Probing isospin mixing with the giant dipole resonance in the Zn 60 compound nucleus

An experimental study of the isospin mixing in the mass region A=60 was made by measuring the γ decay from the giant dipole resonance in the compound nuclei Zn60 and Zn62. These compound nuclei were populated at two different excitation energies, E∗=47 MeV and E∗=58 MeV using the fusion evaporation reactions S32+Si28 at the bombarding energy of 86 and 110 MeV and S32+Si30 at 75 and 98 MeV. In the experiment, performed at the Laboratori Nazionali di Legnaro of the Istituto Nazionale di Fisica Nucleare (INFN), the γ rays were measured with the GALILEO detection system in which large-volume LaBr3(Ce) detectors were added to the HPGe detectors. The Coulomb spreading width was obtained from the comparison of the two reactions and then the isospin mixing parameter at zero temperature and the isospin-symmetry-breaking correction for beta decay were deduced. The present results were compared with data of the same type in other mass regions and with data from mass and beta-decay measurements and with theory. The present data allow us to deduce for the first time a consistent picture for mass dependence of isospin mixing and for the corresponding correction for the beta decay, supporting a reliable extension to the very interesting region of Sn100.