Integrated dose-rate mapping and hotspot localization with a UAV-mounted coded-aperture gamma camera

Rapid remote radiation monitoring is important for identifying contaminated regions while reducing personnel exposure. This study developed an unmanned aerial radiation monitoring system (UARMS) equipped with a coded-aperture gamma camera and evaluated a staged workflow integrating flight-based spatial screening with hovering-based gamma-ray imaging. A controlled outdoor experiment was conducted using 60 Co and 137 Cs point sources. The flight-based survey identified two candidate source-related regions, and the corresponding region-of-interest spectra showed photopeaks of the two sources. The UARMS and ground-based backpack surveys showed broadly corresponding spatial patterns, although their relative intensities and spatial extents differed. During hovering measurements, gamma-ray images corresponding to the two source directions were reconstructed, and ambient dose equivalent rates were estimated. A comparison of altitude-only, image-derived, and UAV-GNSS-referenced distance corrections showed that the horizontal source offset affected the estimates but did not consistently improve agreement with the theoretical source-only values for both sources. These results demonstrate the field feasibility of sequentially performing spatial screening, radionuclide identification, hotspot localization, and ambient dose equivalent rate estimation using a single coded-aperture gamma camera under controlled point-source conditions.