Abstract
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.
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