| Summary: | The lack of calibration to a wide range of well conditions has limited the application of the University of Arizona’s neutron instruments. The calibration is necessary before quantitative results may be obtained. A survey of the literature on the neutron method is presented from petroleum industry, soil science, and groundwater hydrology sources. A controlled system, consisting of nine well casings in a homogeneous unconsolidated medium, was constructed, for the study. Two neutron-neutron instruments equipped with Am-Be sources of lOO-mc (millicurie) and 3-c (curie) strength, were operated in the system. Data was collected under saturated and water-table conditions to determine the quantitative reaction and the qualitative discrimination of the instruments to the range of variables encountered in well design. The diameter and composition of well casing and the position of the neutron probe in the casing were found to be important factors in neutron logging. The largest diameter of casing in which the 100-mo instrument can be applied was found to be 4 inches. The 3-c instrument was effective in casings as large as 16 inches in diameter. The calibration relationship between moisture content and chart deflection for the 3-c instrument was defined for one value of moisture content.
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