Ba137(n, γ)Reaction and Level Structure ofBa138

The $\gamma$ rays from the ${\mathrm{Ba}}^{137}(n, \gamma ){\mathrm{Ba}}^{138}$ reaction have been studied both in singles and coincidence with a 9-${\mathrm{cm}}^3$ Ge(Li) detector and a Ge(Li)-NaI combination. Of a total of 91 $\gamma$ rays, 15 have been identified as primary transitions de-exciting the compound nucleus. These data, together with the information obtained from coincidence spectra and from previous studies, establish 18 levels in ${\mathrm{Ba}}^{138}$ with energies 1435.7±0.2, 1898.7±0.5, 2189.6±0.5, 2217.6±1.0, 2307.7±0.7, 2445.6±0.5, 2582.7±0.4, 2638.8±0.5, 2880.7±0.3, 3051.4±2.0, 3340.0±1.5, 3503.0±2.0, 3643.4±1.5, 3921.7±1.5, 4241.9±2.0, 4280.4±2.0, 4287.5±2.0, and 4360.2±2.0 keV. In addition, six pairs of $\gamma$ rays whose energies sum to equal the binding energy were found, but the order of the cascades could not be established. The neutron separation energy was found to be 8611.3±0.8 keV. The prominent 5730.4-keV primary $\gamma$ ray feeds the level at 2880.7 keV, which is identified with the $3^{-}$ state seen in inelastic scattering experiments with charged particles. The level decays predominantly by the 1445.0-1435.7-keV $\gamma$-ray cascade through the $2^{+}$ first excited state. The relation between states excited in ($p, p^{\prime }$) and ($d, p$) reactions and those observed in the present experiment is discussed.