252 Cf-Based Delayed-Neutron Logging System For In Situ Assa
IRT Corporation of San Diego, California, recently concluded the development of an engineering prototype delayed-neutron borehole logging system for Bendix Field Engineering Corporation , a prime contractor to the U. S. Department of Energy. The logging probe utilizes delayed-neutron activation analysis (DNAA) to determine the uranium concentration in the formation surrounding the borehole. One of the most important attractions of this technique is that it completely circumvents the problem of "disequilibrium. " A radioisotopic source containing a few hundred micrograms of 252Cf provides the neutrons for activation of formation elements. Following calibration at the DOE borehole model facility in Grand Junction, Colorado, the system was successfully operated at uranium mining and exploration sites in Texas and Wyoming. The application of the system to in situ determination of plutonium was demonstrated at the Department of Energy''s Hanford Reservation near Richland, Washington. A second 252Cf DNAAlogging system has been constructed by IRT and is now in operation providing routine logging service to the uranium industry. A novel feature of this probe is a neutron flux monitoring system which allows effective compensation of the probe response for variations in the neutron scattering and absorption properties of the formation. The principles of operation, the hardware, the calibration methods, and the results of field tests and routine operation of the new delayed neutron logging system are described and examples of logs obtained with the system are presented and interpreted.
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