He3

Helium-3 (He-3) is a stable isotope of helium with two protons and one neutron. It is the lighter and rarer of the two stable helium isotopes, the other being helium-4. He-3 is non-radioactive and has a nuclear spin of 1/2, which gives it useful magnetic properties for specialized scientific applications. Its magnetic moment is distinct from that of He-4, enabling certain quantum and imaging experiments.

Occurrence and production

On Earth, He-3 is present only in trace amounts and is difficult to obtain in large quantities. It is found in natural gas and in trace amounts in atmospheric helium. He-3 is continually produced in small quantities through the decay of tritium (T) and through cosmic ray spallation, and it is also studied as a potential fuel source for future technologies. Much of the commercially available He-3 has historically been recovered as a byproduct of other processes or is sourced from specialized gas deposits. He-3 is much more abundant on the Moon and in the solar wind, where it is implanted in lunar soil, leading to long-standing interest in lunar mining as a future supply.

Applications

He-3 has several notable uses. In cryogenics, mixtures of He-3 and He-4 enable dilution refrigeration that can reach temperatures well below a kelvin, aiding fundamental low-temperature physics research. In neutron detection, He-3 gas-filled proportional counters are highly efficient and widely used in security and scientific instruments. He-3 gas is also used in polarized form for nuclear magnetic resonance and medical imaging research, including lung imaging. In fusion research, reactions involving He-3, such as D–He-3 fusion, are of interest due to potential aneutronic energy release, though practical reactors remain speculative.

Safety

As an inert gas, He-3 poses minimal chemical hazard but can be an asphyxiation risk in enclosed spaces and presents cryogenic hazards at very low temperatures.