I visited the Hiroshima museum last year. They've got a set of stone steps, a person was sat there when the bomb went off and they were simply vaporised. The stone steps bear the residue of the person, almost like a shadow.
The atomic bombs weren't close enough to vaporize anyone since they were detonated in the air, what you see is disintegration which is a little bit different and instead of turning the human body into what could be considered "nothing" the materials are torn apart and get embedded into the surrounding environment. Some vaporization did occur, but only on plants and the skin tissue of humans.
Are you sure that's the explanation?
It could be (and I think it's more likely) that the rest of the stone was lightened, and the part in the shadow, wasn't.
No "residue of a person", just literally "shadow".
See also: https://en.wikipedia.org/wiki/Human_Shadow_Etched_in_Stone
At that distance you wouldn't be vaporized, but burned. What you see on the steps is not vapor deposits, but rather they are shadows.
The immense heat and light from the detonation burned/discolored the stones, but not in the shadow of the person sitting on the steps. Hence why you can see these 'permanent shadows' in various places in the city. Some caused by humans, but most are just shadows of structures. For example bridge railings: https://www.atomicarchive.com/media/photographs/hiroshima/im...
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Visited Hiroshima over a decade ago during a school trip, and had a local guide that was a survivor. Very powerful.
As a teenager we also visited concentration camps on a school trip, and a survivor joined the trip from Norway to Germany. We got to know him a bit during the week long trip, and there was a session where he told his story. I'll never forget this, and I think it affects me to this day.
Soon we will have no Time Witnesses left.
Edit: I remembered a very specific anecdote he told, about how him randomly having learned to knit helped when in a concentration camp, as some officer wanted something to be made, and he then could sit inside and do that instead of working himself to death in the quarry. Based on this I managed to find his name again now.
Haakon Sørbye, thanks for telling us your story.