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 113Cd (beta decay, half-life is ) and 116Cd (two-neutrino double beta decay, half-life is ). The other three are 106Cd, 108Cd (both double electron capture), and 114Cd (double beta decay); only lower limits on these half-lives have been determined. At least three isotopes – 110Cd, 111Cd, and 112Cd – are stable. Among the isotopes that do not occur naturally, the most long-lived are 109Cd with a half-life of 462.6 days, and 115Cd 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 113mCd ("t"1⁄2 = 14.1 years), 115mCd ("t"1⁄2 = 44.6 days), and 117mCd ("t"1⁄2 = 3.36 hours).