Study of 149Ce levels populated in the β− decay of 149La and signature splitting of the neutron i13/2 band Original Research Article

The low-energy structure of the N=91 149Ce nucleus has been studied by means of γ- and X-ray spectroscopy following the β− decay of 149La. The decay scheme of 149La→149Ce was constructed for the first time. The new data complement and correct some of the information deduced from earlier prompt γ-ray studies of spontaneous fission of 252Cf and 248Cm. As a result, a consistent band structure of 149Ce has been established for those bands, which have band heads located below an excitation energy of 400 keV. Two sets of levels, with similar energies and extending to high spins, are established as two signature members of the νi13/2 rotational band with dominant configuration 3/2+[651]. Systematics of splitting in the νi13/2 bands in lighter N=91 isotones are also provided. The Nilsson assignment for the band was confirmed by the Self-Consistent Total Routhian Surface calculations as well as by the extended Nilsson model with the inclusion of pairing and Coriolis interactions.