Remote alpha imaging in nuclear installations: new results and prospects

Abstract

For more than ten years the CEA has been using gamma imaging systems for radiological characterization purposes during decommissioning operations. This technology is very effective for detecting high-energy gamma emitters, but less so for characterizing actinides, which are mainly alpha emitters. In order to provide a full range of decommissioning tools, the gamma-cameras were supplemented by another imaging system capable of generating images directly from alpha emissions. This paper describes the initial laboratory and field test results obtained with a prototype camera capable of displaying alpha radioactivity. The system is based on the detection of ultraviolet radiation emitted by nitrogen when irradiated by alpha particles. The alpha contamination is localized by superimposing it on a visible-light image. All measurements must be carried out in complete darkness. Laboratory tests showed that the system is capable of detecting point sources and extended sources at levels as low as 430 Bqmiddotcm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> . Profile measurements of point sources revealed a scintillation bubble with dimensions corresponding to the range of alpha particles in air. The device is also capable of detecting the phenomenon through translucent materials such as glove box panels. The camera has been implemented for in situ examination of various fuel cycle facilities, and under these conditions has revealed alpha contamination without any breach of containment through several millimeters of plexiglas