Helium-4 makes up about one quarter of the ordinary matter in the universe by mass, with almost all of the rest being hydrogen. While nuclear fusion in stars also produces helium-4, most of the helium-4 in the Sun and in the universe is thought to have been produced during the Big Bang, known as " primordial helium".

Properties and data of the isotope 4 He. See also: list of Helium isotopes. Direct parent isotopes are: 5 He, 5 Li, 6 Be. The following table shows the atomic nuclei that are isotonic (same neutron number N = 2) and isobaric (same nucleon number A = 4) with Helium-4.

Helium (2 He) (standard atomic weight: 4.002 602 (2)) has nine known isotopes, but only helium-3 (3 He) and helium-4 (4 He) are stable. [4] All radioisotopes are short-lived; the longest-lived is 6 He with half-life 806.92(24) milliseconds .

alpha particle, positively charged particle, identical to the nucleus of the helium -4 atom, spontaneously emitted by some radioactive substances, consisting of two protons and two neutrons bound together, thus having a mass of four units and a positive charge of two.

Helium-4 (also written 4 He) is an isotope of helium. It is the most common isotope of helium in the universe. Out of all the helium on the Earth, 99.99986% is helium-4. The nucleus (the center) of a helium-4 atom is also known as the alpha particle.

Superfluid helium-4 (helium II or He-II) is the superfluid form of helium-4, an isotope of the element helium. A superfluid is a state of matter in which matter behaves like a fluid with zero viscosity.

Helium-4 (4He) is a stable isotope of the element helium. It is by far the more 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. This article needs additional citations for verification.