Energy Spectra of Secondary Neutrons from the 238U(n, 2n) and (n, 3n) Reactions

Abstract

A consistent compound nucleus theory of (n,2n) and (n,3n) neutron emission was applied to $sup 238$U to obtain the energy spectra of the second and third secondary neutrons. The evaluation was based on inelastic level excitation and evaporation data for $sup 238$U, $sup 237$U, and $sup 236$U. The $sup 238$U and $sup 236$U data were retrieved from ENDF/B-IV files; the $sup 237$U data were evaluated in the Soreq Nuclear Research Center using experimental information and statistical reaction theory codes. At reaction energies E$sub 0$ just above the (n,2n) threshold energy B$sub 2$, the energy E of the second inelastic neutron has a spectrum of (E$sub 0$ - B$sub 2$ - E); above the (n,3n) threshold, B$sub 3$, the third neutron energy has a spectrum of (E$sub 0$ - B$sub 2$ - E)$sup 3$. At energies E$sub 0$, high above the thresholds, the second and third neutron spectra approach the evaporation form. A secondary neutron spectrum for any given reaction energy E$sub 0$ is approximated by a composite form for which the temperatures and blending coefficients were evaluated for several energies in the range from threshold up to 15 MeV. 6 figures, 3 tables. (auth)