NEUTRON SCATTERING AND SOIL MOISTURE

Thesis/Dissertation · Mon Jan 01 04:00:00 EST 1962

OSTI ID:4772236

Fisher, Jr, C P

The history and the state of the art of moisture content and unit weight measurement in sotl by radiation techniques is reviewed and an examination made of the errors to be expected when using the various types of nuclear devices as compared to errors reported by others for tests using conventional techniques. No satisfactory mathematical solution was found from available theory describing the distribution of neutrons about a point source in hydrogeneous media. However, measured distributions available from the work of another investigator are used to show (1) that sandwater and carbon-water systems form boundary conditions that include all soil minerals and (2) the maximum possible effect on measured moisture content due to soil mineral type is approximately 10 percent of the measured value. The equipment used in this investigation did not detect the effect produced when the hydrogen in water changed its state of chemical bonding in the hydration of gypsum plaster. A thermal neutron beam generator that utilized a Ra--8e or Pu-- Be source of fast neutrons was constracted and a technique for measuring the total thermal neutron cross section of thin samples developed. The attenuation of the neutron beam followed the law I/I/sub 0/ = e/ sup - mu t/. For water the measured cross section was approximately the same as computed by summing cross sections of hydrogen and oxygen. For paraffin wax the measured cross section was appreciably larger than the sum of component values. A similar relationship was found for soils, the difference increasing directly with bound water content of the soil. Chemical analyses of a number of soils were tabulated from the literature and the weight of water of equal thermalizing power calculated, The water equivalent could be approximated by a constant plus the value of the loss-onignltion in percent by weight. For the soils tested this value of water equivalent appeared to yield a better estimate of measured total cross section than the value computed by summing the cross sections of the atomic constituents of the soil. It was concluded (1) the total thermal neutron cross section of soil minerals could be approximated by the equation, sigma /sub total/ = 0.0445 (gram molecular weight)(3.4 + loss-on-ignition in percent) barns per molecule; (2) the effect of soil mineral type on the neutron method of soil moisture content measurement might be neglected thus making a single calibration curve suitable for use on all soils except those containing strong neutron absorbers; and (3) the present neutron moisture meters are not suitable for the investigation of the progress of hydration reactions but can be used to measure the total hydrogen content of hydrated materials. Suggestions for further research in this and allied fields are presented. A technical glossary is provided, and appendices discuss the radiation hazard associated with the use of moisture and unit weight devices; describe currently available commercial equipment; and suggest a statistically valid technique for measuring the total state of moisture content or unit weight in a compacted earth structure. (Dissertation Abstr., 23: No. 3, 1962)

• Research Organization: Originating Research Org. not identified
• NSA Number: NSA-17-001414
• OSTI ID: 4772236
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

ABSORPTION
BERYLLIUM
BIBLIOGRAPHY
BINDING ENERGY
CALCIUM SULFATES
CHEMISTRY
CROSS SECTIONS
DIAGRAMS
FAST NEUTRONS
GYPSUM
HYDROGEN
LABORATORY EQUIPMENT
NEUTRON BEAMS
NEUTRON SOURCES
PARAFFIN
PLUTONIUM
QUALITATIVE ANALYSIS
RADIUM
STATISTICS
TABLES
THERMAL NEUTRONS
WATER
WEIGHT