While watching a show about Fort Knox, I began to wonder what movie makers use to fake a gold bar. Is it highly polished brass that the actors just pretend is heavy? Or do they use some kind of paint on lead ingots so that it really is heavy? I remember one shot in Kellys Heroes where they forgot to put any weight in the crates of “gold” and an actor accidentally knocks one aside quite easily while cheering. But that was a crate, not a “Gold” bar.
The eponomous Maltese Falcon prop was made of lead so that it would be heavy. (There were aparently also resin ones.)
There’s always gold leaf, which can be applied to many types of surfaces.
Spray paint.
Although to be perfectly pedantic the item in the film was not the “eponymous” falcon since it was a fake.
They use plutonium (but they have to hollow them so they are not too heavy)
No, that’s only for faking Uranium.
It’s worth noting that even lead is only a little over half the weight of gold, so if you want a truly accurate portrayal, the actors would still need to act like it’s heavier than it really is. But since so few folks realize just how heavy gold really is, few moviemakers care about that level of accuracy.
Plutonium, meanwhile, is only slightly heavier than gold (19.8 compared to 19.3), and uranium is a little less. Even the densest element on the periodic table, osmium, is 22.6, or only 17% more than gold.
That explains the newsreel footage of a bank or federal reserve employee straining somewhat hard to push a cart carrying only about a dozen gold bars.
Yes, exactly. The other day we were watching an episode of *Rome *from season 1, and for all the details they get RIGHT, they still had people flinging around large bars of gold like it was nothin’. (The bars were much larger than Hershey’s bars, though thinner than traditional Hollywood gold bars - maybe 4"X9"X1") And a HUGE cart holding the entire treasury of Rome, in those gold bars and coins in chests, being pulled by two oxen. I just don’t see it happening, folks. Even if oxen are strong, how strong is the axle on a wooden cart?
Sorry to continue hijacking the thread but, when they talk about the density of Uranium, what exactly are they referring to? Is there such thing as pure Uranium for it to make sense talking about its density?
Of course. Why wouldn’t there be?
What units are those densities in? g/cm[sup]3[/sup] ?
oh, I don’t know. I am ignorant of these things. I was thinking of decay, for one. And critical mass. I know that the stuff in reactors is far from pure. And all the talk about reprocessing sounds so hard that I just assumed you never had 100% pure Uranium.
Yes. The SI definition of density is kilograms per cubic metre, effectively the same as grams per cubic centimetre. There was a time when water was considered the (heh) gold standard, with one cc of water by definition having a mass of one gram. This has been replaced with a more strictly-controlled standard, the international prototype, but in practice, a density value is proportional to water (at 4[sup]o[/sup]), hence gold is 19.3 times denser than water. You’d need highly-accurate instruments to determine otherwise.
Anyhoo, I recall gold’s weight being a key element in an Encyclopedia Brown story, in which a swindler hefted, with one hand, a large brick of what he claimed was gold.
I think that critical mass is important for uranium with extremely high concentrations of U235 and for plutonium. Those are the only two substances I know of that have reasonably long half-lives and also fission with both fast and slow neutrons. Thus, from a practical point of view, they are the only two substances that would start chain-reacting in a normal environment.
Uranium in normal concentration is over 99% U238, a relatively stable isotope with a half-life of 4.5 billion years. U235 itself has a half-life of 700 million years.
Plutonium has a half-life of about 22,000 years.
(Note: thorium is called a fissile element, but it does not itself split. Instead, neutron bombardment converts it to U233, which does fission).
Both uranium and plutonium will oxidize. I’m not sure how many oxidation states they have, but as I remember plutonium has something like 5? They also both react with a variety of other compounds.
So, uranium and plutonium can be made as pure as most other things in the universe. They both have several isotopes, decay into other elements, and react to form compounds. Even so, these processes are relatively slow and controllable.
That’s for getting particular isotopes of uranium (typically U235). But if you don’t care about which isotope is which, you can easily refine pure uranium, which would mostly be the less useful U238.
Heck, what’s a factor of 1000 between friends? I still say that instead of the centimeter-gram-second system or the meter-kilogram-second system, we should use the meter-ton-second system. That way, none of the base units has a prefix on it, and you still get to keep the density of water as 1.
Right – and for a lot of real-life applications, you would need to deal in microtons. Imagine having recipes with, e.g., 100 microtons of flour.
Well, Uranium doesn’t generally exist in nature in pure form, but is typically refined from “Uraninite” (largely UO[sub]2[/sub] and other compounds), historically known as “pitchblende”, but once you have a solid chunk of Uranium, I figure you could hold onto it for a year (or even a hundred years) and lose virtually none of it.
Uranium, most of which is the isotope U-238, “burns” so slowly, in fact, that is makes for poor fuel, so the main focus is to trim away most of the calm bucolic mostly-harmless U-238 and get at the relatively useful, happenin’, dancin’-like-a-fool 0.72% that is U-235. When people speak of “reactor-grade” and “weapons-grade”, they mean uranium that has been “enriched”, i.e. most of the U-238 has been trimmed away, leaving a smaller total mass but with a higher percentage of U-235.
If you start with, say, 1000 kg of refined Uranium (i.e. everything that is not Uranium has been removed), you have 7.2 kg of U-235. Combine it with hexafluoride, making the gaseous UF[sup]6[/sup]and feed it through a gas centrifuge for a few years to trim away the U-238. Remove 97% of the U-238, leaving 35kg of material, of which 20% is U-235, meeting the definition of Highly Enriched (HEU). Although Low-Enriched (LEU) is suitable for some reactor designs (hence reactor-grade), HEU is the minimum required for weapons (hence 20% minimum for weapons-grade though getting 90% U-235 would be ideal). Along the way, you start creeping into critical mass territory, when it’s no longer necessary to start a chain reaction artificially. For pure U-235, this is about 52 kg. U238 will never go critical on its own (and its presence will dampen U-235’s reaction, meaning a 20% U-235 mass won’t go critical unless you get at least 400 kg of it - if this happens, duck). A nation that is seeking to enrich Uranium beyond 20% can try to claim it isn’t for weapons, but that’s GD territory.
Heh, well, that would have worked if I’d said it correctly. Grams per cc is equivalent to tonnes per m[sup]3[/sup], not kg per m[sup]3[/sup].
I seem to recall an article on gold which had the reporter visiting a vault, and seeing the bars of gold. His guide told him he could have one, but he had to pick it up one handed from above.
He couldn’t (of course). I doubt that even a “worlds strongest man” contestant could get enough purchase to lift the bar.
But I’d try.
Si