Aerial gamma-ray survey
AERIAL GAMMA-RAY SURVEY (EN: aerial gamma-ray survey; DE: Gammaluftbildaufnahme; FR: photographie aerienne radiographique, photographie aérienne à rayons gamma, ES: levantamiento aereo por rayos gamma; RU: аэрогаммасъемка) is the method for the measurement from the air of the intensity of the gamma radiation of the radioactive rocks. It is used for the searches for the deposits of the useful minerals. The first aerial gamma-ray survey has been conducted within the USSR during the 1946.
The aerial gamma-ray survey comprises the measurement, with the help of the multichannel spectrometer, of the intensity of the field of the gamma-radiation (within the non-overlapping ranges of the spectrum) with characteristic lines of the major isotopes within the radioactive series of uranium, thorium, and potassium: 214Bi (1.12 and 1.76 MeV), 208Th (2.62 MeV), 40K (1.46 MeV). The intensity within each range of the spectrum depends on the concentration of the radioactive elements (RAE) within the rocks, area of their halos, thickness of the non-radioactive cover of the loose rocks, relative altitude of the flight above the terrain, content of radon within the air, and also on the level of the radioactive contamination of the aircraft and cosmic radiation. Gamma radiation is absorbed by the layer of the rocks with the thickness of 1.0-2.0 metres, or by the layer of the air with the thickness of 200-300 metres, because of this the aerial gamma-ray survey is performed at the low altitudes (at most 75 metres) according to the system of the straight routes with the "matching" of the relief. Within the complicated mountainous regions, it is conducted with the curved routes along the horizontals of the relief.
They conduct the aerial gamma-ray survey together with the aero-magnetic, aero-electrical explorative, and sometimes infrared surveys. They determine the location of the aircraft (helicopter) with the method of the photographing of the terrain or with the help of the radio-geodesic navigation systems. The processing of the information requires the correction of the influence of the changes of altitude, smoothing of the results of the measurement, taking into account of the background radiation, calculation of the content of the RAE, and so on. The aerial gamma-ray survey is used for the searches for the deposits of the ores of uranium, non-ferrous metals, phosphorites, the forming of which is associated by the commonality of the migration and accumulation of the ore elements and RAE.
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