Electric quadrupole giant resonance in the photofission ofU238

Abstract

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 $E2$ isoscalar giant resonance was found in the photofission cross section of $^{238}\mathrm{U}$. This resonance exhausts (71 \ifmmode\pm\else\textpm\fi{} 7)% of the energy-weighted sum rule and is located at 9.9 \ifmmode\pm\else\textpm\fi{} 0.2 MeV with a width of 6.8 \ifmmode\pm\else\textpm\fi{} 0.4 MeV. The position of this resonance is in reasonable agreement with the Bohr and Mottelson prediction ($58{A}^{\ensuremath{-}\frac{1}{3}}$ MeV). The width of 6.8 \ifmmode\pm\else\textpm\fi{} 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 $E1$, evidence of an $M1$ mixture in the energy region 6-7 MeV was found.NUCLEAR REACTIONS, FISSION Electrofission of $^{238}\mathrm{U}$ ($e, e'f$), ${E}_{0}=5.5 \mathrm{to} 28.3$ MeV, measured electrofission yield and angular distributions of fission fragments. Deduced $E2$ cross section and $E2$ isoscalar giant resonance parameters.