The Production of High Energy Neutrons by Stripping

Abstract

When a target is bombarded with high energy deuterons, a narrow beam of high energy neutrons is produced by a process in which the proton in the deuteron strikes the edge of the nucleus and is stripped off, while the neutron misses and continues on its way. The cross section for this stripping process is $\sigma =\frac{1}{2}\pi R{R}_d$, where $R$ is the nuclear radius and $R_d$ is the deuteron radius, or $\sigma =5\mathrm{}{A}^{\frac{1}{3}}\times {10}^{-26\mathrm{}}$ ${\mathrm{cm}}^2$. The yield of neutrons from a ½-in. Be target (in which the energy loss for 190-Mev deuterons is 20 Mev) is nearly 2 percent. The neutrons come out with an energy spread around $\frac{1}{2}{E}_d$ having a half-width $\Delta E_{\frac{1}{2}}=1.5\mathrm{}{\left(E_d{\epsilon }_d\right)}^{\frac{1}{2}}$. Here $E_d$ is the kinetic energy of the deuteron, ${\epsilon }_d$ its binding energy. For light nuclei the half-width of the neutron angular distribution is $\Delta {\theta }_{\frac{1}{2}}=1.6\mathrm{}{\left(\frac{{\epsilon }_d}{E_d}\right)}^{\frac{1}{2}}$. The half-width increases somewhat with atomic number, primarily because of the deflection of the deuteron by the Coulomb field as it approaches the nucleus, and, to a lesser extent, because of multiple scattering in the target. The increase in half-width from Be to U is about 25 percent. The calculated halfwidths and angular distributions agree well with the measurements of Helmholz, McMillan, and Sewell.