The advancement of a technique using principal component analysis for the non-intrusive depth profiling of radioactive contamination

A non-intrusive technique using principal component analysis, to infer the depth of the fission fragment caesium-137, when it is buried under silica sand has been described. Using energy variances within different γ-ray spectra, a complete depth model was produced for a single caesium-137 source buried under 1mm depths ranging between 5-50 mm. This was achieved using a cadmium telluride detector and a bespoke phantom. In this paper we describe the advancement of the technique by further validating it using blind tests for applications outside of the laboratory, where not only the depth (z) but also the surface (x, y) location of γ-ray emitting contamination is often poorly characterised. At present the technique has been tested at the point of maximum activity above the entrained γ-ray emitting source (where the optimal x, y location is known). This is not usually practical in poorly characterized environments where the detector cannot be conveniently placed at such an optimal location to begin with and scanning at multiple points around the region of interest is often required. Using a uniform scanning time, the point of maximum intensity can be located by sampling in terms of total count rate, and converging on this optimal point of maximum intensity.