Isotopes of cadmium

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Naturally occurring cadmium (₄₈Cd) is composed of 8 isotopes. For two of them, natural radioactivity was observed, and three others are predicted to be radioactive but their decays have not been observed, due to extremely long half-lives. The two natural radioactive isotopes are ¹¹³Cd (beta decay, half-life is 8.04 × 10¹⁵ years) and ¹¹⁶Cd (two-neutrino double beta decay, half-life is 2.8 × 10¹⁹ years). The other three are ¹⁰⁶Cd, ¹⁰⁸Cd (double electron capture), and ¹¹⁴Cd (double beta decay); only lower limits on their half-life times have been set. Three isotopes—¹¹⁰Cd, ¹¹¹Cd, and ¹¹²Cd—are theoretically stable. Among the isotopes absent in natural cadmium, 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 that are less than 2.5 hours and the majority of these have half-lives that are less than 5 minutes. This element also has 12 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).

The known isotopes of cadmium range in atomic mass from 94.950 u (⁹⁵Cd) to 131.946 u (¹³²Cd). The primary decay mode before the second most abundant stable isotope, ¹¹²Cd, is electron capture and the primary modes after are beta emission and electron capture. The primary decay product before ¹¹²Cd is element 47 (silver) and the primary product after is element 49 (indium).

A 2021 study has shown at high ionic strengths, Cd isotope fractionation mainly depends on its complexation with carboxylic sites. At low ionic strengths, nonspecific Cd binding induced by electrostatic attractions plays a dominant role and promotes Cd isotope fractionation during complexation.^[4]