Locating radiation hot spots on the ground with a gamma-ray directional sensor

This paper reports on an experimental investigation to determine the feasibility of locating radiation hot spots within an area of contamination on the ground that contains radionuclides. The detecting and locating sensor is carried in a helicopter that can rapidly scan large areas of contamination for hot spots. A scintillation type of gamma-ray directional sensor (GRDS) was used in this study. Previous work showed that a GRDS could detect and accurately locate stationary point and broad sources of gamma-rays or X-rays by rotating a GRDS in the field of radiation. In this present study, the sensor was stationary but the radiation source was moving pass the sensor. This technique simulated a helicopter flying over an area of contamination on the ground and scanning the area for hot spots with a sensor that is fixed in position on board the helicopter. The experimental approach generated data that established the operational limitations of the helicopter's speed, height, and the intensity of the hot spot relative to the GRDS's sensitivity. The results show that a GRDS sensor in a helicopter can locate cesium-137 hot spots on the ground. Hot spots with an activity of about 0.3 Ci can be located from a helicopter moving with a speed of 44.7 m/s at a height of 62.5 m.