Slow Neutron Velocity Spectrometer Studies of H, D, F, Mg, S, Si, and Quartz

Abstract

The neutron proton cross section has been measured using a paraffin sample. The observed free proton cross section is (20.6\ifmmode\pm\else\textpm\fi{}1). The cross section-curve below 0.05 ev is well matched by a theoretical curve and approaches 4 times the free proton cross section at very low energies. The thermal cross section of ${\mathrm{D}}_{2}$O is well matched by the curve ${\ensuremath{\sigma}}_{{\mathrm{D}}_{2}\mathrm{O}}=(10+0.72{E}^{\ensuremath{-}\frac{1}{2}})$. The free cross section of D is (3.3\ifmmode\pm\else\textpm\fi{}0.2). The thermal cross section of fluorine in a fluorocarbon oil is well matched by the curve ${\ensuremath{\sigma}}_{\mathrm{F}}=(3.3+0.11{E}^{\ensuremath{-}\frac{1}{2}})$. The cross section of the free fluorine is (3.3\ifmmode\pm\else\textpm\fi{}0.5). The cross section of Mg is essentially constant at (3.4\ifmmode\pm\else\textpm\fi{}0.1) ev. No resonances are observed in Mg. Microcrystalline interference effects are noticed in the low energy region. The thermal cross section of sulfur is well matched by the curve $\ensuremath{\sigma}=(1+0.098{E}^{\ensuremath{-}\frac{1}{2}})$. No resonances are observed in S. The cross section of Si is essentially constant at (2.25\ifmmode\pm\else\textpm\fi{}0.1). No resonances are observed in Si. Microcrystalline interference effects are noticed in the low energy region. The effective neutron cross section of an optical quartz crystal decreases from the additive cross section of (9.2\ifmmode\pm\else\textpm\fi{}0.2) at \ensuremath{\sim}10 ev to 1.25 at 0.025 ev which is taken to be the residual incoherent cross section.