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

TL;DR

This study provides new absolute measurements of total kinetic energy (TKE) release in $^{239}$Pu(n,f) fission across a wide neutron energy range (2.4 to 100 MeV), clarifying previously puzzling trends at high energies.

Contribution

The paper presents the first high-energy TKE measurements for $^{239}$Pu(n,f) up to 100 MeV, resolving inconsistencies in earlier data and analyzing fission fragment mass and asymmetry.

Findings

TKE remains relatively constant from 30 to 50 MeV, contrary to earlier decreasing trends.

Measured TKE values at high neutron energies provide new insights into fission dynamics.

Discussion of fission asymmetry and fragment mass distortion enhances understanding of fission processes.

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.