Nuclear resonance fluorescence in Ba-136
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The resonant scattering of electron bremsstrahlung by an enriched sample of $^{136}\mathrm{Ba}$ has been studied for photon energies of up to 5 MeV. It provided estimates of the radiative widths for 10 levels. Based on the relative yields at scattering angles of 96\ifmmode^\circ\else\textdegree\fi{} and 126\ifmmode^\circ\else\textdegree\fi{}, unambiguous spin assignments were made to 5 of these levels. Where feasible, the yield measurements were supplemented by self-absorption data and by linear polarization studies. For the strongest excitation in $^{136}\mathrm{Ba}$, at 3.436 MeV, the resonance fluorescence experiments led to a ${1}^{\ensuremath{-}}$ assignment and a value ${\ensuremath{\Gamma}}_{0}=88\ifmmode\pm\else\textpm\fi{}22$ meV for the partial width of the ground state transition. The corresponding $E1$ strength is approximately $\frac{1}{3}$ of the $E1$ strengths observed for the strongest low-lying $E1$ transitions in the even-even $N=82$ nuclei. When combined with previous observations for $Ng82$, the result obtained for $^{136}\mathrm{Ba}$ ($N=80$) indicates that the strengths of the ground state transitions from the lowest ${1}^{\ensuremath{-}}$ states peak at $N=82$. Yield information on a few levels in $^{137}\mathrm{Ba}$ and $^{138}\mathrm{Ba}$ was also obtained.