Structural changes at large angular momentum in neutron-richCd121,123

Prompt γ rays of isotopically identified neutron-rich isotopes of Cd, produced in transfer- and fusion-fission induced by the 238U beam at 6.2 MeV/u on a 9Be target, were measured using the EXOGAM γ -ray detector array and the magnetic spectrometer VAMOS++. New results for the level scheme of 121,123Cd, extending to relatively large angular momentum are reported. The energy levels above 2-MeV excitation energy, are found to differ from those observed in lighter isotopes of Cd indicating a change in structure in these more neutron-rich nuclei. These states are not explained by large-scale shell model calculations, that explain well the structure of the underlying Sn isotopes and the neighboring even-A Cd isotopes. The present data, especially for the odd-A nuclei, point to a deficiency in the matrix elements related to the p-n residual interaction and provide a new domain for testing widely used shell model interactions employed for understanding the evolution of structure in neutron-rich nuclei.