The use of UAVs to map ionising radiation resulting from radioactive decay is gaining popularity among researchers due to its efficiency and safety. Many studies have been conducted, most of them using expensive sensors. The present research aims to investigate the applicability of an affordable radiation detector in areas where anomalies from natural sources occur. In this research, we use a DJI Matrice 210 V2 RTK quadcopter equipped with a cost-effective Safecast bGeigie Nano Kit radiation sensor to take measurements at different altitudes above ground. We convert these data into GIS-compatible formats and produce accurate isoline maps using the Minimum Curvature interpolation technique. The results show that while the radiation intensity decreases with height, the anomaly was visible but less detailed at all heights investigated. In addition, the study highlights the significant differences in position measurements between RTK GNSS and autonomous GNSS measurements that affect the accuracy of the data. The results will contribute to a more accurate determination of the radiation extent and, thus, to maintaining safety, as well as assisting in emergency surveys and environmental monitoring.