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 nuc lear orientation study of the favoured decay of nearly spherical, neut ron deficient At and Rn nuclei near N=126, as well as of deformed Fr a nd Pa isotopes are presented.:From the comparison of these data with v arious 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 han d, for the deformed nuclei studied here, a description on the basis of alpha-particle tunelling through the Coulomb barrier is quite appropr iate.