Energy Dependence of Promptν¯for Neutron-Induced Fission ofU235

The energy dependence of ${\overline{\nu }}_p$, the average number of prompt neutrons per fission, for ${\mathrm{U}}^{235}$ has been studied over the incident neutron energy range 0.03 to 1.76 Mev by measuring the ratio of prompt neutrons from neutron-induced fission of ${\mathrm{U}}^{235}$ to those from spontaneous fission of ${\mathrm{Cf}}^{252}$. The extrapolated value at $E_n=0\mathrm{}$ has been normalized to ${\overline{\nu }}_p$ for ${\mathrm{U}}^{235}$ at thermal energies. The results have been fitted to an equation of the type ${\overline{\nu }}_p={\overline{\nu }}_p\mathrm{}\left(0\right)+a{E}_n$, where $E_n$ is the incident neutron energy in Mev, yielding ${\overline{\nu }}_p\left({\mathrm{U}}^{235}\right)=2.414+(0.097\mathrm{}\pm 0.008)E_n$. ${\overline{\nu }}_p$ for ${\mathrm{Cf}}^{252}$ spontaneous fission is 3.754±0.045.