Radiometric Prospecting

a set of techniques in exploratory geophysics that utilize manifestations of natural radioactivity to search for and analyze ores of radioactive elements. Coupled with other techniques, radiometric prospecting is also used to search for and analyze nonradioactive ores (phosphorites, rare earths, zirconium, vanadium) that contain admixtures of radioactive elements. Radiometric prospecting is used as an auxiliary method in geological mapping.

The techniques of radiometric prospecting are based on the recording of ionizing radiation by means of ionization chambers, gas-discharge (Geiger) and crystal counters, and other nuclear radiation detectors. The measurements establish the source of radioactivity and the average content of radioactive elements in rocks, ores, water, soil, the vegetative cover, and the ground layer of the atmosphere. Measurements are affected by the concentrations of radioactive elements, the density and composition of rocks and ores, and the magnitude of the natural background of radioactivity.

Emanation techniques and methods based on the recording of gamma radiation are most commonly used in radiometric prospecting. Gamma-spectroscopic surveying and gamma prospecting carried out by aircraft, motor vehicle, or on foot are used to study radiation fields and to detect accumulations of radioactive elements. Gamma surveys of underground workings are used in analyzing fields of radioactive ores in order to better understand the structure of ore bodies. The average content of radioactive elements is assessed on the basis of results of gamma-ray probing of ores in beds and chipped masses. Radioactivity logging is carried out to provide lithologic division of sections of boreholes and to single out intervals with a higher content of radioactive elements. When deposits of uranium, thorium, and potassium salts are being analyzed, gamma-ray logging is the main method of probing boreholes.

Emanation methods of radiometric prospecting are based on measurements of the concentrations in soil atmosphere of such radioactive gases as radon (²²²Rn), thoron (²²⁰Rn), and actinon (^2l9Rn). Advances in gamma spectroscopy are causing emanation methods gradually to lose their leading role in surveying and prospecting. Radiometric prospecting also includes prospecting for uranium deposits on the basis of the aureoles of radioactive elements in subterranean waters, soils, and the vegetative cover.

The techniques of radiometric prospecting were first developed between 1922 and 1924 in Germany and the USSR. V. I. Baranov, G. V. Gorshkov, A. G. Grammakov, A. P. Kirikov, A. K. Ovchinnikov, and V. L. Shashkin are among the Soviet scientists who played a decisive role in the development and advancement of radiometric prospecting.