## 5 Conclusions  
The main conclusions from this article boil down to the following:  
* At an economically viable flight speed, with detailed terrain draping at an altitude of the first tens of metres, it is possible to achieve a similar accuracy of gamma radiometric mapping to that of the ground survey. In cases where objects-sources of anomalies are tens to hundreds of metres in size, UAV-gamma radiometry can provide even better results with significantly higher economic efficiency. * Scintillation detectors with a volume of even 100 cubic centimetres make it possible to obtain sufficiently informative and reproducible maps of the U, Th, K-40, even in conditions of low contrast of gamma-field anomalies. To do this, it is necessary to perform UAV surveys at a constant altitude of up to several tens of metres; to use spectrometers with a sufficiently high energy resolution to separate the low-energy lines of uranium and thorium; the density of the network of survey profiles should be sufficient to overlap the 'effective radii' from at least four adjacent routes and; it is imperative to use several low energy lines in addition to the commonly used 1.76 (U) and 2.62 (Th). Local polynomial interpolation can be used to smooth out large dispersion of the measured data. It is shown that the use of only \"classical\" energy lines for uranium or thorium does not provide the possibility of obtaining reproducible maps of these radionuclides. It is shown that the best quality of geostatistical surfaces was obtained for uranium, since in this case three energy lines were used, instead of two, as for thorium. * Despite the possibility of obtaining correct spectrometric data with 100 cm\({}^{3}\) detectors, when performing gamma surveys separately from other types of geophysical survey, when there is no need to minimise the payload, it is better to use larger crystals for spectrometric surveys, from 63 \(\times\) 63 mm (in the case of CsI). The volume of such a detector is two times larger than that of those used in the experiments described, the detection efficiency of high-energy lines is noticeably higher, and therefore the survey accuracy will increase significantly. Alternatively, it is possible to increase the speed of flight slightly to improve survey productivity. The weight of the spectrometer with the CsI 63 \(\times\) 63 detector is also low and does not exceed 2 kg [16]. * For radiometric surveys, it is sufficient to use ultra-small detectors, 10-15 cm\({}^{3}\). In this case, when using SiPM, the mass of the detecting units may not exceed tens or the first hundreds of grams. * Previous conclusions indicate the possibility and good prospects of creating lightweight and compact UAV gamma systems for geological prospecting or radioecological research in radiometric and spectrometric modes, as well as fairly lightweight UAV systems for integrated geophysical survey. This further increases the economic effect of the introduction of UAV geophysics into the practice of geological exploration. * The advantage of radiometric equipment with scintillation detectors is its high availability, low cost of components, high prevalence of necessary components for spectrometers or radiometers (PMT, scintillation crystals, etc. ), as well as good knowledge of the topic up to the development of do-it-yourself (DIY) projects in gamma spectrometry. Low costs of creating measuring systems determine the high economic efficiency of the use of UAS with light scintillation detectors, since the cost of the survey directly depends on the cost of the unmanned system and the risks of its damage. This is especially important for geological applications, in which the economics of surveying is much more important than in radioecological applications. * Calibration of spectrometers required for conversion from the amount of gamma quants in the channels of radionuclides to their concentrations in the upper layer of the Earth can be performed independently, by preparing a reference site within the distribution of rocks of constant chemical composition.