How do they differ in their material makeup, efficiency, scope, scale and destructive power?
In: Chemistry
Nuclear bomb is a catch-all term for two types of weapons, fission-type bombs and fusion-type bombs. Atomic bomb is also a catch-all term, but because the fission-type bombs came first, “atomic bomb” often in context refers specifically to fission bombs. Fusion bombs use hydrogen, and are called “hydrogen bombs” or “thermonuclear bombs.” Whether they are fission or fusion bombs, their explosive output is usually described in kilotons, meaning, the equivalent of a certain number of thousands of tons of TNT.
At the level of atoms, you can generate a huge amount of energy — either in a bomb, or in a controlled form in a power plant — both by splitting atoms apart as well as fusing them together. To split them apart (“fission”), it’s best to start with very heavy elements that have large nuclei, like uranium or plutonium. These are the type of bombs that were dropped at the end of the Second World War. The bombs dropped on Japan had a yield of about 15-20 kilotons, but the largest fission bombs could be up to several hundred kilotons (so several hundred thousand tons of TNT).
Hydrogen bombs or thermonuclear bombs ultimately rely on the energy released by fusing atoms together. To do this, it’s easiest to start at the other end of the periodic table, with very light atoms — hydrogen (hence, the name “hydrogen bombs”). The story then gets a bit complicated, because you have to apply an incredible amount of energy to fuse the atoms together in the first place, *before* you get to the even bigger release caused by that fusion. So, typically, a “hydrogen bomb” actually has a first-stage fission bomb inside it, which produces the energy necessary to trigger the second stage, which is where the hydrogen fusion comes in. These weapons are far more powerful than the fission-only bombs. The largest ever detonated was the Soviet “tsar bomb” test, which was 50 megatons (50 million tons of TNT).
Although you can build hydrogen bombs as big as you could possibly want to, the nuclear yields have not continued to grow. This is because there really are no militarily useful targets massive enough that you would really need a multi-megaton bomb to destroy it. Once the accuracy of rocket targeting was good enough that both sides were confident they could actually hit the targets they wanted to hit, they stopped increasing the yield. Even so, a modern nuclear weapon with “only,” say, 100 kilotons yield is still several times as powerful as the bombs dropped in 1945.
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