Alpha-Alpha Scattering from 12.88 to 21.62 Mev

The differential scattering cross section of alpha particles on helium has been investigated as a function of energy in the range from 12.88 to 21.62 Mev. The data obtained indicate a very strong angular dependence. This further appears to be a fairly sensitive function of energy. At the lower excitations there is a rather singular interference between the Coulomb and nuclear interactions. Above 20 Mev, interferences among the various components of the nuclear phase shifts again give rise to marked singularities. These data have been analyzed with respect to the phase shifts arising from the angular momentum components of the interaction. This decomposition indicated resonances at 7.55 and 10.8 Mev with widths, $\Gamma$ of 1.2 Mev in each case and state assignments of 0 and 4, respectively.