Electric quadrupole giant resonance in the photofission ofU238

The ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ nucleus was studied measuring the electrofission yield and angular distributions of fission fragments, in the energy range of 5.5 to 28.3 MeV, using a new method of analysis. An $E2\mathrm{}$ isoscalar giant resonance was found in the photofission cross section of ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$. This resonance exhausts (71 ± 7)% of the energy-weighted sum rule and is located at 9.9 ± 0.2 MeV with a width of 6.8 ± 0.4 MeV. The position of this resonance is in reasonable agreement with the Bohr and Mottelson prediction ($58A^{-\frac{1}{3}}$ MeV). The width of 6.8 ± 0.4 MeV is compatible with a possible triple splitting of the resonance. From the angular distributions of photofission fragments and yield measurements of multipoles other than $E1\mathrm{}$, evidence of an $M1\mathrm{}$ mixture in the energy region 6-7 MeV was found.