Fission-product Yields from Photon-induced Fission of ²⁴⁰Pu and Neutron-induced Fission of ²³⁹Pu as a Function of Incident Energy

The Bohr Hypothesis, one of the most fundamental assumptions in nuclear fission theory, states that the decay of a compound nucleus with a given excitation energy, spin and parity is independent of its formation¹. Using fission product yields (FPYs) as a sensitive probe, we have performed novel high-precision test of the combined effects of the entrance channel, spin and parity on the fission process. Two different reactions were used in a self-consistent manner to produce a compound ²⁴⁰Pu nucleus with the same excitation energy: neutron induced fission of ²³⁹Pu and photon-induced fission of ²⁴⁰Pu. The FPYs from these two reactions were measured using quasimonoenergetic neutron beams from the TUNL’s FN tandem Van de Graaff accelerator² and quasimonenergetic photon beams from the HIGS facility. A comparison of the FPYs from ²³⁹Pu(n,f) at E_n=1.5 and 4.6 MeV with those from ²⁴⁰Pu(γ,f) at E_γ=8 and 11.2 MeV will be presented.

¹ N. Bohr and J. A. Wheeler, “The Mechanism of Nuclear Fission.” Physical Review 56, 426 (1939).

² M.E. Gooden et al., “Energy Dependence of Fission Product Yields from ²³⁵U, ²³⁸U and ²³⁹Pu for Incident Neutron Energies Between 0.5 and 14.8 MeV.” Nuclear Data Sheets 131, 319 (2016).