Hiroshima and Nagasaki didn’t, but other detonations did, like Castle Bravo.
In: Chemistry
Most nuclear bombs are designed to be air burst because the blast, radiation, and heat come from a point hundreds of meters in the air, which means the overall radius of the effects is much larger. Think of like shining a flashlight on a wall from close to it, or from across the room. But the fireball, that sphere where everything within it is vaporized, never touches the ground.
A ground burst causes a crater because about half of the effects are directly on the ground and the fireball vaporizes a big chunk of dirt.
Take for example, Little Boy dropped on Hiroshima, detonated at 600 meters. Its fireball was 180 meters, so that never touched the ground. Here are some other attributes:
* Heavy blast damage (everything leveled): 340 m
* Fatal radiation: 1,200 m
* Moderate blast damage (non-concrete buildings gone, fires rage): 1,670 m
* Thermal radiation radius (3d degree burns): 1,910 m
* Light blast damage (windows break): 4,520 m
But let’s say they detonated this on the ground. First, the fireball a couple hundred meters across will have vaporized a lot of dirt, and there would be severe radioactive fallout. Then,
* Heavy blast damage: 540 m
* Fatal radiation: 1,340 m
* Moderate blast damage: 1,130 m
* Thermal radiation radius: 1,680 m
* Light blast damage: 2,900 m
So you see the heavy blast and fatal radiation radii are higher, the bomb is 600 meters closer to the ground targets. But the overall radius of damage is much smaller. So obviously we only want ground burst against small, very hardened targets, and where we don’t care about fallout.
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