Dipole excitations in the transitional nucleus144Nd studied in photon scattering experiments

Low-lying electric and magnetic dipole excitations in the transitional nucleus ${}^{144}$Nd have been studied in nuclear resonance fluorescence experiments performed with a bremsstrahlung beam (end point energy 4.1 MeV). The use of high-resolution $\gamma$-ray spectrometers and a sectored single-crystal Compton polarimeter provided detailed information on excitation energies, spins, parities, decay widths, transition probabilities, and branching ratios of numerous new spin-1 states in ${}^{144}$Nd. The strong $E$1 excitation at 2185 keV in this $N$ = 84 nucleus is interpreted as the quadrupole-octupole coupled two-phonon excitation which has been observed systematically in the neighboring $N$ = 82 isotones. The decay properties of this 1${}^{-}$ state are compared with the systematics of the low-lying 1${}^{-}$ levels in the other even-even, stable Nd isotopes. The $M$1 excitations in ${}^{144}$Nd are discussed with respect to the deformation dependence of the orbital $M$1 “scissors mode,” the so-called “${\delta }^2$ law,” which has been studied previously in the other stable even-even Nd nuclei and in the Sm isotopes.