Abstract

The physical principles of a new method for uranium detection based on use of a pulsed source of neutrons are presented. The method employs measurement of the neutron time distributions in rock media following a burst of fast neutrons. A time- and energy-dependent (but space-independent) theory is developed for the four principal time distributions that follow production of fission neutrons by each of the two possible reactions:1. Prompt thermal fission of 235 U:a. Epithermal neutron time distribution,b. Thermal neutron time distribution.2. Delayed fission of uranium:a. Neutron time distribution due to delayed fission in 235 U,b. Neutron time distribution due to delayed fast fission in 238 U.Theoretical analysis of these phenomena leads to the conclusion that the detection of uranium in rocks is possible using either the epithermal neutron time distribution from the prompt fission of 235 U by thermal neutrons or the delayed neutron distribution from fast neutron fission of 238 U or thermal neutron fission of 235 U.Experiments performed on laboratory models of uranium ore show the feasibility of detecting fission neutrons and the validity of the theory presented in the paper. For normal borehole-logging measurements, a pulsed neutron source with an average output of about 10 9 n/sec is needed. LIST OF SYMBOLSTable Table

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