hélium4

Helium-4 is the most abundant isotope of helium, making up about 99.99986% of all helium found on Earth. Its nucleus consists of two protons and two neutrons, and it has two electrons in its atomic shell. Helium-4 is a stable isotope, meaning it does not undergo radioactive decay. It is produced in stars through nuclear fusion processes, where hydrogen nuclei combine to form helium. On Earth, helium-4 is primarily found trapped in natural gas deposits, often as a byproduct of uranium and thorium decay, which produces alpha particles that are essentially helium-4 nuclei.

The physical properties of helium-4 are notable. It is a colorless, odorless, tasteless, and non-toxic gas at standard temperature and pressure. It has the lowest boiling point of any substance, at -268.93 degrees Celsius (4.22 Kelvin), making it crucial for cryogenic applications. At temperatures below 2.17 Kelvin, helium-4 exhibits superfluidity, a state of matter with zero viscosity, allowing it to flow without resistance. This unique property has been extensively studied in condensed matter physics. Helium-4 is widely used in scientific research, in MRI machines as a coolant for superconducting magnets, in balloons for weather and scientific observations, and in welding as an inert shielding gas.