Alpha-particle angular distributions of At and Rn isotopes and their relation to nuclear structure

We report on an extensive on-line nuclear orientation study of the angular distribution of alpha particles emitted in the favored decay of neutron deficient At and Rn nuclei near the N = 126 shell closure. Surprisingly large anisotropies were observed, showing pronounced changes from one isotope to another. Comparing these data with several theoretical models shows that anisotropic alpha emission in favored decays from near-spherical nuclei can well be explained within the shell model, implying that it is mainly determined by the structure of the decaying nucleus.