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Title: Investigation of the response of a neutron moisture meter using a multigroup, two-dimensional diffusion theory code.
Authors: Ritchie, AIM
Wilson, DJ
Keywords: Two-dimensional calculations
Moisture gages
Issue Date: Dec-1984
Publisher: Australian Atomic Energy Commission
Citation: Ritchie, A. I. M., & Wilson, D. J. (1984). Investigation of the response of a neutron moisture meter using a multigroup, two-dimensional diffusion theory code. (AAEC/E579). Lucas Heights, NSW: Australian Atomic Energy Commission.
Abstract: A multigroup diffusion code has been used to predict the count rate from a neutron moisture meter for a range of values of soil water content ω thermal neutron absorption cross section Sα (defined as SIGMA Σα/ρ) of the soil matrix and soil matrix density ρ two dimensions adequately approximated the geometry of the source detector and soil surrounding the detector. Seven energy groups the data for which were condensed from 128 group data set over the neutron energy spectrum appropriate to the soil-water mixture under study proved adequate to describe neutron slowing-down and diffusion. The soil-water mixture was an SiO2-water mixture with the absorption cross section of SiO2 increased to cover the range of SIGMA Σα required. The response to changes in matrix density is in general linear but the response to changes in water content is not linear over the range of parameter values investigated. Tabular results are presented which allow interpolation of the response for a particular ω, Sα and ρ. It is shown that R(ω.Sα. ρ)= ρ M(Sα) + C (ω)is a crude representation of the response over a very limited range of variation of ω and Sα. As the response is a slowly varying function of ρ, Sα, and ω a polynomial fit will provide a better estimate of the response for values of ρ, Sα and ω not tabulated.
Gov't Doc #: 969
ISBN: 0642597979
Appears in Collections:Scientific and Technical Reports

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