Validating the Bohr Hypothesis: Measuring the Energy Evolution of Fission-product Yields from Photon-induced Fission of ²⁴⁰Pu

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 formation. High-precision measurements of the fission product yields (FPYs) of ²⁴⁰Pu using monoenergetic photons produced at the HIGS facility between 8 and 16 MeV will be performed to study the energy dependence, creating the same compound nucleus and excitation energy as neutron-induced fission of ²³⁹Pu. Prior systematic studies of neutron-induced FPYs in ²³⁵U, ²³⁸U, and ²³⁹Pu revealed a peculiar energy dependence of some high-yield FPYs: a positive slope up to about 4-5 MeV which then turns negative as the incident neutron energy increases. This low energy positive trend has been one of the challenging topics in nuclear theory, especially for low-energy fission where microscopic properties associated with the shell structure play an essential role. The first results for FPYs at E_γ=11.2 MeV will be presented, in comparison with neutron-induced FPYs for ²³⁹Pu. Implications for validating the Bohr hypothesis will be discussed.