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Helium-3 (3 He [1] [2] see also helion) is a light, stable isotope of helium with two protons and one neutron. (In contrast, the most common isotope, helium-4, has two protons and two neutrons.) Helium-3 and protium (ordinary hydrogen) are the only stable nuclides with more protons than neutrons. It was discovered in 1939.
In stars, however, 3 He is more abundant, a product of nuclear fusion. Extraplanetary material, such as lunar and asteroid regolith, has traces of 3 He from solar wind bombardment. To become superfluid, 3 He must be cooled to 2.5 millikelvin, ~900 times lower than 4 He (2.17 K).
Similar cooling of helium-3, which has a lower boiling point, can achieve about 0.2 kelvin in a helium-3 refrigerator. Equal mixtures of liquid 3 He and 4 He below 0.8 K separate into two immiscible phases due to their dissimilarity (they follow different quantum statistics: helium-4 atoms are bosons while helium-3 atoms are fermions). [30]
Helium-3 surface spin echo (HeSE) is an inelastic scattering technique in surface science that has been used to measure microscopic dynamics at well-defined surfaces in ultra-high vacuum. The information available from HeSE complements and extends that available from other inelastic scattering techniques such as neutron spin echo and ...
The term helion is a portmanteau of helium and ion, and in practice refers specifically to the nucleus of the helium-3 isotope, consisting of two protons and one neutron. The nucleus of the other (and far more common) stable isotope of helium, helium-4, consisting of two protons and two neutrons, is called an alpha particle or an alpha for short.
Helium-3 nuclear magnetic resonance (3 He-NMR) is an analytical technique used to identify helium-containing compounds.Because a helium atom, or even two helium atoms, can be encased in fullerene-like cages, the nuclear magnetic resonance spectroscopy of this element can be a sensitive probe for changes of the carbon framework around it.
Finally, the pure 3 He enters the mixing chamber, the coldest area of the device. In the mixing chamber, two phases of the 3 He– 4 He mixture, the concentrated phase (practically 100% 3 He) and the dilute phase (about 6.6% 3 He and 93.4% 4 He), are in equilibrium and separated by a phase boundary
A helium-3 refrigerator is a simple device used in experimental physics for obtaining temperatures down to about 0.2 kelvins.By evaporative cooling of helium-4 (the more common isotope of helium), a 1-K pot liquefies a small amount of helium-3 in a small vessel called a helium-3 pot.