Compton scatter imaging of a nuclear industry site

A low cost, lightweight Compton scatter camera has been designed and used to image an area within the BNFL Sellafield reprocessing plant in the UK. The area was a small cell (~12 m³) containing a distribution of Cs-137. The area posed a difficult problem in that camera access was very limited; just two 6 cm diameter access holes in one of the side walls. A technique has been developed whereby a cluster of detectors operating as a Compton camera is inserted into the area and positioned at relative locations calculated to provide optimum spatial resolution. A computer model has been devised to identify the optimum geometric arrangement of the three detectors forming the camera and the optimum positions of the detector cluster within the area. At each location Compton scattered spectra were recorded at two separate orientations of the camera. The measured spectra have been reconstructed to produce a 3D radiation map of the cell interior. The data set is displayed on a wireframe model of the cell. The image quality is limited but it allows images to be obtained in a difficult environment that would be inaccessible to other systems. All work has been undertaken on the behalf of BNFL for use at the Sellafield plant