The Use of a Gamma Ray Imaging Device for In-Cell Assay

Gamma ray imaging has become an established technique within the nuclear industry, especially within the field of decommissioning. The technique is most commonly used to identify the origins of radiation within contaminated environments in order to provide a level of characterisation that is not possible using conventional dosemeters. Gamma ray images demonstrate, in a clear, easy to understand format, where there are significant sources of gamma emitting radiation. These images are often used to help determine decontamination, decommissioning or clean-up strategies. Recent developments at Sellafield, in the UK, have demonstrated how gamma ray imaging devices can be used to perform in-cell, quantitative, assay. A data collection and analysis procedure has been developed that can be used to produce activity values for gamma bearing items. The technique is of especial value as the items of interest can be located in cells with limited or no man access, either due to poor physical access or high dose rates. This quantitative assay technique can be used to segregate wastes in-situ, allowing only wastes meeting user-specified criteria to be selected. This paper describes two successful applications of this newly developed technique on the Sellafield site. The technique is covered by European Patent - EP1315004A1 and US Patent - US7095030B2. (authors)