Helium-4
1012996
226130918
2008-07-16T23:19:23Z
JWB
273993
infobox isotope
{{infobox isotope
| background = #F99
| isotope_name = Helium-4
| alternate_names =Helium-4,He-4
| symbol =He
| mass_number =4
| mass =3.016
| num_neutrons =2
| num_protons =2
| abundance =99.999863%
| halflife =stable
| error_halflife =
| text_color =
| image =
| 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 [[proton]]s and two [[neutron]]s. [[Alpha decay]] is a common decay mode for many [[radioactive isotope]]s. 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 [[star]]s.
When helium-4 is cooled to below 2.17 [[kelvin]]s (–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 (physical)|model]] of [[classical mechanics]] nor by [[nuclear physics|nuclear]] or [[electrical]] models; it is only understood as a [[quantum mechanics|quantum mechanical]] phenomenon.
{{Isotope|element=Helium
|lighter=[[Helium-3]]
|heavier=[[Helium-5]]
|before=[[Lithium-5]] '''([[proton emission|p]])<br />'''[[Helium-5]] '''([[neutron emission|n]])<br />'''[[Beryllium-6]] '''(2p)
|after=Stable
}}
[[Category:Isotopes of helium]]
{{nuclear-stub}}
[[es:Helio-4]]
[[id:Helium-4]]
[[it:Elio-4]]
[[pt:Helium-4]]
[[ru:Гелий-4]]
[[tr:Helyum-4]]
[[zh:氦-4]]