Nuclear resonance fluorescence inBa136

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° and 126°, 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 $1^{-}$ assignment and a value ${\Gamma }_0=88\mathrm{}\pm 22$ meV for the partial width of the ground state transition. The corresponding $E1\mathrm{}$ strength is approximately $\frac{1}{3}$ of the $E1\mathrm{}$ strengths observed for the strongest low-lying $E1\mathrm{}$ transitions in the even-even $N=82\mathrm{}$ nuclei. When combined with previous observations for $N>\mathrm{}82\mathrm{}$, the result obtained for ${}_{}{}^{136}{}_{}{}^{}\mathrm{Ba}$ ($N=80\mathrm{}$) indicates that the strengths of the ground state transitions from the lowest $1^{-}$ states peak at $N=82\mathrm{}$. Yield information on a few levels in ${}_{}{}^{137}{}_{}{}^{}\mathrm{Ba}$ and ${}_{}{}^{138}{}_{}{}^{}\mathrm{Ba}$ was also obtained.