Study of the Levels inLa140Using theLa139(n, γ)La140Reaction

The levels in ${}_{}{}^{140}{}_{}{}^{}\mathrm{La}$ have been studied following thermal-neutron capture in ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}$ using Ge(Li), Si(Li), curved-crystal, and coincidence spectrometers. The neutron binding energy of ${}_{}{}^{140}{}_{}{}^{}\mathrm{La}$ was determined as 5161.1±1.0 keV. The data, when combined with the previous ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}(d, p){}_{}{}^{140}{}_{}{}^{}\mathrm{La}$ study, allow the assignment of the first 14 states up to 581.060 keV to the mixed configurations $\pi g_{\frac{7}{2}}\nu f_{\frac{7}{2}}$ and $\pi d_{\frac{5}{2}}\nu f_{\frac{7}{2}}$. 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 $\gamma$-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.