Excitation energy dependence of the total kinetic energy release in ${}^{235}U$$(n$,$f)$

The total kinetic energy release in the neutron induced fission of ${}^{235}U$ was measured (using white spectrum neutrons from the Los Alamos Neutron Science Center) for neutron energies from $E_n=3.2$–50 MeV. In this energy range the average post-neutron total kinetic energy $(E_{\mathrm{TKE}}$) release drops from $167.4\pm 0.7$ to $162.1\pm 0.8$ MeV, exhibiting a local dip near the second chance fission threshold. The values and the slope of the $E_{\mathrm{TKE}}$ vs $E_n$ agree with previous measurements but disagree (in magnitude) with systematics. The variances of the $E_{\mathrm{TKE}}$ distributions are larger than expected; and apart from the structure near the second chance fission threshold, the distributions are invariant for the neutron energy range from 11 to 50 MeV. We also report the dependence of the total excitation energy in fission $(E_{\mathrm{TXE}}$) on neutron energy.

Figure 1

Calculated neutron spectrum in the 15R beam area [11]. To convert the ordinate to units of neutrons/second, one must multiply the plotted values by the solid angle (sr) of the fission target, the proton beam intensity, and the width of the neutron energy bin (MeV).

Figure 2

$E_{\mathrm{TKE}}$ release data for ${}^{235}U$$(n,f$).

Figure 3

Typical $E_{\mathrm{TKE}}$ distributions for ${}^{235}U$$(n,f$).

Figure 4

Variance of the $E_{\mathrm{TKE}}$ distribution data for ${}^{235}U$$(n,f$).

Figure 5

$E_{\mathrm{TXE}}$ data for ${}^{235}U$$(n,f$).