Fission Neutron Spectrum ofU235

The neutron spectrum associated with the fission of ${\mathrm{U}}^{235}$ induced by slow neutrons has been remeasured from 0.18 to 12 Mev. Two different experimental techniques were employed in this measurement: (1) the time-of-flight method covering the energy range from 0.18 to 2.7 Mev, and (2) the photographic plate method encompassing the energy range from 0.35 to 12 Mev. The combined results of these measurements fit the relation, $N\left(E\right)=K{e}^{-\frac{E}{0.965}}sinh\left[{\mathrm{}(2.29E)\mathrm{}}^{\frac{1}{2}}\right]$, where $N\left(E\right)\mathrm{}$ is the neutron flux, $E$ is the neutron energy in Mev and $K$ is a constant. The simpler expression, $N\left(E\right)=K{E}^{\frac{1}{2}}{e}^{-0.775E}$, also fits the data well for neutron energies below 9 Mev.