last night I was watching a movie “The fourth protocol” is which the bad russians (it dates from 1988, now of course it would be bad arabs) assembled a small atomic bomb by hand. They handled the U235 core, about the size of a basketball without gloves etc for several minutes. Now could you do that without getting very severe radiation burns?
You would get burned but not right away. If I recall corectly the core has to be machined to a high degree of precission. It would seem that handleing it would mar the surface. Possibly beond use.
Not true. First, only the core of an “implosion” device has to be machined well, and the metal is hard enough that you aren’t going to scratch it with your bare hands. As I recall, the movie involves a “gun” type device, which is much less sensitive to configuration differences than is an “implosion” device. More on this later.
As to the “burns”, this is also not correct. Subcritical masses of [sup]235[/sup]U or [sup]239[/sup]Pu are
[ul][li] not particularly radioactive, with halflives of 24000 years for [sup]239[/sup]Pu and about 700 million years for [sup]235[/sup]U.[/li][li]not dangerously radioactive, i.e. the major emission component of these elements are a particles which are nearly harmless when they are not inside your body. Specifically, if you don’t eat or inhale an a-emitter your skin’s outer dead layer will stop most of the radiation, but even a thin layer of cotton will protect you from even that in most cases.[/li][/ul]
As I recall, and please correct me if I’m wrong, Pierce Brosnan is assembling a “gun” type bomb, where he has two chunks of material that are both sub critical, and there is a tense moment when he’s assembling it that he almost drops part A into part B, and he sweats a lot and the dramatic music swells to a crescendo.
My point being that gun type bombs consist of two sub-critical masses, each of which when handled individually would be quite harmless. If the two pieces are put together, depending on the design of the device they may be close to critical or even supercritical, in which case Pierce might as well hang around to watch the fireworks, because he’s going to get a rather serious dose of neutrons.
This is because while the most common mode of decay for [sup]235[/sup]U and [sup]239[/sup]Pu is a emission, when a critical mass is assembled the dominant form of decay becomes spontaneous fission with lots of neutron emission. This is what makes the bomb go boom, but neutrons are about a gazillion times more harmful than a particles, are difficult to shield, and if you get a bunch of them you’re toast.
For an extreme example of what might have happened to Pierce if he’d dropped the two pieces together, see http://www.fas.org/nuke/trinity/accident/critical.htm#cr082145
Excerpt:
Note Pierce could probably have still carried out his mission, but he may have reduced the yield of the device by allowing it to slowly go critical for a moment before he assembled it, and he would have had radiation poisoning and thus may not have enjoyed his vacation as much.
Radioactive uranium with low CPM in small quantities is safe to handle. Check out www.unitednuclear.com for 100,000 CPM uranium chunks you can buy.
Gosh I sure hope so… 'cause people have been saying I have this certain glow about me lately and I’m beginning to wonder if it isn’t literal. :eek:
No. Read Ricard Rhodes’ book Th Making of the Atomic Bomb. Wen they signed for the first delivery of a Plutonium core from Oak Ridge, th fellow in charge (I forget who – Not Oppenheimer, I think) took it out and held it in his hand. It felt very dferent than he’d expeced – although it looked like shiny new metal., it idn’t feel cool. It felt warm and “alive”, because of the nuclear disintegrations taking place. There was a constant flow of heat, particles, and (one assumes) gamma rays, but all at a pretty low level.
Me, d be afraid of abrading bits of highly toxic plutonium, but you know me. I assume sub-critical masses of uranium would fee the same.
I was quite surprised when shown a HS physics video of Uranium extraction and there was a guy openly handly the uranium in the stage after it had been refined from yellowcake, It looked a lot like sand and he was just running his fingers through it.
probably the same guy who used to drink agent orange in Vietnam to show the troops how safe it was.
Just wash your hands when you are done, and you’re fine.
My grandfather had a slug of uranium about the size of a silver dollar, but twice as thick. It was really heavy, and a matte black. Didn’t feel warm, but U is much less active than Pu. He used to take it out of its place in his knick-knack shelves and let us kids handle it.
He also gave me a chunk of pitchblende (uranium ore) about the size of a tennis ball with a flake of gold in it. I kept it in my rock collection. When I was about 11 I got freaked out about radiation and put it out in the toolshed. When I was about 16 or 17 I learned about the different types of radiation, and brought it back into my box. It’s sitting in my linen closet now.
Anyway, while some might say “That explains a lot,” it’s really quite harmless as long as it is far from a critical mass, or if it is not the type of Uranium that goes critical.
This incident was recreated (and significantly embellished) in the (rather lousy) movie “Fat Man and Little Boy”. Actually though, it was probably the best scene in it.
The bomb in “The Fourth Protocol” wasn’t a true ‘gun’ type like the one used at Hiroshima. That one (Little Boy) had two equal hemispheres of uranium fired together at high speed.
In TFP the core consisted of a baseball sized sphere with a cylinder shaped section removed (like an apple core). Alone both pieces were sub-critical. When combined they could start a chain reaction. There was also a disk shaped ‘accelerator’ which the core would hit after it slid into the hollowed-out sphere. It emitted neutrons and helped boost the reaction.
If you remember the plot he was going to detonate it at a US army base in the UK so it would look like an American nuke had gone off by accident, hopefully causing the Brits to expel the US from their soil. Because of this, the spy’s bomb was a very crude, dirty, low-yield device.
Okay, I know that the definition of critical mass is the mass needed to sustain a chain reaction…but there’s got to be more to it than that.
Why does mass matter?
When we were kids my brother and I recieved a microscope. It had several viles of different substances to look at. One of the viles contained Uranium ore.
It was probably Calmeachams notopperheimer guy that was trying his hand at entrepreneurship.
Because if the mass islower than the critical mass, each reaction would cause >0.99 reactions and the whole thing would peter out. If it passes the critical mass, each reaction causes <1.001 more reactions and you get exponential growth. Eg. if each reaction casued 2 more reactions, it would go 1, 2, 4, 8, 16, 32, 64… after 30 steps, you would be up to a billion reactions per step.
Mass matters because the neutrons which cause the chain reaction have to be captured before they escape. In a small sample they simply go straight through the uranium, only when the mass or size is big enogh do they get stopped.
Somewhat off topic (or maybe not), but it is not unheard of for Model Railroaders (a handful at most) in the smaller scales to weigh their model locomotives using depleted Uranium. This is because (simplified) more weight = better traction and hence better operation; most modellers use lead because of it’s heavy density, so uranium is even better in that department
couldn’t find anything specifically on U-235. But on depleted uranium
from www.vbs.admin.ch/ls/e/bg_info/du/du_study_print.pdf
DU outside the body acts exclusively via the emitted gamma and beta radiation, since the alpha radiation is
absorbed by the outermost layers of the skin and therefore does not affect the living tissue. The dose-rate in
the vicinity of DU is very low. One kg DU at a distance of 1 meter produces a dose of less than 1 mSv per
year. If a DU surface is touched by the bare skin, a localized dermal dose of about 2 mSv per hour results
(Rostker 2000).
a msV is a pretty low dose, X-ray type value.
Now depleted uranium is about 10 x more radioactive than U235 as that site informs me. So I guess old Pierce was safe when he handled the U235 metal. Damn - I thought I had found a hole in the movie
The critical mass is simply the quantity of uranium that must be in the same place for the number of neutrons that do not escape from the mass to be high enough to continue the chain reaction.
As for handling, it was my understanding that plutonium (though not uranium) was mildly toxic just as a chemical element, ignoring the fact of its radioactivity.