A phantom for research studies of radiologically-contaminated land

A phantom designed for the study of radiologically-contaminated land is described. The phantom comprises a bespoke, 1 m3 outer tank and an inner tube matrix for the deployment of γ-ray emitting radioactive sources. The phantom was filled to a depth of 900mm with dry sandy loam to mimic soils found in areas surrounding nuclear legacy facilities in the U.K. A series of non-intrusive spectral measurements were taken using an automated scanning rig and a cadmium telluride γ-ray detector. The detector was clamped at a constant height above the phantom, face-down and sequenced over a pre-defined grid above the phantom, using a scanning rig. A small caesium-137 source was positioned at a depth of 150mm in one of the tubes at random. Scans were then conducted at 30 minute intervals at twelve separate measurement points, to allow sufficient counting time to isolate the γ-ray caesium-137 662 keV photopeak from the background. A CAD model was then built of a simplified albeit geometrically correct representation of the phantom and the reading points. The combination of this model and the imported γ-ray spectra has enabled the inverse modelling technique N-Visage™ to be validated against the accurate surface location for the source without prior knowledge.