كم عدد نظائر الكادميوم؟
Naturally occurring cadmium (Cd) is composed of 8 isotopes. For two of them, natural radioactivity was observed, and three others are predicted to be radioactive but their decays were never observed, due to extremely long half-lives. The two natural radioactive isotopes are <sup>113</sup>Cd (beta decay, half-life is 8.04 × 10<sup>15</sup> years) and <sup>116</sup>Cd (two-neutrino double beta decay, half-life is 2.8 × 10<sup>19</sup> years). The other three are <sup>106</sup>Cd, <sup>108</sup>Cd (double electron capture), and <sup>114</sup>Cd (double beta decay); only lower limits on their half-life times have been set. At least three isotopes—<sup>110</sup>Cd, <sup>111</sup>Cd, and <sup>112</sup>Cd—are absolutely stable. Among the isotopes absent in the natural cadmium, the most long-lived are <sup>109</sup>Cd with a half-life of 462.6 days, and <sup>115</sup>Cd 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 <sup>113m</sup>Cd (t 14.1 years), <sup>115m</sup>Cd (t 44.6 days) and <sup>117m</sup>Cd (t 3.36 hours).
8