(D,T) Neutron Activation Logging

Abstract The theory of activation logging with an accelerator-type neutron source as a generator of neutrons by the deuteriumtritium (D,T) reaction is briefly reviewed and the instrumentation is described which has been employed recently in tests in field wells. Factors affecting the ability of the oxygen log to identify oil in situ are discussed both from the standpoint of instrumentation requirements and. with regard to borehole conditions and operating procedures. Examples of field logging results are given and compared with the expected results based on theory and on laboratory experiments. The role of borehole fluid in the logging process is explained, and the method of determining the optimum logging speed is discussed. Recent experience with the accelerator neutron source and instrumentation for activation logging is summarized and problems relating to the future applications for this equipment are presented. New nuclear logs which can be run in conjunction with the oxygen log are described and the advantages of a 14 Mev neutron source for conventional neutron logging are explained. Introduction Although activation logging was first proposed nearly 20 years ago the method has been of little more than academic interest until recent years due to the instrumentation difficulties involved. Apparatus has now been developed which is capable of making logs of this type and a field test of the equipment has been underway for several months. In view of the success attained to date it is confidently expected that activation logs of commercial quality will soon become available. The present paper is intended as an introduction to the operating principles of the logging equipment and a preliminary report on the results of logging tests. "Activation Analysis" is the term which has been used, since the development of the chain reacting pile, to denote the very sensitive analytical technique for detecting trace elements in samples by means of neutron irradiation. To analyze a sample of material by this technique it is placed in an atomic pile where it is irradiated by an intense flux of neutrons, after which it is removed and examined by various techniques to determine what "activation" was induced by the irradiation. Most of the earth's elements can be made radioactive by pile bombardment, and even very tiny quantities of certain elements may become sufficiently radioactive that their characteristic radiation, which may be beta rays, positrons, or gamma rays can often be identified with ease, particularly if the sample is dissolved and chemically separated into fractions.