Abstract
Hydrophilic materials which refer to a group of cross-linked polymers originally developed in the 60s to produce soft contact lenses are characterised by an equilibrium water uptake in the range 15-95 % by wet weight when hydrated in water or normal saline solution at 25 degrees C. This ability to absorb controlled amounts of water makes them suitable human tissue substitutes. Four types of hydrophilic materials of different composition and thickness were placed between a Na-22 calibrated point source and a single LaBr3: Ce (5 %) detector (Saint-Gobain) at a fixed distance between source and detector. The scatter-to-peak ratio was determined by selecting five scatter angle windows between 25 and 50 degrees (467-376 keV), at 5 degrees intervals, to study how the ratio varied with attenuating material, thickness and composition. From photon spectra recorded a 'best' estimate of the depth of the source in the hydrophilic material was obtained by finding the most sensitive scattering window. Theoretical and practical models of the source-to-detector geometries are included and discussed.