Angular distribution of Pu-239 photofission fragments near threshold, using neutron capture gamma rays

The angular distribution of Pu-239 photofission fragments produced by thermal neutron capture gamma rays in two targets placed in the IEA-R1 (Instituto de Energia Atomica-Reator 1) research reactor were measured. Angular distributions of the form W(θ) = A + B sin2θ were observed for discrete excitation energies of 5.43 MeV (sulphur target) and 7.35 MeV (lead target). An anisotropy that corresponds to (B/A = −0.122 ± 0.036) was recorded for E = 5.43 MeV. The angular distribution for E = 7.35 MeV was practically isotropic: (B/A = −0.01 ± 0.02).