Dipole and electric quadrupole excitations in 40,48Ca

Photon scattering experiments have been performed to investigate the structure of the two doubly magic nuclei 40,48Ca. The method is highly selective to induce low-order multipole transitions i.e., E1, M1, and E2 from the ground state. We determined the energies and spins of excited states and the absolute strengths of the γ-decays in a model independent way. We find the summed electric dipole strengths below 10 MeV to exhaust the energy weighted sum rule (EWSR) by 0.023% and 0.27%, respectively. The summed electric quadrupole strengths are Σ B(E2) ↑ = 332 e2fm4 and 407 e2fm4 for 40Ca and 48Ca, respectively. In order to explain the difference in the E1 strengths of the two isotopes several theoretical models are discussed. (orig.)