Structural changes at large angular momentum in neutron-rich $^{121,123}$Cd

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