Isospin properties of electric dipole excitations in 48Ca

Two different experimental approaches were combined to study the electric dipole strength in the doubly-magic nucleus Ca-48 below the neutron threshold. Real-photon scattering experiments using bremsstrahlung up to 9.9 MeV and nearly mono-energetic linearly polarized photons with energies between 6.6 and 9.51 MeV provided strength distribution and parities, and an (alpha, alpha'gamma) experiment at E-alpha = 136 MeV gave cross sections for an isoscalar probe. The unexpected difference observed in the dipole response is compared to calculations using the first-order random-phase approximation and points to an energy-dependent isospiu character. A strong isoscalar state at 7.6 MeV was identified for the first time supporting a recent theoretical prediction. (C) 2014 The Authors. Published by Elsevier B.V.