Helium-4

Helium-4 (^4He) is a non-radioactive isotope of the element helium. It is by far the most abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on Earth. Its nucleus is identical to an alpha particle, and consists of two protons and two neutrons.

Properties

Helium-4 is a boson, with its nucleus obeying Bose–Einstein statistics. It becomes a liquid at very low temperatures, in a phase known as helium II, which exhibits very unusual properties due to quantum mechanical effects. Among these properties is superfluidity, which allows it to flow without viscosity or resistance to flow. Helium-4 also has a very low boiling point, which makes it useful in cryogenics and in cooling superconducting magnets.

Occurrence

Helium-4 is produced by both nuclear fusion in the cores of stars and by the radioactive decay of heavy elements in the Earth's crust, a process known as alpha decay. The vast majority of the Earth's helium-4, however, comes from the alpha decay of uranium and thorium.

Applications

Due to its unique properties, helium-4 has several important applications. It is used in cryogenics, particularly in the cooling of superconducting magnets, such as those used in magnetic resonance imaging (MRI) machines. It is also used in quantum computing, fiber optics, and in the study of superfluidity and other quantum mechanical effects at low temperatures.

Isotopes

While helium-4 is the most common isotope, helium also has a less abundant isotope, helium-3, which has one fewer neutron. Helium-3 has applications in nuclear fusion research and low-temperature physics.

See also

• Helium
• Isotope
• Superfluidity
• Cryogenics
• Quantum mechanics