Ground state to ground state alpha decays of heavy even-even nuclei

Abstract

The authors examine the experimental data on partial half lives for alpha decay of heavy even-even nuclei. When presented in the traditional form of Geiger-Nuttall plots (1911) for various isotopic sequences, these data clearly indicate the existence of different linear relations for neutron numbers N above and below the magic value of 126. They present a simple cluster model, employing three fixed parameters, which is able to give an excellent account of all these half lives. In particular, it can reproduce the values for all even-even nuclei having 76<or=Z<or=100 to within a factor of approximately two. An important feature of the model is that it envisages preformed alpha particles in the parent nuclei to be moving in orbits with a large value of a global quantum number. The discontinuity in the Geiger-Nuttall plots at N=126 is then naturally explained by an increase of this global quantum number as the alpha particle is forced into a higher orbit by the shell closure.