Atomic nuclei decay modes by spontaneous emission of heavy ions.

Abstract

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 trans-lead nuclei, where the minimum lifetime is obtained from parent-emitted heavy ion combinations leading to a magic ${(}^{208}$Pb) or almost magic daughter nucleus. More than 140 nuclides with atomic number smaller than 25 are possible candidates to be emitted from heavy nuclei, with half-lives in the range of ${10}^{10}$--${10}^{30}$ s: $^{5}\mathrm{He}$, $^{8--10}\mathrm{Be}$, $^{11}$,12B, $^{12--16}\mathrm{C}$, $^{13--17}\mathrm{N}$, $^{15--22}\mathrm{O}$, $^{18--23}\mathrm{F}$, $^{20--26}\mathrm{Ne}$, $^{23--28}\mathrm{Na}$, $^{23--30}\mathrm{Mg}$, $^{27--32}\mathrm{Al}$, $^{28--36}\mathrm{Si}$, $^{31--39}\mathrm{P}$, $^{32--42}\mathrm{S}$, $^{35--45}\mathrm{Cl}$, $^{37--47}\mathrm{Ar}$, $^{40--49}$ K, $^{42\mathrm{\ensuremath{-}}51.\phantom{\rule{0ex}{0ex}}.\phantom{\rule{0ex}{0ex}}.}\mathrm{Ca}$, $^{44--53}$ Sc, $^{46--53}\mathrm{Ti}$, $^{48--54}\mathrm{V}$, and $^{49--55}$ Cr. The shell structure and the pairing effects are clearly manifested in these new decay modes.