General | |
---|---|
Symbol | 3He |
Names | helium-3, 3He, He-3, tralphium (obsolete) |
Protons (Z) | 2 |
Neutrons (N) | 1 |
Nuclide data | |
Natural abundance | 0.000137% (% He on Earth) 0.001% (% He in Solar System) |
Half-life (t1/2) | stable |
Isotope mass | 3.0160293 Da |
Spin | 1⁄2 |
Parent isotopes | 3H (beta decay of tritium) |
Isotopes of helium Complete table of nuclides |
Helium-3 (3He[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.
Helium-3 occurs as a primordial nuclide, escaping from Earth's crust into its atmosphere and into outer space over millions of years. It is also thought to be a natural nucleogenic and cosmogenic nuclide, one produced when lithium is bombarded by natural neutrons, which can be released by spontaneous fission and by nuclear reactions with cosmic rays. Some found in the terrestrial atmosphere is a remnant of atmospheric and underwater nuclear weapons testing.
Nuclear fusion using helium-3 has long been viewed as a desirable future energy source. The fusion of two of its atoms would be aneutronic, not release the dangerous radiation of traditional fusion or require much higher temperatures.[3] The process may unavoidably create other reactions that themselves would cause the surrounding material to become radioactive.[4]
Helium-3 is thought to be more abundant on the Moon than on Earth, having been deposited in the upper layer of regolith by the solar wind over billions of years,[5] though still lower in abundance than in the Solar System's gas giants.[6][7]