Helium4

Helium-4, also written as 4He, is the most common isotope of helium. Its nucleus contains two protons and two neutrons, giving it a mass number of 4 and an atomic number of 2. A neutral 4He atom has two electrons. The nucleus is unusually strongly bound and has total spin 0, making 4He a boson.

Natural abundance and origin: In nature, helium is almost entirely 4He; traces of 3He exist in some reservoirs. Most helium on Earth is produced by alpha decay of heavier elements and from primordial sources. In the universe, 4He was produced in the Big Bang during nucleosynthesis and accounts for about 25% of baryonic mass by weight, a key signature of early-universe chemistry.

Physical properties: Helium-4 is a noble gas with the lowest boiling point of any element—4.22 K at 1 atm (−268.93 °C). It remains a liquid at cryogenic temperatures and can become a superfluid below 2.177 K, exhibiting frictionless flow. It is chemically inert and nonreactive under ordinary conditions, and remains colorless and odorless as a gas.

Applications and significance: Liquid helium-4 is essential for cooling superconducting magnets in MRI machines and in various scientific instruments. It is also used as a protective gas and in cryogenics, leak detection, and other technologies requiring extreme cooling and inert atmospheres. The 4He nucleus is the reference for alpha radiation and alpha particles in nuclear physics.

Safety: Helium is non-toxic but acts as an asphyxiant in confined spaces and presents hazards from extreme cold and high-pressure containment. Proper handling and ventilation are important to prevent oxygen displacement and cold-burn injuries.