The Radioactivity Depth Analysis Tool (RADPAT).

Shippen, B. A. and Joyce, Malcolm J. (2009) The Radioactivity Depth Analysis Tool (RADPAT). In: ASME 2009 12th International Conference on Environmental Remediation and Radioactive Waste Management (ICEM2009) :. American Society of Mechanical Engineers, 2 . American Society of Mechanical Engineers, pp. 149-155. ISBN 9780791844076 0791844072 9780791844083 0791844080

Abstract

The Radioactive Depth Analysis Tool (RADPAT) is a PhD bursary project currently being undertaken at Lancaster University in the UK. The RADPAT project involves the development of nuclear instrumentation capable of ascertaining depth of radioactive contamination within legacy plant materials such as concrete. This paper evaluates the merits of two types of detector; sodium iodide (NaI(Tl)) and cadmium zinc telluride (CZT), both of which have been identified as possible solutions for the final RADPAT detector. A bespoke concrete phantom has been developed to allow a set depth of simulated contamination to be obtained with a low measurement error within a concrete analogue: silica sand. Utilising this phantom, in combination with the selected detectors, a set of measurements have been obtained varied with increasing depth of caesium-137 contamination. By comparing the relative attenuation of the x-ray and -ray photo-peaks from the data-set to that suggested by a differential attenuation law, a set of model parameters can be obtained. This model, once calibrated, describes the contact depth of contamination with the relative intensity of the peaks in a measured spectrum with a high degree of accuracy. Thus, this technique allows for a set of measurements across the surface of a given material to obtain the inherent distribution of the depth of caesium-137 contamination. This paper is primarily interested in the ability of each detector type to derive the attenuation model, paying particular attention to the associated statistical uncertainty of the fitted parameters and thus the error in the derived depth. The paper describes the contributing effects of the inherent properties of each detector; effects such as their energy resolution, absolute efficiency as well as peak-to-Compton ratio. Finally a commentary on the applicability of each selected detector type is presented, including a comment on the extension the technique to a more generic, real world solution.