Attempts have been made for some time to determine the magnitudes of the individual processes of elastic scattering, inelastic scattering, radiative capture, fission, (n,2n), and other reactions which comprise the total interaction cross section of neutrons. In the energy range of 3 to 15 Mev, which is to be discussed in this paper, the predominant factors of the total cross section are those from elastic and inelastic scattering. This paper is to discuss a method of measuring directly all effects other than elastic scattering, a non-elastic cross section, which is very nearly the cross section for compound nucleus formation.