Measurements of the Fe super(3+) diffusion coefficient in Fricke Xylenol gel using optical density measurements

• Published in: Applied radiation and isotopes Vol. 90; pp. 241 - 244
• Main Authors: Oliveira, Lucas Nonato de, Sampaio, Francisco Glaildo Almeida, Moreira, Marcos Vasques, Almeida, Adelaide de
• Format: Journal Article
• Language: English
• Published: 01-08-2014
• ISSN: 0969-8043
• DOI: 10.1016/j.apradiso.2014.04.004

In Fricke dosimetry, optical density measurements are performed some time after dosimeter irradiation. Values of the diffusion coefficient of Fe super(3+) in Fricke Xylenol gel (FXG) are necessary for determining the spatial distribution of the absorbed dose from measurements of the optical density. Five sets of FXG dosimeters, kept at different constant temperatures, were exposed to collimated 6 MV photons. The optical density profile, proportional to the Fe super(3+) concentration, at the boundary between irradiated and non-irradiated parts of each dosimeter was measured periodically over a period of 60 h. By comparing the experimental data with a function that accounts for the unobserved initial concentration profile of Fe super(3+) in the FXG, we obtained diffusion coefficients 0.30 plus or minus 0.05, 0.40 plus or minus 0.05, 0.50 plus or minus 0.05, 0.60 plus or minus 0.05 and 0.80 plus or minus 0.05 mm super(2)/h for the temperatures 283.0 plus or minus 0.5, 286.0 plus or minus 0.5, 289.0 plus or minus 0.5, 292.0 plus or minus 0.5, and 296.0 plus or minus 0.5 K, respectively. The activation energy of Fe super(3+) diffusion in the gel, 0.54 plus or minus 0.06 eV, was determined from the temperature dependence of the diffusion coefficients.