Nuclear Physics 101

[AndyC]

Reading the post on human shields, I got to thinking about screenwriters who assume any metal object will stop a bullet. It made me think about the old assumption that lead has some quality that stops radiation. Truth is, it's just really dense, allowing you to put more shielding between yourself and the radiation with less thickness than if you used, say, aluminum. It's also cheap and easy to work with (even if it is toxic). I know some types of radiation won't even go through clothes, but I'm talking about intense radiation - the stuff that makes bugs grow to enormous size.

Come to think of it, the whole atomic mutation thing is pretty funny too. No disease or random tumors here, just gigantic people and animals, or tiny ones, as the case may be. Better still, one random mutation can create a perfect predator, with claws, fangs, superior abilities. Or it can splice genes if you happen to get bitten by a radioactive spider, perfectly melding the attributes of two completely different creatures.

Anyway, what are your favourite misconceptions (or interesting fictional properties) of atomic radiation.

[rich andrini]

i would have to say the hulk. gettting hit by radiation would either kill u or make feeble and sick beyond belief. the hulk is the the total opposite of that. who knew it could turn u into a giant ass kicking monster.

"Dont be a fool for ur tool"

[Ash]

Weren't the Fantastic 4 given their powers through radiation when they travelled into space?

[rich andrini]

ASHTHECAT wrote:

> Weren't the Fantastic 4 given their powers through radiation
> when they travelled into space?

yup they fall into the same catergory as the hulk and spider man instead of agoinzing death of radiation poison or something like that they become superheroes!

"Dont be a fool for ur tool"

[raj]

And Superman's x-ray vision.  Hello, x-ray radiation emanating from someone's eyes?  Does he have radium or some such thing lodged in his brain?

[Andrew]

You know, "Day the World Ended" did pretty well in this respect.  Some of the animals and humans became mutants, but most died (if memory serves).  They skewed it a little with the animals mutated aboard the test ships that were sketched.

You know what is throwing me off here?  Trying to remember if what my memory is telling me was from the original or from one of the knock-offs.

Also, what is often largely ignored, is that airborne particles are a huge culprit as far as radiation contamination goes.

[AndyC]

The weird thing about x-ray vision is that superman would need a radiation source on the other side of the object he's viewing.

[AndyC]

Andrew wrote:
> Also, what is often largely ignored, is that airborne particles
> are a huge culprit as far as radiation contamination goes.

One of the things that impressed me about The Day After was that it actually showed fallout as a radioactive dust that was settling back to the ground in the days after the blast. Nice scene with Steve Guttenberg and that chick running around outside, kicking up the dust. You can just imagine what it's doing to them.

[Mr. Hockstatter]

I always get a kcik out of how nuclear reactors turn into nuclear bombs if you shove a few sticks of dynamite in there somewhere.  You need to compress the radioactive material to a critical mass in order to get a nuclear explosion.  Just destroying a nuclear reactor would create an explosion, probably when the cooling system blew apart, but there wouldn't be any critical mass achieved, there'd just be a huge amount of radiation released, like Chernobyl.  But no 10 megaton blast.

My favorite example of this would be Ghosts of Mars, where they blow up a nuclear reactor which, of course, makes it into a nuclear bomb.  Not only that, but the characters are only a few kilometers away from the reactor when it blows, and they switch to a view from orbit, and the explosion is the size of Texas.

[ulthar]

Mr. Hockstatter wrote:

> You need to compress the radioactive material to a
> critical mass in order to get a nuclear explosion.  
>

I think you are mixing physical properties, here.  You cannot compress something to create mass.  Compression is related to density, but cannot change mass itself.
The critical mass is there or it is not.

Also, IIRC, the idea of compressing something with an explosive to create a nuclear explosion is related to a fusion device (like the H-bomb), where as critical mass is a fission device concept.

In a fission device, a critical mass *WILL* explode - all it needs to start the process is neutron or two.  Basically, the critical mass is the mass at which there are sufficient neutrons produced to sustain a chain fission reaction, which is initiated by neutron bombardment.

A fusion device, such as the H-bomb, has hydrogen as it's real explosive material, but uses the shock produced from a fission explosion to compress the H2 enough to fuse into helium.  AFAIK, the fusion device has nothing directly to do with critical mass, since it is not neutron cascade that causes the chain reaction (though one would need a critical mass of active material to sustain the fission process).

The early history of the H-bomb engineering was a fascinating and frightening footnote in 20th Century History.  One of the first bombs made produced an explosion that was many, many times larger than the designed thought it would be, which is really scary if you think about it.

[AndyC]

Actually, fission devices do use compression, but what compression does is reduce the critical mass to less than the amount of fissile material. Critical mass, as I understand it, is determined by a ratio of mass to surface area. A small ball of plutonium has a higher ratio of surface area (opportunity for neutrons to escape) to mass (neutrons released). As the ball gets bigger, the ratio changes, and a lower percentage of neutrons escape, with more colliding and causing additional reactions until kaboom. No added neutrons are needed, since the natural radioactive decay of the material is already giving them off. Basically, a big enough piece of plutonium or enriched uranium will blow up all by itself, without any help.

The simple way to reach critical mass is to slam two smaller pieces of fissile material together. The Hiroshima bomb was of this type.

Compression (using shaped charges) works not by increasing mass but by reducing surface area (the ball gets smaller while retaining the same mass), accomplishing the same result. I think it might actually be more efficient though. This was the type used for the Trinity test, and on Nagasaki.



Post Edited (04-28-04 08:50)

[odinn7]

Whew...You guys are giving me a headache...

[Prophet Tenebrae]

Of course - if Bruce Banner/Spider-Man/The Fantastic Four all died horrible deaths instead of gaining super powers, it goes without saying they wouldn't have made as big an impact...

It's the kind of sad inevitability, like main characters never dying...

10

[ulthar]

Fair enough.  I knew they used explosives to slam two smaller pieces together in fission devices, but I was thinking that was to keep the masses apart for 'safer' handling, then jam them together quickly.

"The Fourth Protocol" with Pierce Brosnan and Michael Caine I think gives about as good an overview of building a fission device as in any movie I've seen.

A couple of years ago, I saw a pretty cool Outer Limits episode where a kid discovered, while taking a Physics or Engineering test, a way to make a fusion device more efficient of powerful or something.  He went a little nuts and took the class hostage.

****SPOILER BELOW****


 He ended up getting killed by the 'authorities.'   The show ended with another kid taking a test and discovering the same thing.

[AndyC]

I see what you mean. Not sure how this thread degenerated into intelligent scientific discussion. I was kind of hoping for everybody's favourite crazy fictional properties of radiation, and maybe some examples.



Post Edited (04-28-04 10:04)