Measurements of the Fe³⁺ diffusion coefficient in Fricke xylenol gel using optical density measurements.
In Fricke dosimetry, optical density measurements are performed some time after dosimeter irradiation. Values of the diffusion coefficient of Fe(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(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(3+) in the FXG, we obtained diffusion coefficients 0.30±0.05, 0.40±0.05, 0.50±0.05, 0.60±0.05 and 0.80±0.05 mm(2)/h for the temperatures 283.0±0.5, 286.0±0.5, 289.0±0.5, 292.0±0.5, and 296.0±0.5 K, respectively. The activation energy of Fe(3+) diffusion in the gel, 0.54±0.06 eV, was determined from the temperature dependence of the diffusion coefficients.
Instituto Federal de Educação, Ciência e Tecnologia de Goiás-IFG, 75400-000 Inhumas, GO, Brazil. Electronic address: lucas.oliveira@ifg.edu.br.
Lucas Nonato
LN
de Oliveira
Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto-FFCLRP - Universidade de São Paulo - USP, 14040-901 Ribeirão Preto, SP, Brazil.
Francisco Glaildo Almeida
FG
Sampaio
Instituto de Radioterapia e Megavoltagem de Ribeirão Preto-IRMEV, 14010-180 Ribeirão Preto, SP, Brazil.
Marcos Vasques
MV
Moreira
Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto-FFCLRP - Universidade de São Paulo - USP, 14040-901 Ribeirão Preto, SP, Brazil.
Adelaide
A
de Almeida
Diffusion coefficient; Fricke Xylenol gel; Optical density