"Taken from the reactor that Hitler tried to build. Gift of Ninninger.”

May 1, 2019 11:13 AM

Tracking the journey of a uranium cube - how did a cube of uranium from a prototype WW2 reactor end up in a lab in Maryland?
Physicists Timothy Koeth and Miriam Hiebert in Physics Today.
posted by thatwhichfalls (8 comments total)

Nice story. But no mention of how dangerous handling a cube of raw uranium is. I assume the soldiers who dug up the buried cubes had of radiation exposure of some significance?
posted by jetsetsc at 11:41 AM on May 1, 2019 [1 favorite]

Wow, so many tantalizing details in there! E.g.: "Heisenberg had escaped earlier by absconding east on a bicycle under cover of night with uranium cubes in his backpack."
posted by LobsterMitten at 11:51 AM on May 1, 2019 [2 favorites]

So now we know where the Tesseract was between the time the Red Skull disappeared and Mar-Vell built the lightspeed drive.
posted by ejs at 11:58 AM on May 1, 2019 [10 favorites]

If I recall from _The Curve of Binding Energy_, raw uranium metal isn't dangerous to handle, and apparently Harvard hands their cube around to students. I'd wonder about any dust that might happen from people handling and dropping it.
posted by tavella at 12:02 PM on May 1, 2019

The block is not particularly dangerous. Koeth gave a talk here this last semester on this topic and passed one of the blocks of uranium around the audience. They weigh a surprising amount for their size (but then again, so does lead and gold), but natural uranium isn't exceptionally dangerous if it isn't in the form of dust that you could inhale. The half life is very long (4.46 billion years): which means it won't stop being radioactive any time soon, but also means the actual rate of radiation being emitted is low. The very dangerous radionucleotides are the ones with relatively short half-lives, as they are dumping their radiation out into the environment quickly (but those also decay away quickly). Granted, some of the uranium daughter nuclei have short half-lives, but since the parent lifetime is so long, there isn't much of the daughters around at any time.

If the uranium block in question had been in a reactor, the neutron flux could have created some of these short-lived fission products, but the block in question never was in a working reactor and so it's not much more dangerous than the uranium-doped glass that used to be all the rage before other uses for uranium were discovered. I have a beer stein from the Czech Republic that is uranium doped, and I worked out that I get about the same radiation dosage from the potassium in the beer I drink from it as I do from the glass itself.

Uranium emits mostly alpha particles, which are efficiently blocked by the dead cells on the surface of your skin. It also emits gamma rays which are penetrating, but those also do less damage. The danger from uranium's radiation is if it gets blown into the atmosphere and then absorbed into your lungs. It can then be incorporated into your body, where the alpha radiation can damage cells at short range. This is a risk in war zones where the US has used significant amounts of depleted uranium rounds, and uranium will spark and get into the air. It is also a heavy metal, and toxic, so getting into your system is chemically bad for you in addition to being radioactive.

I wouldn't advocate letting your kids play with pure uranium for any length of time (and definitely wash your hands after you handle it), but that's more to do with the fact that it's a heavy metal than the radioactivity. I wouldn't let them play with lead blocks either. I have held uranium in my hand without any qualms.
posted by physicsmatt at 12:15 PM on May 1, 2019 [20 favorites]

I found this explanation on Stack Exchange, which includes math I don’t understand but makes me feel better knowing someone else does.
posted by Big Al 8000 at 12:23 PM on May 1, 2019

@physicsmatt I know Tim, and he’s a fun guy. We were at FNAL at the same time. The University of Chicago and University of Tennessee Knoxville uranium slugs that get passed around in class are clad in an aluminum sleeve to prevent contamination from dust (I’ve held both in my hand). Nearly undetectable alphas on the outside of the auminum sleeve, though there was minimal neutron flux and some gamma radiation off the outside of the sleeve of the Chicago one. If I recall correctly Univ of Michigan also has one clad in aluminum for demo, but it’s been a while. I would assume the Harvard cube is in a Lexan cylinder for display or other means similar to the picture in Tim’s article. Perhaps a Harvard physics or other major can comment. It’s always a popular thing to demo in undergrad labs and lectures.

Great job to Tim on the front cover of Physics Today.
posted by cyclotronboy at 2:18 PM on May 1, 2019

This sent me down a very educational rabbit-hole this morning, finding out if you can drink heavy water (it's not radioactive, but you shouldn't drink it), if you can knock a proton off something, e.g. to turn mercury into gold (not really, although maybe you could possibly do photodisintegration with a laser), can you add a proton to something e.g. to turn platinum into gold (Yes, in 1919 Rutherford demoed turning nitrogen into oxygen by irradiating it but it's hard and anyway platinum is worth more than gold.). So there goes my brief career in alchemy.
posted by w0mbat at 3:16 PM on May 1, 2019 [4 favorites]