Thermal-neutron intensities in soils irradiated by fast neutrons from point sources

Thermal-neutron fluences in soil are reported for selected fast-neutron sources, selected soil types, and selected irradiation geometries. Sources include 14 MeV neutrons from accelerators, neutrons from spontaneously fissioning 252Cf, and neutrons produced from alpha-particle interactions in the 241Am/Be source. Soils are of five types, ranging from a dry porous soil to a wet dense soil. Neutron fluences are reported for sources above the soil surface and positioned at selected depths below the soil surface. Methods are demonstrated for incorporating thermal-neutron fluence data into the deconvolution of capture gamma-ray spectral data in the method of assessing soil contamination using prompt gamma-ray neutron activation analysis.