Isotopes of antimony

Antimony (₅₁Sb) occurs in two stable isotopes, ¹²¹Sb and ¹²³Sb. There are 35 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.

There are also many isomers, the longest-lived of which is ^120m1Sb with a half-life of 5.76 days.

With the exception of beryllium, antimony is the lightest element observed to have isotopes capable of undergoing alpha decay, with the isotope ¹⁰⁴Sb being seen to undergo this mode of decay. Some lighter elements, namely those in the vicinity of ⁸Be, have isotopes with delayed alpha emission (following proton or beta emission) as a rare branch.