Comparing fission-product yields from photon-induced fission of ²⁴⁰Pu and neutron-induced fission of ²³⁹Pu as a test of the Bohr hypothesis in nuclear fission

¹ Nuclear and Chemical Sciences Division, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA
² Duke University, Department of Physics, Box 90308, Durham, NC 27708-0308, USA
³ Triangle Universities Nuclear Laboratory, Durham, NC 27708, USA
⁴ Los Alamos National Laboratory, Los Alamos, NM 87545, USA

^* e-mail: silano1@llnl.gov

Published online: 28 September 2020

Abstract

Fission product yields (FPYs) are a uniquely sensitive probe of the fission process, with well established dependence on the species of nucleus undergoing fission, its excitation energy and spin. Thus FPYs are well suited for testing Bohr’s hypothesis in the context of nuclear fission, which states that the decay of a compound nucleus with a given excitation energy, spin and parity is independent of its formation. Using FPYs, we have performed a new highprecision test of the combined effects of the entrance channel, spin and parity on the fission process from two of the most commonly used particles to induce fission neutrons and photons. The ²³⁹ Pu(n,f) reaction at E_n = 4.6 MeV and the ²⁴⁰ Pu(γ,f) reaction at E_γ = 11.2 MeV were used to produce a ²⁴⁰ Pu^∗ compound nucleus with the same excitation energy. The FPYs from these two reactions were measured using quasimonoenergetic neutron beams from the TUNL’s FN tandem Van de Graaff accelerator and quasimonenergetic photon beams from the High Intensity γ-ray Source (HIγS) facility. The FPYs from these two reactions are compared quantitatively for the first time.