Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I was looking at old photographs of the nuclear tests on the bikini atoll. It dawned on me that you don't want to run film through airport x-rays, as it exposes the film. I've been told that a nuclear explosion emits all energy on the spectrum (IR to Gamma). If this includes x-rays, why wasn't the film ruined? Is it because:

1) I'm an amateur radio operator. One of the things I'm familiar with is that RF signal strength starts at a point, and changes by a sum of squares (correct me if I'm wrong PLEASE!) as you move away from the point. If all energy behaves similarly in this respect, is this just a, "not enough x-rays at this distance to effect the film discernibly?"

2) The body of the camera must be taken into account (maybe?). Most cameras of this time period were metal (I believe). Most of the film curtains/iris' we're made of metal too. The only point of entry might have been during exposure?

3) A combination of 1+2

4) Some other awesome physics thing that I can't wait to learn about?

5) Pics of nuclear blasts are all photoshopped productions (I'm kidding of course)?

share|cite|improve this question
    
I think it's worth pointing out that people didn't use particularly ordinary cameras for a lot of these photos, and very likely not ordinary emulsions either. Certainly photos taken early in the explosion were taken with very short exposures indeed (there's a reason it always looks dark). – tfb Mar 19 at 9:23
    
Link seems not to point to the bikini atoll. – Qmechanic Mar 20 at 14:06
up vote 5 down vote accepted

I believe most of the em-spectrum from a nuke is low energy. So when you take a photo you get a lot of visible light and heat, and only small amounts of high energy radiation on your film. Also the lens might be transparent to visible light, but non transparent to high-energy em-waves.

Edit: just found http://www.fas.org/nuke/intro/nuke/thermal.htm

It says that most of the inital photons are indeed in the X-ray spectrum, but these high energy photons are quickly absorbed by the atmosphere. So the spectrum reaching the photographer is determined by the atmosphere transparency.

share|cite|improve this answer
    
If it matters, the tests I'm referring to were conducted by JTF-7. They were high yield (I believe high energy) studies. – Everett Jul 28 '12 at 15:42
3  
Yes, the atmosphere absorbs X-rays fairly well; that's why we put X-ray telescopes in orbit. – Keith Thompson Jul 28 '12 at 20:38

The pictures were taken from miles away. High energy photons don't make it very far through air before they are absorbed. In fact, that's what makes the blast: The gamma rays heat a large volume of air to white heat, and the sudden expansion of the air creates the blast wave.

share|cite|improve this answer

One possibility to consider: Many of these photographs were taken long enough AFTER the explosion that much of the energy of the explosion has gone into stirring up debris rather than the initial flash. If only the initial flash was photographed, there would be a bright spot at the location of the bomb, and almost no disturbance yet further away.

share|cite|improve this answer
1  
However pictures taken very early do exist: in fact I think they were important parts of the tests (for instance this is Trinity at 0.016s, and there may be earlier ones). – tfb Mar 19 at 9:24
    
Earlier Trinity images: the first image here seems to be 0.1ms. – tfb Mar 19 at 9:31

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.