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View Full Version : What caused "Hiroshima shadows" ?



small axe
02-16-2009, 05:52 AM
Okay, perhaps we've all seen photos of the "shadows" of people or bicycles preserved in walls etc by the intensity of the A-Bomb blast at Hiroshima.

But I read two different explanations of the cause.

One claims that it was the intense LIGHT that literally burnt the shadows into the surfaces behind the person (and the person was disintegrated) ...

The other suggests it was HEAT that simply scorched the surfaces, "branding" the unshadowed surfaces.

Am I incorrect or not to understand these as being DIFFERENT explanations?

I have a scene where a man is imprisoned in a pitch black dungeon cell. he is visited by what he things is his hallucination of "another prisoner" ...

When the dark cell is opened and light pours in, we realize that even in his black cell ... something (the person he has been talking to) has burnt "hiroshima shadows" of the protagonist into his cell walls.

My dilemma is: if it is HEAT that caused the actual Hiroshima, Japan shadows, then my protag will have been cooked to death ... whereas if it is just some sort of LIGHT (or in my story's case, some spooky alien radiation) then he can have been vsited without necessarily cooking him to death!

So ... anyone have a firm knowledge of what caused the actual Hiroshima shadows to appear in surfaces etc? Heat, or Light (or some other cause)?

Like I said, I read conflicting (I think) accounts of their cause! Any help would be appreciated!

ChaosTitan
02-16-2009, 05:58 AM
Popping this up to Science Fact.

Vincent
02-16-2009, 06:17 AM
The LIGHT brought with it the HEAT. Actually it's a bit more complicated than that, different types of radiation are involved, but yeah, it scorches the unshadowed surface, thus making the shielded patches stand out. The unshadowed area can be either charred, causing a light shadow on a black background, or bleached, causing a dark shadow on a white background. Either way, whatever burnt the surface so bad that a person's shadow was left there, burnt that poor person just as bad.

Pthom
02-16-2009, 06:23 AM
The sort of heat necessary to do that kind of damage IS light--in the form of infrared radiation. Beezle is correct, though, in saying that infrared radiation wasn't the only contributor to the shadows.

small axe
02-16-2009, 09:31 AM
grrrr. rats. But thanks for the info.

CACTUSWENDY
02-16-2009, 09:57 AM
I sure do like your questions. Very interesting.

Nivarion
02-16-2009, 10:49 PM
what i have always wondered about these is, if it was caused by heat then it should have been burning the surface. So why did it make shadows? shoudn't it have made sillouets (maimed word... uh reverse shadows)

Lhun
02-16-2009, 11:10 PM
Another possible explanation is the heat blastwave, i.e. the wave of extremely hot air caused by the bomb, as opposed to direct radiation.
I can think of two sub scenarios for this, a) as before, the people shielded the walls and left a visible shadow, or b) the shadows are the remains of people hit the blastwave.
For both of these they'd have to stand really close to the walls though, to leave recognizable silhouettes. It should be pretty easy to tell from the way the walls look what happened though.

benbradley
02-16-2009, 11:59 PM
The LIGHT brought with it the HEAT. Actually it's a bit more complicated than that, different types of radiation are involved, but yeah, it scorches the unshadowed surface, thus making the shielded patches stand out. The unshadowed area can be either charred, causing a light shadow on a black background, or bleached, causing a dark shadow on a white background. Either way, whatever burnt the surface so bad that a person's shadow was left there, burnt that poor person just as bad.
It might even be left at a similar shade, but with a changed color, similar to white paper or other things that go yellow or fade after months of sunlight exposure.

To expand on the "different types of radiation" thing, a nuclear bomb puts out a large spectrum of electromagnetic radiation, much like the Sun - going from infrared (radiated heat) through visible light to ultraviolet and x-rays. Also, from the higher temperature of a nuclear explosion (millions of degrees vs. about 3,000 degrees for the surface of the Sun) and the shorter distance (1,000 ft or maybe a mile or two, vs. the Sun shining through all the air in the atmosphere, which absorbs a lot of UV), a nuke no doubt puts out a LOT more ultraviolet and especially x-rays than the Sun. I won't make a guess at what band of radiation contributes the most, but I suppose the visible light and ultraviolet from a nearby nuclear blast could make a surface fade as much as years of being exposed to daily sunlight.

Nivarion
02-17-2009, 08:44 AM
It might even be left at a similar shade, but with a changed color, similar to white paper or other things that go yellow or fade after months of sunlight exposure.

To expand on the "different types of radiation" thing, a nuclear bomb puts out a large spectrum of electromagnetic radiation, much like the Sun - going from infrared (radiated heat) through visible light to ultraviolet and x-rays. Also, from the higher temperature of a nuclear explosion (millions of degrees vs. about 3,000 degrees for the surface of the Sun) and the shorter distance (1,000 ft or maybe a mile or two, vs. the Sun shining through all the air in the atmosphere, which absorbs a lot of UV), a nuke no doubt puts out a LOT more ultraviolet and especially x-rays than the Sun. I won't make a guess at what band of radiation contributes the most, but I suppose the visible light and ultraviolet from a nearby nuclear blast could make a surface fade as much as years of being exposed to daily sunlight.

ah that makes sense. i was thinking like if you put your hand on a wall and spray painted over it.

so its more like if your spraying bleach over it instead of color, it would leave the spot where your hand was much darker and it would look like a shadow.