A Fast Method for Modelling A Gamma-Ray Field over Inhomogeneous Ground Sources

Designing airborne gamma-ray surveys for geological purposes, mineral prospecting, environmental applications or radioactive contamination mapping requires the optimal choice of survey parameters such as the survey altitude, line spacing and survey speed with respect to the sensitivity of the instruments employed and the presumed size and intensity of the detected anomalies. The gamma-ray field attenuates significantly with the distance from the source; being able to model gamma-ray field intensity in various detector positions can be very useful. In recent years, the use of mini-airborne UAV radiometric measurement has developed rapidly. On the one hand, the low payload capacity of UAV results in low sensitivity of the employed detectors; the possibility of increasing gamma-ray signals from low altitude surveys and low speeds on the other hand raises the demand for simulating the gamma-ray field of local inhomogeneous radiometric anomalies. The gamma-ray field modelling method introduced in this paper is based on the monoenergetic approach and discretization of geological radioactive sources utilizing a three-dimensional net of point sources. The optimal density of point sources depends on the detection altitude and the degree of inhomogeneity of the radioactive source. The designed modelling method was verified by comparing the model data with experimental data from three localities where uranium anomalies occur. The degree of conformity of the model and experimental data is acceptable and confirms the applicability of the modelling method. The paper describes a relatively fast and simple gamma-ray field modelling method that is appropriate for ground planar radioactive anomalies. The method is useful for designing survey parameters and for interpretation of detected airborne gamma-ray anomalies.