Moderation of Neutrons in SiO2 and CaCO3

摘要

The spatial distributions of indium resonance neutrons about a ``point'''' Ra‐Be source have been measured in pure CaCO3 (limestone) and SiO2 (sand) out to r2≈9τ. Both media show nearly Gaussian distributions corresponding to Fermi ages τ(SiO2)=1906±90 cm2 and τ(CaCO3)=461±23 cm2 over most of the range observed. Excess resonance flux near the source, more pronounced in CaCO3 than in SiO2, appears to be due to inelastic scattering although such interpretation is not unambiguous. Space integrals indicate ∼10 percent more absorption in CaCO3 than in SiO2 during moderation. Data were corrected for 4.5‐hr activity, 54‐min activation by high energy neutrons, and edge effects; consideration was given to the 3.9‐ and 9‐ev In levels in defining the mean detection energy and to the nonmonoenergetic nature of the Ra‐Be source in affecting the shape of the indium resonance spatial distribution.