Dipole Strength in the 235U(gamma,gamma') Reaction up to 2.8 MeV

Spectra of the $^{235}\mathrm{U}$($\ensuremath{\gamma},{\ensuremath{\gamma}}^{\ensuremath{'}}$) reaction were measured at the S-DALINAC at bremsstrahlung end-point energies ${E}_{0}=3.5$ and $4.4$ MeV and scattering angles of ${90}^{\ifmmode^\circ\else\textdegree\fi{}}$ and ${135}^{\ifmmode^\circ\else\textdegree\fi{}}$ with respect to the beam axis. Discrete transitions are observed at excitation energies below $2.3$ MeV only. The deduced cross sections are in rough agreement with the findings of Bertozzi et al. [Phys. Rev. C 78, 041601(R) (2008)] except for the most prominent transition, where the present result is lower by a factor of about $2$. Evidence for unresolved dipole strength is found in the spectra by means of a fluctuation analysis, which was carried out up to an excitation energy of $2.8$ MeV. If this unresolved strength exhibits the same ratio of $E1/M1$ cross sections as observed in the even-mass neighbor $^{236}\mathrm{U}$, then the energy centroid ${\overline{E}}_{x}=2.5(3)$ MeV and total strength $\ensuremath{\sum}B(M1)\ensuremath{\uparrow}=3.6(1.3){\ensuremath{\mu}}_{N}^{2}$ of the $M1$ part are in good agreement with the systematics of the scissors mode in even-even actinide nuclei.