## 2 Materials and Methods  
### Brief Description of the Gamma-Ray Geophysical Prospecting Method  
Gamma-ray prospecting--is a radiometric survey, based on measurement of natural radioactive background of rocks and ores, or radioactive contamination. Natural earth material radioactivity is caused by the presence of radioactive elements of uranium, thorium, and potassium-40 unstable isotopes. Mineral radioactivity is characterized by the activity--the number of decays per unit of time. The greater the mass fraction of radioactive elements, the greater the activity per unit mass. Thus, the total gamma radiation intensity, which is proportional to the activity, can determine the presence and estimate the content of radioactive elements in rocks. Analyzing the radiation spectral characteristics (energy spectrum), it is possible to determine the content of each of the radionuclides separately. The radioactive elements content in the composition of subsurface rocks varies very widely. Pyrogenic minerals are characterized by the highest radioactivity, the lowest radioactivity is in sedimentary rocks, and metamorphics are intermediate. However, this is only a general rule, for example, sedimentary terrigenous sand-clay rocks well sorb thorium and uranium, and therefore can be very radioactive.  
A gamma-ray survey is an effective and fairly versatile geophysical method. In geological tasks, it is used to prospect for deposits of radioactive ores; precious and basic metals, magnetically associated with radioactive elements; hydrocarbons; and, most importantly, in geological mapping. In the radioecological version, it is used to create maps of area radiation pollution.  
According to the registration methods, there is a distinction between a gamma-ray survey for general radiation using radiometers and a spectrometric survey with spectrometers, when the radiation is recorded in the optimal parts of the spectrum of the determined elements. Unlike other methods of geophysical survey, gamma-ray measurements are probabilistic, since this is the nature of radioactive decay. It is possible to increase the efficiency of gamma radiation detection when using scintillation detectors (which are the subject of this article) by increasing their size so that a larger detector receives a larger number of gamma quanta per unit of time.  
Traditionally, gamma-surveys were carried out in pedestrian, aero, and auto variants. At the same time, various radiometric equipment corresponding to the measurement method was used. In the pedestrian version, the survey is usually carried out on a regular grid of profiles and pickets, and both radiometric and spectrometric measurements are performed with the operator stopping at the points. This makes it possible to perform spectrometric measurements for several minutes or even tens of minutes, which allows the use of small-sized scintillation detectors since increasing the exposure time allows to accumulate a representative gamma spectrum. Aerogamma with the representation of the data obtained are considered the most perfect because when you remove the detector from the Earth the fixed gamma radiation is not in a single point (in fact a few kilograms of the soil or rock), but the average radiation with a certain square. At the same time, gamma radiation is absorbed by matter, including air, and its intensity quickly decreases with altitude, so due to the need for a set of statistically correct data volumes and high flight speeds of conventional aircraft, traditional aerogamma spectrometers often have several detection units with a volume of tens or even hundreds of liters. A new variant, UAV surveys, makes it impossible to effectively carry out according to classical methods, and therefore it is necessary to develop new survey methods and equipment that fully implements the advantages of UAVs. A variant of such a solution, all its main technical and methodological positions, is described in this article.