Isotopes of lanthanum
Naturally occurring lanthanum is composed of one stable and one radioactive isotope, with the stable isotope, 139La, being the most abundant. There are 38 radioisotopes that have been characterized, with the most stable being 138La, with a half-life of 1.02×1011 years; 137La, with a half-life of 60,000 years and 140La, with a half-life of 1.6781 days. The remaining radioactive isotopes have half-lives that are less than a day and the majority of these have half-lives that are less than 1 minute. This element also has 12 nuclear isomers, the longest-lived of which is 132mLa, with a half-life of 24.3 minutes.
The isotopes of lanthanum range in atomic weight from 116.95 u to 154.96 u.
