Isotopes of antimony
occurs naturally as two stable isotopes, Sb and Sb. There are 37 artificial radioactive isotopes known with mass numbers 104 to 142, the lightest two of which are beyond the proton drip line. Isotopes that are lighter than the stable isotopes tend to decay by β+, and those that are heavier tend to decay by β−; the intermediate Sb is observed to decay in both ways.
The most stable radioisotope of antimony is the minor fission product Sb, with a half-life of 2.758 years; Sb, with half-life 60.20 days; and Sb, with half-life 12.35 days. All other isotopes have half-lives less than 4 days, most less than an hour. Of the numerous isomers reported, the longest-lived is Sb with half-life 5.76 days; this nuclide has not been confirmed not to be the ground state.