Determination of the Probing Distance in Pulsed-Neutron Uranium Logging Experiments

The operation of pulsed-neutron uranium logging systems is clarified through the derivation of a theoretical expression that shows the relative detector output attributable to rock at different distances from the detector. The results of numerical neutron transport calculations are used to evaluate this expression. Although the theory considered here is applicable to several nuclear logging methods, we restrict our attention to an examination of the prompt fission neutron method. Results show that, depending on the water content of the rock matrix, significant contributions to the detector output are caused by ore-bearing rock as far as 0.3 to 0.5 m from the detector.