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

M. Caner, M. Segev, S. Yiftah

Nuclear Science and Engineering

Volume 59 / Number 4 / April 1976 / Pages 395-405


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A consistent compound nucleus theory of (n, 2n) and (n, 3n) neutron emission was applied to 238U to obtain the energy spectra of the second and third secondary neutrons. The evaluation was based on inelastic level excitation and evaporation data for 238U, 237U, and 236U. The 238U and 236U data were retrieved from ENDF/B-IV files; the 237U data were evaluated in the Soreq Nuclear Research Center using experimental information and statistical reaction theory codes. At reaction energies E0 just above the (n, 2n) threshold energy B2, the energy E of the second inelastic neutron has a spectrum of (E0 - B2 - E); above the (n, 3n) threshold, B3, the third neutron energy has a spectrum of (E0 - B2 - E)3. At energies E0, high above the thresholds, the second and third neutron spectra approach the evaporation form. A secondary neutron spectrum for any given reaction energy E0 is approximated by a composite form where i = 2, 3 for the second and third neutrons, respectively. The temperatures Ti and blending coefficients βi were evaluated for several energies in the range from threshold up to 15 MeV.

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