The difference between an nuclear bomb and a hydrogen bomb.
In: Engineering
Starting in 1945, the first nuclear bombs were fission of uranium alone, later ones were fission of plutonium, which came with higher yields.
ALL fission weapons produce fallout basically proportional to their explosive yield. Pure fission weapons are limited in possible yield at about 500 kilotons, because the weapon will disassemble itself before using more fuel.
Hydrogen bomb (aka “H-bomb”, “thermonuclear bomb”) was first detonated in 1952. These start with nuclear fission, but use the energy to spark fusion in hydrogen fuel. The fusion energy itself is not very significant part of the yield- the real purpose it to generate more neutrons to cause *more fission in the fission fuel* than a pure fission device.
As such, H-bombs are not “cleaner”. Since only a small amount of the bomb is clean fusion, there is basically the same amount of dirty fission fallout per kiloton of yield. You might think “well in a campfire, a hotter flame makes a cleaner burn of fuel”, but it is nothing like that. Any portion of “unburned” uranium fuel that fails to undergo fission is basically nothing to worry about. A greater yield does not in any way “burn up” the fallout it is making.
The one exception was the Soviet’s Tsar Bomba, a political stunt where they built by far the largest bomb ever, 50Mt that was almost pure fusion and produced very little fallout. However, the bomb was comically large, 27,000kg and the size of a small bus. Too large to ever drop on anything.
I’m no nuclear physicist but there is no window for “can you do the same nearly pure fusion weapon in a small 200kg package?” I don’t think you can.
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