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Science

Nuclear bombs: Thermonuclear vs atomic

Lewis Sanders IV
September 3, 2017

North Korea has claimed significant advances in testing a thermonuclear bomb. But how is it different to an atomic bomb? DW takes a look at the fundamental differences between two of history's most destructive weapons.

https://p.dw.com/p/2jH8L
Developed by the US, the first thernomuclear bomb was fired on Elugelab Island in 1952. It left a massive underwater crater where the island had once been.
Developed by the US, the first thermonuclear bomb was fired on Elugelab Island in 1952. It left a massive underwater crater where the island had once been.Image: picture-alliance/dpa/US Department of Energy

North Korea announced on Sunday that it had conducted a nuclear test using an advanced hydrogen bomb, also known as a thermonuclear bomb, marking departure from its experiments with first generation atomic weapons. But what's the difference between an atomic bomb and the more advanced hydrogen bomb?

Read more: North Korea: From war to nuclear weapons

Detonation

The fundamental difference between a hydrogen bomb and atomic bomb is in the detonation process. For an atomic bomb, such as the ones dropped on Nagasaki and Hiroshima, its explosive power is a result of the sudden release of energy upon splitting the nuclei of a heavy element, such as plutonium. This process is known as fission.

Fission and fusion

Years after the first atomic bomb was developed in New Mexico, the US developed a weapon that relied on the technology of the atomic bomb, but expanded the detonation process to create a stronger explosion. That weapon is called a thermonuclear bomb.

For a thermonuclear bomb, the detonation process comprises several parts, beginning with the detonation of an atomic bomb. The first explosion creates temperatures of millions of degrees, providing enough energy to force the two light nuclei close enough to combine in a second stage known as fusion.

Shape

According to experts, North Korea's latest bomb showed a marked difference from previous ones, displaying a chambered device that suggests a two-stage hydrogen bomb.

"The pictures show a more complete form of a possible hydrogen bomb, with a primary fission bomb and a secondary fusion stage connected together in an hourglass shape," said Lee Choon-geun, senior research fellow at the state-run Science and Technology Policy Institute in South Korea.

Infographic showing nuclear explosions over past century

Power

The yield of a thermonuclear bomb can be hundreds to thousands of times more powerful than the atomic bomb.

Read more: North Korea crisis: 10 questions, 10 answers

The explosive power of an atomic bomb is often measured in kilotons, or one thousand tons of TNT, while thermonuclear bombs are generally measured in megatons, or one million tons of TNT.