Study of the levels in 1400La using the 139La(ngamma)140La reaction

The levels in 140La have been studied following thermal-neutron capture in 139La using Ge(Li), Si(Li), curved-crystal, and coincidence spectrometers. The neutron binding energy of 140La was determined as 5161.1±1.0 keV. The data, when combined with the previous 139La(d, p)140La study, allow the assignment of the first 14 states up to 581.060 keV to the mixed configurations πg7/2νf7/2 and πd5/2νf7/2.

The energies of states in keV (spin parity) are: 0 (3-), 29.965 (2-), 34.656 (5-), 43.811 (1-), 48.865 (6-), 63.171 (4-), 103.803 (6-), 162.656 (2-), 272.311 (4-), 284.634 (7-), 318.214 (3-), 322.003 (5-), 467.505 (1-), 581.060 (0-). Comparisons of γ-ray branching ratios and (d, p) cross sections with the predictions of a quasiparticle model for odd-odd nuclei allow a relatively uncompromised solution for the state vectors for the first 14 states.

The success of this model implies that there is little phonon or four-quasiparticle admixture through the level at 581.060 keV. A detailed experimental study of additional levels up to 1055 keV has been performed. © 1970 The American Physical Society