Fission fragment γ-ray anisotropies

The anisotropy of fission fragment γ-rays in the reactions ²³⁹Pu(n_th, f) and ²³³U(n_th, f) have been measured. In this work, two γ energy bands were used to confirm the energy independence of the anisotropy. For the γ energy band of 0.49–0.65 MeV and the γ energy band of 0.83–0.92 MeV the anisotropies were found to be 0.18 ± 0.03, 0.13 ± 0.03 and 0.19 ± 0.03, 0.11 ± 0.03 for the ²³⁹Pu and ²³³U targets respectively. The data are corrected for the Doppler effect and the time of flight was large enough to eliminate the counting of neutrons. Comparisons with the theories of Nix and Swiatecki, and Strutinsky have been made and approximate correction for fragment rotation along fission axis made.