Total kinetic energy release in the fast neutron-induced fission of $^{235}$U

TL;DR

This study measured the total kinetic energy release in neutron-induced fission of uranium-235 across a wide neutron energy range, revealing a non-linear decrease linked to changes in fission modes.

Contribution

The paper provides new experimental data on TKE in $^{235}$U(n,f) reactions from 2 to 100 MeV, and analyzes the energy dependence using the Brosa fission model.

Findings

TKE decreases from 169.0 MeV to 161.4 MeV as neutron energy increases.

The TKE distribution's standard deviation remains constant between 20-90 MeV.

The decrease in TKE is due to increased symmetric fission at higher energies.

Abstract

We have measured the total kinetic energy (TKE) release for the $^{235}$U(n,f) reaction for $E_{n}$=2-100 MeV using the 2E method with an array of Si PIN diode detectors. The neutron energies were determined by time of flight measurements using the white spectrum neutron beam at the LANSCE facility. (To calibrate the apparatus, the TKE release for $^{235}$U(n$_{th}$,f) was also measured using a thermal neutron beam from the OSU TRIGA reactor). The TKE decreases non-linearly from 169.0 MeV to 161.4 MeV for $E_{n}$=2-90 MeV. The standard deviation of the TKE distribution is constant from $E_{n}$=20-90 MeV. Comparison of the data with the multi-modal fission model of Brosa indicates the TKE decrease is a consequence of the growth of symmetric fission and the corresponding decrease of asymmetric fission with increasing neutron energy. The average TKE associated with the Brosa superlong, standard I and standard II modes for a given mass is independent of neutron energy.