Three-Quasiparticle States inLa139

Absolute differential cross sections of transitions to levels in the $N=82\mathrm{}$ nucleus ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}$ populated by the reaction ${}_{}{}^{138}{}_{}{}^{}\mathrm{La}\mathrm{}(d,p)\mathrm{}{}_{}{}^{139}{}_{}{}^{}\mathrm{La}$ at 12-MeV bombarding energy have been measured with a magnetic spectrograph. The $Q$ value of the reaction is 6553 ± 3 keV. The reaction strongly populates the one-quasiproton ground state of ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}$ by $l=2\mathrm{}$ neutron transfer, which establishes positive parity for the ${}_{}{}^{138}{}_{}{}^{}\mathrm{La}$ ground state. Of the many known states in the region from 1200 to 2000 keV in ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}$, only the 1536.3-keV state is weakly populated. The reaction strongly populates a high density of three-quasiparticle states in ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}$, beginning at 3355-keV excitation energy, by $l=3\mathrm{}$ neutron transfer. The shell-model multiplet structure of ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}$ has been calculated using a modified surface $\delta$ interaction within a configuration space having ($1g_{\frac{7}{2}}$) and ($2d_{\frac{5}{2}}$) active proton orbitals and ($3s_{\frac{1}{2}}$), ($2d_{\frac{3}{2}}$), ($2f_{\frac{7}{2}}$), and ($3p_{\frac{3}{2}}$) active neutron orbitals. Comparisons between experimental and theoretical multiplet structure are presented.