The excited levels of ${}_{}{}^{142}{}_{}{}^{}\mathrm{Ce}$ have been studied using the (n,${\mathit{n}}^{\prime }$γ) reaction. Excitation functions, angular distributions, and Doppler shifts were measured for γ rays from levels up to an excitation energy of 3.3 MeV; multipole-mixing and branching ratios and transition rates were deduced. Theoretical predictions of electromagnetic transition rates were compared for the interacting boson model, the quasiparticle phonon model, and the particle-core coupling model with experimental values. Evidence is found supporting the fragmentation of mixed-symmetry strength among neighboring ${}_{}{}^{142}{}_{}{}^{}\mathrm{Ce}$ excited levels. This fragmentation is evinced in the $2^{+}$ excitations through strong M1 transitions; however, the $3^{+}$ mixed-symmetry strength is not manifested directly through strong M1 transitions, but rather is implied through model calculations. Candidates for multiphonon excitations are identified for the three-quadrupole and quadrupole-octupole phonon quintets.

• Received 7 July 1995

DOI:https://doi.org/10.1103/PhysRevC.52.2387