The angular distributions of alpha-particles emitted by oriented nuclei and their relation to nuclear structure and deformation

alpha-particle angular distribution data from an extensive on-line nuclear orientation study of the favoured decay of nearly spherical, neutron deficient At and Rn nuclei near N=126, as well as of deformed Fr and Pa isotopes are presented.:From the comparison of these data with various theoretical models it is found that for nearly spherical nuclei, anisotropic alpha-emission in favoured decays can be well explained within the shell model but not by a tunnelling model. On the other hand, for the deformed nuclei studied here, a description on the basis of alpha-particle tunelling through the Coulomb barrier is quite appropriate.