Antimony (51Sb) occurs in two stable isotopes, 121Sb and 123Sb.
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 half-life 5.76 days.
Except for beryllium, antimony is the lightest element observed to have isotopes capable of alpha decay; 104Sb is seen to undergo this mode of decay.
Some light elements, namely those near 8Be, have isotopes with delayed alpha emission (following proton or beta emission) as a rare branch.