The great majority of the known nuclides with Z > 40, including the so-called stable nuclides, are metastable with respect to several modes of spontaneous superasymmetric splitting. A model extended from the fission theory of alpha decay allows one to estimate the lifetimes and the branching ratios relative to the alpha decay for these natural radioactivities. From a huge amount of systematic calculations it is concluded that the process should proceed with maximum intensity in the translead nuclei, where the minimum lifetime is obtained from parent-emitted heavy ion combinations leading to a magic ( 2 0 8~b ) or almost magic daughter nucleus. More thari 140 nuclides with atomic number smaller than 25 are possible candidates to be emitted from heavy nuclei, with half-lives in the range of