Nuclear magnetic resonance analysis of a chemically cross-linked ferrous–methylthymol blue–polyvinyl alcohol radiochromic gel dosimeter

Abstract

A new formulation of hydrogel dosimeter consisting of ferrous–methylthymol blue (MTB)–polyvinyl alcohol (PVA) cross-linked chemically with glutaraldehyde (GTA) was studied and evaluated by nuclear magnetic resonance analysis by means of the R2 spin-spin relaxation rate. Previous optical studies of this transparent solid chemically cross-linked gel showed important dosimetric features in terms of sensitivity, auto-oxidation rate, and diffusion. This study shows that the MTB-PVA-GTA dosimeter has a reproducible linear dose response up to 40 Gy. For the optimum formulation of 0.1 mM MTB, 2.5% PVA, and 26.6 mM GTA, the measured R2 sensitivity was higher than that of traditional natural matrix–containing gels (MTB-gelatin) and all other reported PVA gel–based radiochromic dosimeters with MTB, xylenol orange (XO), or GTA (MTB-PVA, XO-PVA, XO-PVA-GTA). Additionally, the auto-oxidation rate was approximately ten times lower than that of the Fricke-MTB-gelatin system, which is consistent with the spectrophotometry results. The results of the independent experimental spectrophotometry and nuclear magnetic resonance analyses indicate that the transparent cross-linked dosimeter has good and consistent dosimetric features.