Estimating the depth of embedded contaminants from in-situ gamma spectroscopic measurements

The depth of radiological contamination is information required for decontamination and decommissioning of nuclear facilities. This paper proposes and tests a simple technique for measuring the depth of contamination. The method uses measurements with an HPGe detector at two distances (or heights) from the surface on the same side of the medium. The ratio of the photopeak areas easily can be used to yield the depth of an embedded source. The calculational algorithm was verified by simulations with the MCNP4C code and laboratory experiments for a point source and other special sources. Predictions of the depth for shallowly embedded sources have relatively large uncertainties (approximately 18%) but improve as depth increases. This technique provides a very easy way for a user to quickly estimate the depth of the subsurface contamination on site.