ABSTRACT
Geophysical methods employing radioactivity have been in use for quite some time, beginning with the application of gamma-logging in the petroleum industry, which was done as down-hole "spot" examinations and large-area aerial mapping. Traces of naturally occurring radioactive minerals are present in all igneous, sedimentary, and metamorphic rocks and in waters of the earth. Beginning in the late 1950s, nuclear techniques began to be used in marine survey and exploration tasks. These efforts, which continue today, center around three methods: natural radioactivity measurements; neutron activation prompt and delayed gamma radiation measurement, and X-ray fluorescence. From a chronological standpoint, natural radioactivity measurements were the first nuclear methods to be employed on the sea floor, with the first efforts having been done by the Russians. Since then, separate research efforts utilizing measurement of natural radioactivity have been conducted by groups in the United States and Great Britain.
