The study of the coupling of various collective excitations is of great interest in nuclear structure physics. The crucial question is to what extent the fundamental building blocks of collective excitations can be combined. A particularly interesting problem is the coupling of the lowest quadrupole and octupole modes in nuclei. We report on first evidence for the complete quadrupole-octupole coupled quintuplet of negative parity ${(2\mathrm{}}_1^{+}\otimes 3_1^{-}{)}^{{(J}^{-})}$ with $J=1,$ 2, 3, 4, 5 in ${}^{108}\mathrm{Cd},$ the fourth full multiplet ever proposed. Excited states of ${}^{108}\mathrm{Cd}$ were populated in $\beta$ decay and with a nonselective $(\alpha ,n)$ fusion-evaporation reaction. The analysis of $\gamma \gamma$ angular correlations served to assign spin values to excited states and to determine multipole mixing ratios of transitions. This powerful combination of experiments and methods resulted in a huge amount of new data allowing us to present a detailed discussion of the quadrupole-octupole coupled multiplet in ${}^{108}\mathrm{Cd}$ based on excitation energies, branching ratios, and multipole mixing ratios and also present a comparison with the well studied neighbor ${}^{112}\mathrm{Cd}.$ The energy splitting within the multiplet is calculated in the vibrational limit of the sdf interacting boson model using a simple Hamiltonian, which results in an analytical single-parameter description for the energies.

• Received 28 February 2002

DOI:https://doi.org/10.1103/PhysRevC.66.014304