Yaver_Mbizi t1_iwcnub0 wrote
Reply to comment by mfb- in Why do neutrons tend to interact more readily with light nuclei rather than heavy ones (i.e., why is water a better neutron shield than lead)? by Calgaris_Rex
Sorry for taking so long to reply - I first wanted to get the numbers right and then kinda forgot about this comment.
> Does that need any special purification effort?
Yes. Specifically something called "superleak" or "superfluid helium filter" is used. It's basically a filter with material so tightly compressed that only a superfluid can go between the particles. As helium-3 reaches superfluidity at a much lower temperature level than helium-4, the isotopes can be thusly separated.
>Helium-3 is already a tiny fraction of the helium we extract.
Yep, but the less of it, the better. The natural content is about 10^(-6), whereas by using a superleak you can get something around 10^(-11), which is much better.
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