Photofission of 238U at the energy of the giant dipole resonance

Photofission of 238 U by bremsstrahlung photons is studied at four energies of an electron accelerator: 19.5, 29.1, 48.3, and 67.7 MeV. The yields of the fission fragments after the emission of prompt neutrons are obtained using the gamma-ray spectroscopic technique. The mass distributions of photofission are obtained at different upper energies of the bremsstrahlung spectrum. The ratio the symmetric-fission mode to the asymmetric mode is obtained from the mass distribution. The symmetric mode becomes 3–4 times greater than the asymmetric as the excitation energy of the 238U nucleus increases from 12 to 16 MeV.