 Naturally occurring cadmium is composed of 8 isotopes . Two of them are radioactive , and three are expected to decay but have not done so under laboratory conditions . The two natural radioactive isotopes are <unk> ( beta decay , half @-@ life is 7 @.@ 7 × 1015 years ) and <unk> ( two @-@ neutrino double beta decay , half @-@ life is 2 @.@ 9 × <unk> years ) . The other three are <unk> , <unk> ( both double electron capture ) , and <unk> ( double beta decay ) ; only lower limits on these half @-@ lives have been determined . At least three isotopes – <unk> , <unk> , and <unk> – are stable . Among the isotopes that do not occur naturally , the most long @-@ lived are <unk> with a half @-@ life of 462 @.@ 6 days , and <unk> with a half @-@ life of 53 @.@ 46 hours . All of the remaining radioactive isotopes have half @-@ lives of less than 2 @.@ 5 hours , and the majority have half @-@ lives of less than 5 minutes . Cadmium has 8 known meta states , with the most stable being <unk> ( t1 / 2 
