Cross Sections for the (n, 2n) Reaction inN14,P31,Cu63, andPr141

The ($n, 2n$) cross sections have been measured for ${\mathrm{N}}^{14}$, ${\mathrm{P}}^{31}$, ${\mathrm{Cu}}^{63}$, and ${\mathrm{Pr}}^{141}$, for neutron energies from 12.5 to 18 Mev. The annihilation radiation emitted from the product nuclides was counted with two NaI(Tl) crystals in coincidence. In the energy range measured, the cross sections were found to vary, as follows: ${\mathrm{N}}^{14}$, 3.03 to 11.67 mb; ${\mathrm{P}}^{31}$, 0 to 74 mb; ${\mathrm{Cu}}^{63}$, 186 to 836 mb; ${\mathrm{Pr}}^{141}$, 1231 to 1737 mb. The results are generally in agreement with those of others. The data are compared with curves plotted from Weisskopf's theoretical expression for ($n, 2n$) cross sections.