Explanation of the backangle anomaly and the isotope effect within a microscopic study of elastic α-scattering on the even Ca isotopes

Elastic α-scattering on the isotopes ^40,42,44,48Ca has been studied microscopically within the framework of the generator coordinate method. For energies above the Coulomb barrier the backangle enhancement of the cross section in elastic α-⁴⁰Ca scattering is explained by several overlapping barrier resonances, while for energies below the barrier the backangle rise is caused by individual long-living resonances which — in agreement with recent experimental data — confirm the concept of an “α-⁴⁰Ca quasimolecule”. The isotope effect showing up in a different behaviour of the cross section at backangles is due to a different absorptive strength of the isotopes. “Neutron blocking” has been ruled out as a possible explanation of the isotope effect.