Evaluation of ferrous Methylthymol blue gelatin gel dosimeters using nuclear magnetic resonance and optical techniques

Abstract

Signal development of irradiated Methylthymol blue (MTB) Fricke gelatin gel dosimeter was studied using nuclear magnetic resonance (NMR) in terms of the spin-spin relaxation rate (R2) of hydrogen protons within the water molecule. The optical properties of MTB gel were also studied using a spectrophotometric technique. The gel dosimeter presents a linear response for doses up to 20 Gy with ultraviolet visible (UV-Vis) spectrophotometry and 40 Gy with NMR. For a 0.1 mM MTB concentration and dose of up to 10 Gy, the sensitivity of the gel response analyzed by a spectrophotometer is 0.077 a.u. Gy−1 at 620 nm with a linear coefficient of (r2 = 0.998), while the R2 sensitivity is 0.02 s−1 Gy−1 with a linear coefficient of (r2 = 0.998). The sensitivity of the Fricke-MTB dosimeter was higher when compared with the Fricke-XO dosimeter. The dose rate and photon energy beams were dependent of the absorbance and R2 dose sensitivity, as observed over the range studied. The Fricke-MTB gelatin dosimeters can be scanned at higher wave lengths than the conventional Fricke-XO gelatin formulations.