Energy Spectrum of Neutrons from Thermal Fission of U235

A proton recoil counter has been used to determine the neutron spectrum, in the energy range 3.3-17 Mev, of a beam produced by irradiating 95 percent U²³⁵ (metal) in the central experimental hole of the Los Alamos Homogeneous Reactor. Most of the fissions were induced by slow neutrons. The data are combined with those obtained by D. Hill and by T. W. Bonner, R. A. Ferrell and M. C. Rinehart; the composite spectrum so obtained extends from 0.075 to 17 Mev. Fits with two general formulas are discussed.