Editing Lanthanum (section)

===Isotopes===
[[File:Lanthanum stable nucleus.png|thumb|left|280px|Excerpt from the [[chart of nuclides]] showing stable isotopes (black) from barium ({{nobr| {{mvar|Z}} {{=}} 56 }}) to neodymium ({{nobr| {{mvar|Z}} {{=}} 60 }})]]
{{Main|Isotopes of lanthanum}}
Naturally occurring lanthanum is made up of two isotopes, the stable {{chem|139|La}} and the [[primordial nuclide|primordial long-lived radioisotope]] {{chem|138|La}}. {{chem|139|La}} is by far the most abundant, making up 99.910% of natural lanthanum: it is produced in the [[s-process]] (slow [[neutron]] capture, which occurs in low- to medium-mass stars) and the [[r-process]] (rapid neutron capture, which occurs in core-collapse [[supernova]]e). It is the only stable isotope of lanthanum.<ref name=Audi>{{NUBASE 2003}}</ref> The very rare isotope {{chem|138|La}} is one of the few primordial [[odd–odd nuclei]], with a long half-life of {{nobr|1.05×{{10^|11}} years.}} It is one of the proton-rich [[p-nuclei]] which cannot be produced in the [[s-process|s-]] or [[r-process]]es. {{chem|138|La}}, along with the even rarer [[tantalum-180m|{{chem|180m|Ta}}]], is produced in the ν-process, where [[neutrino]]s interact with stable nuclei.<ref name=nu-process>{{cite journal |last1=Woosley |first1=S.E. |last2=Hartmann |first2=D.H. |last3=Hoffman |first3=R.D. |last4=Haxton |first4=W.C. |year=1990 |title=The ν-process |journal=The Astrophysical Journal |volume=356 |pages=272–301 |bibcode=1990ApJ...356..272W |doi=10.1086/168839}}</ref> All other lanthanum isotopes are [[synthetic radioisotope|synthetic]]: With the exception of {{chem|137|La}} with a half-life of about 60,000&nbsp;years, all of them have half-lives less than two days, and most have half-lives less than a minute. The isotopes {{chem|139|La}} and {{chem|140|La}} occur as [[fission product]]s of uranium.<ref name=Audi/>