Isotopes up to helium-10, with two protons and eight neutrons, have been confirmed. Halo nuclei have become an area of intense research. This isotope is thought to consist of a normal helium-4 nucleus surrounded by four neutrons dubbed a 'halo' ( 6He also has a halo of neutrons). The most widely-studied exotic helium isotope is helium-8. Helium-7 also emits a beta particle as well as a gamma ray. Helium-6 decays by emitting a beta particle and has a half life of 0.8 second. The shortest-lived isotope is helium-5 with a half-life of 7.6×10 −22 second. The bizarre nuclear structures of such isotopes may offer insight into the isolated properties of neutrons. Although all exotic helium isotopes decay with a half-life of less than one second, researchers have eagerly created exotic light isotopes through particle accelerator collisions to create unusual atomic nuclei for elements such as helium, lithium, and nitrogen. Exotic helium isotopesĪ subset of exotic light nuclei, the exotic helium isotopes have larger atomic masses than helium's natural isotopes. These differing isotope abundances can be used to investigate the origin of rocks and the composition of the Earth's mantle. The different formation processes of the two stable isotopes of helium produce the differing isotope abundances. Extraplanetary material, such as lunar and asteroid regolith, have trace amounts of helium-3 from being bombarded by solar winds. In stars, however, helium-3 is more abundant, a product of nuclear fusion. Trace amounts are also produced by the beta decay of tritium. There is only a trace amount of helium-3 on Earth, primarily present since the formation of the Earth, although some falls to Earth trapped in cosmic dust. Dilution refrigerators take advantage of the immiscibility of these two isotopes to achieve temperatures of a few millikelvins. It was also formed in enormous quantities during Big Bang nucleosynthesis.Įqual mixtures of liquid helium-3 and helium-4 below 0.8 K will 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).

Helium-4 is an unusually stable nucleus because its nucleons are arranged into complete shells. The most common isotope, helium-4, is produced on Earth by alpha decay of heavier radioactive elements the alpha particles that emerge are fully ionized helium-4 nuclei.

Rocks from the Earth's crust have isotope ratios varying by as much as a factor of ten this is used in geology to study the origin of such rocks. In the interstellar medium, the proportion of He-3 is around a hundred times higher. However, helium is unusual in that its isotopic abundance varies greatly depending on its origin. In the Earth's atmosphere, there is one He-3 atom for every million He-4 atoms. For more details on this topic, see Helium-4.Īlthough there are eight known isotopes of helium, only helium-3 and helium-4 are stable.

Atomic mass of helium