Slow Neutron Velocity Spectrometer Studies of O2, N2, A, H2, H2O, and Seven Hydrocarbons

Abstract

The slow neutron cross sections of free atoms of O, N, and A have been determined to be; O:3.73, N:9.96, A:0.68 barn. Between 1 and 15 ev the ${\mathrm{N}}_2$ curve shows an $E^{-\frac{1}{2}}$ slope of 0.34 barn×${\mathrm{}\left(\mathrm{ev}\right)\mathrm{}}^{\mathrm{½}}$ per atom. Measurements on these elements have been extended to over 10,000 ev with no resonances observed. Dependence of cross section upon neutron energy from 1 ev to 0.003 ev is presented for ${\mathrm{O}}_2$, ${\mathrm{N}}_2$, ${\mathrm{H}}_2$, ${\mathrm{H}}_2$O, methane, ethane, propane, $n$-butane, cetane, ethylene, 1,3-butadiene, and liquid$n$-butane. At the lowest energies, the large observed ${\mathrm{H}}_2$ cross section is attributed largely to thermal translational motion of the molecule. The measurements on the hydrocarbons show the effect of the binding of H in various molecules. Comparison with the theories of Bethe and Arley is made. No difference has been detected in cross-section measurements on gaseous and liquid $n$-butane.