Alternate Approach to the 239Pu(n,2n) Cross Section

Abstract

Using existing experimental data for neutron-induced total, elastic, inelastic, reaction and fission cross sections, as well as results from nuclear model calculations and evaluations from nuclear reaction data libraries, we derived an estimate for the cross sections for the {sup 235}U(n,2n) and {sup 239}Pu(n,2n) reactions for the neutron energy range from threshold to approximately 12 MeV. In effect, our approach is based on subtracting the fission and inelastic cross sections from the total reaction cross section where the difference is expected to yield the (n,2n) cross section. In addition to this subtraction approach, a ratio method and a differential method have also been explored. For {sup 235}U(n,2n), as a test case, we arrive at a cross section consistent with previous measurements, and for {sup 239}Pu(n,2n) we obtain a peak value of 400 {+-} 60 mb for the incident neutron energy range of 10 {le} E{sub n} {le} 12 MeV.