Raman Spectroscopy of Irradiated Normoxic Polymethacrylic Acid Gel Dosimeter

A quantitative analysis of the decreasing rate of the monomer and increasing rate of the polymerization was made by monitoring radiation level increments using Raman spectroscopy within the therapeutic radiation range for a normoxic polymethacrylic acid gel dosimeter. The gel dosimeter was synthesized by stirring materials such as gelatin, distilled water, methacrylic acid, hydroquinone and tetrakis phosphonium chloride at 50 .deg. C, and the synthesized gel was contained in a 10- mm diameter and 32-mm high vial to conduct measurement. 24 hours after gel synthesis, it was irradiated from 0 Gy to 20 Gy by 2 Gy using a Co-60 radiotherapy unit. With use of the Cryo FE-SEM, structural changes in the 0 Gy and 10 Gy gel dosimeters were investigated. The Raman spectra were acquired using 532-nm laser as the excitation source. In accordance with fitting the changes in C-COOH stretching (801 cm^-1), C=C stretching (1639 cm^-1) and vinyl CH₂ stretching (3114 cm^-1) vibrational modes for monomer and CH₂ bending vibrational mode (1451 cm^-1) for polymer, sensitive parameter S for each mode was calculated. The values of S for monomer bands and polymer band were ranged in 6.0 ± 2.6 Gy and 7.2 ± 2.3 Gy, respectively, which shows a relatively good conformity of the decreasing rate of monomer and the increasing rate of polymerization within the range of error