The spontaneous fission neutron spectrum of ${\mathrm{Cf}}^{252}$ from 0.2 to 7.0 Mev has been measured. Time-of-flight techniques were employed to determine the lower energy portion of the spectrum while proton recoils in emulsions were used to study the higher energy neutrons. The measured neutron spectrum is, within the experimental accuracy, described by the empirical relation $N\left(E\right)\mathrm{}\propto \exp [-0.88E(\mathrm{Mev}\left)\right]sinh{\left[2.0E\right(\mathrm{Mev}\left)\right]}^{\frac{1}{2}}$, where $N\left(E\right)\mathrm{}$ is the number of neutrons of energy $E$ per unit energy interval. The experimental results are compared with the theoretically determined ${\mathrm{Cf}}^{252}$ fission neutron spectrum.

• Received 10 July 1957

DOI:https://doi.org/10.1103/PhysRev.108.411