Isotopes of erbium
Naturally occurring erbium is composed of six stable isotopes, with 166Er being the most abundant. Radioisotopes have been characterized with from 145Er to 175Er, all having half-lives less than ten days: the most stable are 169Er, 172Er, and 160Er. All of the remaining radioactive isotopes have half-lives that are less than 11 hours, and the majority of these have half-lives that are less than 4 minutes. This element also has numerous meta states, with the most stable being 149m1Er.
The primary decay mode before the most abundant stable isotope, 166Er, is electron capture to holmium isotopes, and the primary mode after is beta decay to thulium isotopes. All isotopes of erbium are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed.