Helium 5 is an artificially produced isotope of the naturally occurring helium gas. Helium is the second lightest element, and heads the noble gas group of the periodic table. It occurs naturally as the helium-2 and helium-3 isotopes, the main sources being the natural gas fields of the United States. The exotic helium isotopes are formed in particle accelerators and include helium-5, helium-6 and helium-7. These all have unusual atomic nuclei, containing different numbers of nuclear particles.
Scientists think that studies of these unusual nuclei may lead to clues about the physical structure of atoms, neutrons and the universe. Helium-5 is the shortest lived of these isotopes, having a half-life of only 7.6×10-22 seconds. The nuclei contain two protons and three neutrons. It is highly unstable, losing neutron to decay to the stable isotope helium-4 very quickly.
Studying this decay and the neutrons produced, and their decay, is helping scientists with their studies of the big bang theory into how the universe started. It is also guiding them in there studies of sub atomic structure, including the strange worlds of up and down quarks and quantum physics. Neutrons actually have a long half-life (about ten minutes) so the neutron that is expelled from the helium-5 nucleus lasts far longer than the nucleus from which it is expelled. The decay of the neutron produces a proton, an electron and a small amount of charge. (n-> p +e +v)
Similar experiments are being carried out with other elements, including lithium. The great advantage of helium is its inherent inertness. This makes it relatively easy and safe to work with. The physics of what is occurring inside the nuclei is relatively well understood, and it is the second simplest element to work with in terms of the simplicity of its nuclei. Hydrogen is the only element with a simpler nucleus, but it is highly reactive and so more dangerous to use experimentally. Splitting the hydrogen atom is after all where the hydrogen bomb comes from.
Helium-4 is naturally occurring. It is unique amongst all compounds in that freezing it to absolute zero at normal pressures it remains a liquid, never solidifying. Increasing pressure readily creates a solid though, and increasing the pressure again easily changes the volume of that solid. This has led to its extensive use in cryogenic experimentation and superconductivity studies.
The naturally occurring ratios of helium-3 to helium-4 are being used as a pointer to possible sources of geothermic energy.
