Yeah, zarking photons!
All the discussion so far has been about surface energy. I wonder if the energy deposited by penetrating photons would be significant.
Well, I’m sure that there’s some infrared (there’s going to be some of pretty much everything in a nuclear explosion), but you’re probably going to get a heck of a lot more visible-light heat, ultraviolet heat, and even x-ray heat.
A lot of people have this notion that infrared light, specifically, is heat, but actually, all forms of light can equally be heat: It just depends on temperature. We’re used to thinking of infrared as heat because most of the hot objects we’re familiar with (animal bodies, campfires, etc.) are at a temperature that mostly produces infrared. Get hotter, though, and that changes: The peak of the Sun’s thermal emissions, for instance, are in the visible range, and for an arc welder’s arc, it’s in the ultraviolet. Those are heat, too, just as much as the infrared from a body is.
Blast—40–50% of total energy
Thermal radiation—30–50% of total energy
Ionizing radiation—5% of total energy (more in a neutron bomb)
Residual radiation—5–10% of total energy with the mass of the explosion
Nuclear weapons emit large amounts of thermal radiation as visible, infrared, and ultraviolet light, to which the atmosphere is largely transparent. This is known as “Flash”
Even IF there was enough thermal radiation to vaporize a person at those closer ranges, there was probably not enough TIME to do so before the blast wave arrives in short order and does other things.
Yeah, maybe if we refuse to talk or think about morbid topics, they’ll never happen again. George Santayana once said something like that. Except it was the exact opposite.
–Mark
If we’re talking about vaporized in the purest sense that may be true. It’s not like any country is going to release movies of the tests done with animals. The best I can show are wooden structures smoking profusely before the shock wave hits.
Nitpick: it’s 42.6% of that temperature. Give or take.
The SDMB is one of the **best **places to discuss morbid stuff.
Actually, there are a few movies showing the effects of nuclear weapons testing done with animals. I found a few on YouTube just now, without much trouble, including a couple of Soviet and Chinese ones.
And as a matter of fact…hot dang! It looks like “Effects of Nuclear Detonations on a Large Biological Specimen (Swine)” from Operation Plumbbob is declassified and available online, as a PDF.
Neat reading, however I suspect not much help here, as the pigs weren’t being placed into positions where they would be vaporized. Something more along the lines of Nukemap would be more help, as it has the ability to plot out customized blast effect data, including thermal effects, on a map. If someone can figure out how much energy (in calories per square cm) it would take to “vaporize” a human body, the number can be inputted into the web page you’d have the answer almost immediately.
Or, if you want to go old school, the appropriate formulas for determining the same are probably in Glasstone and Dolan’s The Effects of Nuclear Weapons, available online, if you don’t have the hardcopy. (I’ve got the paperback, myself)
There are various ways to calculate this, whether “vaporize” means treating the body as water and flashing it to steam (it’s 70% water), or disassociating all atomic bonds like a Star Trek phaser. Either way it appears the Hiroshima bomb did not remotely have enough energy for either one.
Using heat of vaporization for a human-body-size water vessel, this is 142 mega Joules: Excerpts From The Mad Scientist’s Handbook: So You’re Ready to Vaporize a Human | Scientific American
Total energy output of the Hiroshima bomb was 84 tera Joules. For simplification we will first consider 100% of all energy is converted to heat, not the typical 50/35/15% split between blast, thermal and radiation. If 100% of the available bomb energy converted to heat will not cause vaporization, then the actual device at 35% will clearly not.
At the air burst height of about 1,900 ft this forms a sphere with a surface area of 42162053924 square cm.
The energy flux per unit area at 1,900 feet would be: 84E12 J/42162053924 square cm = 1992 Joules per square cm.
An approx. human body surface area facing the detonation might be about 900 square cm, so total energy delivered would be 1,992 J/square cm * 900 square cm = 1792800 Joules. A Joule is a watt-second, this would be equivalent to 1.79 megawatts on your body for 1 sec.
So 142 mega Joules would be required to vaporize all water in the human body, but the total energy falling on a human body at ground zero under the Hiroshima bomb is “only” 1.8 mega Joules – and that assumes 100% conversion to heat. In actuality heat energy would be about 35% of that.
So it would be worse than a sunburn on planet Mercury, but it apparently would not vaporize the body.
OTOH, if you were standing underneath the 100-ft tall tower holding the “Trinity” bomb near Alamogordo, NM, the energy (at 100% conversion) would be 719,000 Joules per square cm or 647 mega Joules. If we use 35% for the typical heat energy component of a fission bomb, we get 226 mega Joules, which is above the above-mentioned 142 mega Joules required to vaporize all water in the body. This would be consistent with much of the steel tower being vaporized.
I think that answers it pretty comprehensively, thank you Joema and everyone else!
Yep, kudos to joema!
In terms of the Trinity tower, since it was right at the very center of the nuclear explosion isn’t even saying that it melted not really correct? Temperatures there would be in the tens of millions of degrees, so it didn’t just melt or vaporize, the bonds that hold the atomic structure of matter itself break down at that point.
Reason I ask is when I was a kid the film The Andromeda Strain was one of my favorites, mostly for its scientific realism. But at the time my older brother said that the idea that the nuclear self-destruct detonation would merely provide Andromeda with tremendous energy to grow and multiply was silly, for the reason I stated above. It wouldn’t make any difference that it was ‘alien’ life, nuclear physics still meant that any and all matter would break down inside a nuclear explosion.
That’s precisely what happens when metal is vaporized.
Note that it’s the atomic structure that breaks down, not the nuclear structure. Oh, that’ll happen, too, but only for a very small proportion of atoms.
If the nuclear structure of some of the atoms in the tower were to break down, wouldn’t that release even more energy? 
I believe that you use an atomic bomb to fire off a fusion bomb.
But fusion isn’t tearing atoms apart, it is putting them together.
NM. 
The tower was probably made mostly of iron, and anything you do to an iron nucleus will absorb energy, not release it.
Ah - I know about iron collapse in stars. Now I get it. Thanks.
Does Hersey actually say anything of the sort? The Wikipedia page on the book cites a footnote 7 for “people with melted eyeballs, or people vaporized, leaving only their shadows etched onto walls” that points to pages 69 and 96 of an 1973 Knopf edition of the book. Checking against a copy of the 1946 Knopf hardback, p69 (or rather p68) covers the melted eyeballs, but p96 corresponds to this passage in the original New Yorker article:
Which seems rather cautious on the whole matter. There’s no suggestion that people were vapourised or that this left a pile of ashes. (Which somehow survived being blown away by the later blast wave?)
I’m not sure that Hersey ever otherwise expanded on the matter in any later editions of the article/book.
Yeah but it’s such a short exposure it really can’t do much.
