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]]