Isospin mixing in the giant dipole resonance of self-conjugate nuclei

Abstract

Several characteristic features of the giant photonuclear dipole cross sections recently computed for 12C, 16O and 40Ca are exhibited and interpreted. They are related to the isospin impurity of the scattering wave functions in the internal region of the compound nucleus. Particular attention is paid to the shape of the cross section in the vicinity of T = 0 resonance states. It is shown that T = 0 states may produce deep minima in some photonuclear cross sections. This indicates that the channel wave functions may play an important role in the violation of the isospin purity in the giant resonances. The example of the giant dipole resonance in 16O is treated in some detail. The physical interpretation of the results of coupled-channel calculations is discussed. It is shown how resonance energies and widths can be obtained.