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It's the smallest monatomic gas, so it can wriggle through even the tiniest of holes. Normally you'd liquify a gas to store it, but helium doesn't liquify unti
by astrodust 8y ago
It's the smallest monatomic gas, so it can wriggle through even the tiniest of holes.
Normally you'd liquify a gas to store it, but helium doesn't liquify until you crank it down to 4°K, which is really, really cold. Liquid oxygen and nitrogen have significantly higher boiling points.
Now if you do liquify it, the real fun is it's a superfluid so it's going to crawl all over the inside of the container, it won't just stay at the bottom.
So if you don't keep it at 4°K, or -270°C, it's going to boil, and if it boils it's a gas, and if it's a gas it's going to find any opening to squeeze out of.
- jeffwass 8y ago>Now if you do liquify it, the real fun is it's a superfluid so it's going to crawl all over the inside of the container, it won't just stay at the bottom. Not true. LHe’s boiling point (at atmospheric pressure) is 4.2K. The lambda point when it becomes a superfluid is 2.2K. So there’s a decent temperature range when it behaves as a normal liquid.
- marmaduke 8y agoGood clarification. I’ve regularly seen helium refills of an MEG scanner and apart from being cold it didn’t look particularly troublesome.
- astrodust 8y agoGood point but it also means that if you can keep it precisely in the 2.2K to 4.2K range then nothing strange happens. That's a pretty narrow band to operate in.
- jeffwass 8y agoIt’s a wider range than you think. Temperatures work logarithmically. The lambda point occurs at roughly half the absolute temperature of the boiling point. For comparison room temp is roughly 300K, and half of that is 150K or minus 120°C. Would you call the temperature range between minus 120°C and room temp (call it 20°C) a “narrow band”?