Total kinetic energy and mass yields from the fast neutron-induced fission of $^{239}$Pu

Abstract

The total kinetic energy (TKE) release in fission is an important observable, constituting over 80% of the energy released in fission (E$_{f}$ $\approx$ 200 MeV). While the TKE release in the $^{239}$Pu(n,f) reaction was previously measured up to 50 MeV incident neutron energy (E$_{n}$), there were features in TKE release at the highest values of E$_{n}$ that were puzzling. There was a marked flattening of TKE release from E$_{n}$ = 30 to 50 MeV, in disagreement with the clearly decreasing TKE observed from E$_{n}$ = 0.5 to 30 MeV. To verify and clarify this trend, TKE measurements at higher values of E$_n$ were made. We present absolute measurements of TKE release in $^{239}$Pu(n,f) from E$_{n}$ = 2.4 to 100 MeV. We used silicon PIN detectors to measure the fragment energies and deduce mass-yield curves using the 2E-method. We also discuss fission asymmetry and the relationships between approximate fission fragment mass and distortion.