Excited levels in ${}^{144}$Nd below 3.3 MeV have been studied using the ${(n,n}^{\prime }\gamma )$ reaction. Electromagnetic transition probabilities, multipole-mixing and branching ratios, and level spins and parities were deduced from measured $\gamma$-ray excitation functions, angular distributions, and Doppler shifts. Mixed-symmetry configurations in low-lying excited states were investigated by comparing experimental electromagnetic transition rates with theoretical calculations made using the interacting boson model and with existing calculations from the quasiparticle phonon model, the cluster vibrator model, and the particle-core coupling model. Fragmentation of the $2^{+}$ mixed-symmetry mode is clearly observed through strong $M1\mathrm{}$ transitions into the lowest symmetric $2^{+}$ level and through small $E2/M1\mathrm{}$ multipole-mixing ratios. Comparisons with similar measurements on ${}^{142}\mathrm{Ce}$ reveal that these $N=84\mathrm{}$ isotones exhibit strong fragmentation of the mixed-symmetry mode, although it appears to be spread into more levels in ${}^{144}\mathrm{Nd}$. Evidence is found to support the assignment of the 2779.0-keV level as the $3^{-}$ member of the octupole-quadrupole phonon coupled quintuplet in ${}^{144}\mathrm{Nd}$ and to propose that this excited mode is shared with the 2606.0-keV state. Two- and three-quadrupole phonon excitations, as well as other members of the quadrupole-octupole quintuplet, are also examined.

• Received 12 January 1998

DOI:https://doi.org/10.1103/PhysRevC.57.2264