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

Photofission of 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 U nucleus increases from 12 to 16 MeV. [ABSTRACT FROM AUTHOR]