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Helium-4 makes up about one quarter of the ordinary matter in the universe by mass, with almost all of the rest being hydrogen. When liquid helium-4 is cooled to below 2.17 K (−270.98 °C), it becomes a superfluid, with properties that are very unlike those of an ordinary liquid.
Helium 4 is a complete tetrahedron. It consists of 4 protons in a triangular shape with 2 inner electrons. The other 2 electrons are in the outer orbital (complete S-orbital). He4 is stable and can be seen as 2 Deuterium nuclei merged together.
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. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.
4 He forms the bulk of naturally occurring helium, but the lighter isotope 3 He has been formed, since about 1950, in experimentally useful quantities by the decay of tritium produced in nuclear reactors.
27 Ιαν 2021 · The 2S–2P transitions in muonic helium-4 ions are measured using laser spectroscopy and used to obtain an α-particle charge-radius value five times more precise than that from electron scattering.
A Bohr model of a neutral helium-4 atom is shown below. In this model, the electrons are represented as black dots that sit on a ring around the nucleus. The nucleus is shown as one green circle in the center.
one helium 4 rich and one helium-3 rich. The He-3 rich phase will float on top of the He-4 rich phase. At zero temperature the He-3 rich phase becomes “pure” i.e. 100% He-3, whereas the He-4 rich phase always contains some He-4 (6.4% or more).
