Isotopes of erbium
Naturally occurring erbium (68Er) is composed of six stable isotopes, with 166Er being the most abundant (33.503% natural abundance). Radioisotopes have been characterized with from 145Er to 175Er, all having half-lives less than ten days: the most stable are 169Er (9.39 days), 172Er (49.3 hours), and 160Er (28.58 hours).