A study od CD and Te isotopes in the interacting boson approximation

An investigation of the properties of the Cd and Te isotopes is performed in the framework of the interacting boson approximation. Particular attention is paid to the presence of 'intruder' 0+ and 2+ states at the energy of the two-phonon triplet in the middle-shell Cd isotopes. It is suggested that these states originate from two-particle two-hole proton excitations across the shell gap at Z = 50. The behaviour of these states is studied as a function of the neutron number. No clear evidence of similar phenomena is observed in the Te isotopes. The collectives features of these nuclei are found to be in satisfactory agreement with the predictions of the neutron-proton interacting boson model. (orig.)