Investigation of chelating agents/ligands for Fricke gel dosimeters

The Fricke solution is an absolute dosimeter which can be combined with some metal-binding organic ligands and thus show measured radiation doses through visible light absorption effects. Adding the solution to a gel matrix also allows mapping doses three-dimensionally, and is known as Fricke-gel dosimetry. The latter has some drawbacks that hinder its practical usage for 3D mapping, namely signal diffusion effects and spontaneous color changes due to auto-oxidation. Ligands play a major role in this respect and xylenol orange has been used extensively. Several alternative ligands and their interactions with Fricke solutions and gels were investigated in this study. Among these ligands, calcichrome (CH), eriochrome blue (EB), methylthymol blue (MTB), and naphthol green (NG) showed the required differentiation between optical absorbance of ferrous vs ferric ions. While our study confirmed the overall advantages of using xylenol orange, it also suggests that methylthymol blue offers potential worthy of further investigation.