( n , 2 n ) Cross Sections for U 238 and Np 237 in the Region of 14 MeV

The cross sections for formation of $^{237}\mathrm{U}$ from $^{238}\mathrm{U}$ and for the eventual formation of $^{236}\mathrm{Pu}$ from $^{237}\mathrm{Np}$ by the ($n,2n$) reaction were measured relative to the $^{27}\mathrm{Al}(n,\ensuremath{\alpha})^{24}\mathrm{Na}$ cross section. Neutrons were produced by the irradiation of titanium tritide targets with 400-keV deuterons on the Livermore insulated core transformer (ICT) neutron generator. The determinations covered the neutron energy range from 13.7 to 14.9 MeV. From the partial cross section for $^{236}\mathrm{Pu}$ formation, the cross section was calculated for the $^{237}\mathrm{Np}$ total ($n,2n$) reaction, including the branch leading to $^{236}\mathrm{Np}^{m}$.