Interacting-boson-fermion-fermion model description of 140La83 and comparison with levels populated by beta decay and neutron capture

We have studied the levels of La140 populated in the beta decay of 140Ba by gamma-ray spectroscopy, which included Compton-suppression gamma-ray spectra of 140Ba sources that were continuously eluted of the La140 daughter activity using ion-exchange chromatographic techniques. The study of the gamma-ray deexcitation of the low-energy levels was completed by a measurement of the low-energy gamma-ray spectrum following thermal neutron capture on 139La. Also, we have performed calculations using the interacting-boson-fermion-fermion model. When we compare the model predictions with the levels and their properties, which we have determined, we find better agreement than has been obtained using quasiparticle-vibrational models