High Quality Content by WIKIPEDIA articles! Antimony (Sb) occurs in two stable isotopes, 121Sb and 123Sb. There are thirty-five artificial radioactive isotopes, the longest-lived of which are 125Sb with a half-life of 2.75856 years, 124Sb with a half-life of 60.2 days, and 126Sb with a half-life of 12.35 days. All other isotopes have half-lives less than 4 days, most less than an hour.