What’s the Difference Between an A-Bomb and an H-Bomb?

Why North Korea’s alleged nuclear test is drawing skepticism and fear alike

The first hydrogen bomb was detonated by the United States in a test over the Marshall Islands in 1952. SuperStock/Corbis

North Korea’s new claims that it has tested a hydrogen bomb is drawing both fears and skepticism from politicians and experts. While North Korea isn’t a nuclear superpower by any means, it’s been generally accepted that the tiny dictatorship probably has a few nuclear warheads in its possession, albeit lacking the missile technology necessary to launch them. So why are people so worried by North Korea claiming it tested an H-bomb?

Like other weapons, not all nukes are made equally. And while atomic bombs like the two dropped on Hiroshima and Nagasaki during World War II are extremely destructive, hydrogen bombs can be at least 1,000 times stronger than their predecessors, The Globe and Mail reports.

Although the atomic bombs of World War II, which went by the code names Little Boy and Fat Man, used different fuels and triggering mechanisms, they were both fission bombs. This means that they harnessed the energy released by splitting either uranium or plutonium atoms. Hydrogen bombs, on the other hand, are fusion devices. Instead of blasting atoms apart, H-bombs slam isotopes of hydrogen together that sets off a chain reaction, making for much more energy-efficient and destructive explosions.

“Think what’s going on inside the sun,” Takao Takahara, professor of international politics and peace research at Meiji Gakuin University, tells Yuri Kageyama for the Associated Press. “In theory, the process is potentially infinite. The amount of energy is huge.”

Because hydrogen bombs (also called “thermonuclear bombs”) use fusion, they can be much, much smaller than atomic bombs. While Little Boy and Fat Man were so big that they required dedicated bombers to fly them to their targets, the North Koreans are aiming to develop a hydrogen bomb that could be installed on a missile, John Carlson, former head of Australian Safeguards and Non-Proliferation Office, tells Michael Safi for The Guardian.

Hydrogen bombs are so much more powerful than their predecessors, so it’s much harder and difficult to make one. The sheer amount of energy involved is enormous—basically that of an atomic bomb. This fact has left some experts skeptical of North Korea’s claims, Anna Fifield reports for the Washington Post.

As Middlebury Institute of International Studies nuclear expert Jeffrey Lewis wrote for 38 North in December regarding rumors of a North Korean H-bomb:

“Thermonuclear weapons are tricky; making one work requires a bit of test experience...A more technically plausible scenario is that North Korea might be experimenting with fusion fuels, such as deuterium or lithium, to boost the yield of a fission explosion.”

While it would be very difficult for North Korea to make a hydrogen bomb, it isn’t impossible. However, for now international experts limited information to go off of, and the size of the blast was likely not large enough to come from an H-bomb, Fifield reports. 

If this was in fact an H-bomb test, scientists will know more once they have had time to analyze seismic readings and tested for radioactive gases around the site. But for now, it might be worth taking the news with a grain of salt.

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