Helium-4

infobox isotope
background = #F99
isotope_name = Helium-4
alternate_names =Helium-4,He-4
symbol =He
mass_number =4
mass =4.002602
num_neutrons =2
num_protons =2
abundance =99.999863%
halflife =stable
error_halflife =
text_color =


parent =
parent_symbol =
parent_mass =
parent_decay = Alpha decay
spin =

Helium-4 (ComplexNuclide|Helium|4 or SimpleNuclide|Helium|4) is a non-radioactive and light isotope of 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 a boson and an alpha particle, having two protons and two neutrons. Alpha decay is a common decay mode for many radioactive isotopes. In fact, alpha decay of heavy elements is the source of most naturally occurring helium-4 on earth. Helium-4 is also a byproduct of nuclear fusion in stars.

When helium-4 is cooled to below 2.17 kelvins (–271 °C), it becomes a superfluid, with properties that are very unlike those of an ordinary liquid. For example, if helium-4 is kept in an open vessel, a thin film will climb up the sides of the vessel and overflow. Another name for this property of Helium is Rollin film. This strange behaviour is a result of the Clausius-Clapeyron relation and cannot be explained by the current model of classical mechanics nor by nuclear or electrical models; it is only understood as a quantum mechanical phenomenon.

Isotope|element=Helium
lighter=Helium-3
heavier=Helium-5
before=Lithium-5 (p)
Helium-5 (n)
Beryllium-6 "'(2p)
after=Stable