The Interaction of Slow Neutrons with Nuclei

The influence of the molecular binding of the proton has been investigated by measuring the total cross section per proton, for neutrons absorbed by cadmium (C neutrons), of a series of gaseous hydrocarbons of the form ${\mathrm{C}}_n{\mathrm{H}}_{2n+2}$. The measurements were also extended to include gaseous hydrogen (${\mathrm{H}}_2$), "ordinary" water (${\mathrm{H}}_2$O), and solid paraffin. The results show that the cross section per proton increases rapidly from the value for the free proton, varying roughly as the square of the reduced mass of the system. The bound proton cross section as measured for the highest hydrocarbon (paraffin) approaches a limiting value of 2.4 times that for the free proton. The dependence of neutron scattering on structure was investigated from measurements on one of the hydrocarbons, cetane (${\mathrm{C}}_{16}$ ${\mathrm{H}}_{34}$) in its liquid and solid states. The marked increase in the cross section of the liquid state over the solid state indicates that a large amount of coherent scattering must be present. The total cross sections of the deuteron in "heavy" water (${\mathrm{D}}_2$O), and of helium, neon, argon, krypton, oxygen, and nitrogen in the gaseous state, were also measured.