Low-lying dipole excitations in the stable Cd isotopes: a systematics

Low-lying dipole excitations in the medium-weight vibrational nuclei of the Cd isotopic chain were investigated by means of nuclear resonance fluorescence experiments performed at the bremsstrahlung beam of the Stuttgart Dynamitron accelerator (endpoint energy 4.1 MeV). Detailed information has been obtained on excitation energies, spins, decay widths, and transition probabilities of numerous excited states in 110–114,116Cd. Additionally, the use of two Compton polarimeters enabled model-independent parity assignments for excitations in the even-even isotopes. Strongly excited Jπ = 1− states are found in all even-even Cd nuclei at excitation energies near the sumof the energies of the first 2+ and 3− states. These excitations are interpreted as the 1− member of the quadrupole-octupole coupled quintuplet (2+⊗3−). The fragmented strength observed in the odd isotopes 111,113Cd is compared with the strength distributions in the neighboring even-even Cd isotopes.