that produce blasts in the megaton range certainly produce a sizeable portion of their energy from fusion reactions. Others, however, might claim that it's an H-bomb if it uses hydrogen isotopes for the bomb part, regardless what contributes what portion of the final energy.

If you use the first definition — that a lot of the energy comes from fusion reactions — then you're talking classic H-bomb. That generally means a classic 1950s "duck and cover" city buster of a thermonuclear bomb that could flatten an entire city in one blow. For sake of simplicity, I'm just going to call this kind of H-bomb a "big H-bomb."

Related: Kim Jong-un Says North Korea Has an H-Bomb — But No One Believes Him

But if you use the second definition (hydrogen isotopes were harmed in the making of this explosion), then you could be talking about a huge range of yields, from the teeny tiny to the impressively large. This, among other things, covers "boosted fission devices," which are mostly fission, but use hydrogen isotopes to juice things up. For simplicity, we'll call the whole class of weapons that use fusion but don't rely on fusion to directly fuel the bang "small H-bombs."

So what's the practical difference between 10,000 tons of TNT versus 1,000,000 tons of TNT? If you run a quick-and-dirty simulation, a 10 kiloton North Korean nuke detonated 1,000 meters over downtown Seoul produces 78,000 fatalities and somewhere around 270,000 estimated injuries. But if you hit that same target with a good old-fashioned high-yield weapon of 1 megaton, you get something closer to 1,625,000 dead right off the bat, with another 4,725,000 injured. In other words, complete and utter devastation.

Watch the VICE News documentary Launching Balloons into North Korea: Propaganda Over Pyongyang:

From a design standpoint, H-bombs (of whatever type) are, in a sense, both more efficient and more complex. To be sure, the practical difference between big and small H-bombs isn't that one is exactly nicer to get hit with, but the big H-bombs certainly are a lot worse.

Now, the big five nuclear powers — the US, Russia, China, France, and the UK — they've probably mastered the whole range of nuclear weapons, from A-bombs to both types of H-bombs. The up-and-coming nuclear powers — India, Pakistan, and Israel — may have a grasp on certain types of H-bomb technology, but it's difficult to say what they do or don't have.

The important point here is that small H-bombs are probably easier to make than most people realize. As Andre Gsponer of the Independent Scientific Research Institute in Switzerland wrote in 2008, "[Small H-bomb technology] is relatively easy to implement." That technology, he said, has "a number of significant technical and military advantages, which explain why it is used in essentially all militarized nuclear weapons, including in India, Pakistan, and North-Korea."

So the question is less about whether or not the North Koreans are tossing hydrogen isotopes into the mix when making their nukes, but the particular way they're folding that fuel into the mix and whether they're making big H-bombs or small H-bombs.

Related: North Korea Has Nukes and Missiles — But Does That Mean It Has Nuclear Missiles?

The US — along with South Korea, China, and others — seems to think North Korea is definitely full of shit. The White House said Wednesday its initial analysis of the blast in North Korea is "inconsistent" with claims of successful hydrogen bomb test. Beijing's state media has also said it "cannot support" claims of an H-bomb test, and that further analysis required. But because the test was conducted underground, thus concealing many of the tell-tale traces that could be used to get a clearer picture of the bomb design, it may not be possible to conclusively determine what kind of device was used.

Another part of the equation — one that has been largely overlooked — is the issue of how North Korea would launch its nuclear weapon. Big H-bombs require big rockets, which North Korea doesn't really have. If the North Koreans really have great big H-bomb, then, in effect, they don't have any nuclear missiles, because none of their missiles have the ability to sling a giant bomb halfway around the planet. On the other hand, if the North Koreans can field even a mediocre missile, they could conceivably use it to launch a smaller, lighter nuclear device, effectively turning their missiles into nuclear missiles. In that scenario, the greater efficiency of an H-bomb becomes a key factor for North Korea's mad scientists.

Jeffrey Lewis, a top-notch nuke wonk at the Center for Nonproliferation Studies, told VICE News that a boosted fission weapon is "the most likely scenario in my view, with a failed thermonuclear test a close second." Meaning that it's probably a small H-bomb they're trying to test, but it could also be that they just haven't ironed out all the kinks in making big H-bombs quite yet.

The state of North Korea's missile program means they'd likely have a hard time hitting the US if they did have a big H-bomb, but that's a cold comfort if they just want to nuke Seoul or Tokyo.

Of course, this is all based on publicly available, unclassified information. The only way to be really sure about what happened is to detect specific trace amounts of radioactive material produced by the blast. But since the North Koreans were polite enough to hold their test below ground — thus avoiding spewing fallout everywhere — all of those useful radioactive clues are trapped deep within the Earth.

But based on what we know so far, here's the bottom line: North Korea probably tested an H-bomb, just not the kind of H-bomb you're thinking of.

Follow Ryan Faith on Twitter: @Operation_Ryan