Characterization of the chemical stability of irradiated N-isopropylacrylamide gel dosimeter

• NMR and FT-Raman spectroscopy are used to characterize the monomer and cross-linking agent of NIPAM gel.
• The NIPAM gel dosimeter exhibited good linearity, high sensitivity, and no energy dependence.
• Chemical stability of irradiated NIPAM gel dosimeter can be predicted by dose–intensity curve.

An investigation of the normoxic NIPAM gel dosimeter has been undertaken. The NIPAM gel dosimeter used in the current study was mainly composed of gelatin, NIPAM, N,N′-methylenebisacrylamide (BIS), and distilled water. This study aims to measure the change in the chemical structure of the NIPAM gel dosimeter after irradiation via the 13C-NMR, 1H-NMR, and Fourier transform Raman (FT-Raman) spectra. The 13C-NMR experimental results show that the C=C bonds of NIPAM and BIS are at 126.74 and 131.62 ppm, respectively. The intensity of the C-C bond of the NIPAM gel dosimeter increases with the absorbed dose, and the dose–intensity curve of the C–C bond is determined by y=0.0506+79.9(1−e0.16x)y=0.0506+79.9(1−e0.16x) (R2=0.9997). 1H-NMR and FT-Raman can also effectively determine the positions of the C=C bonds of NIPAM and BIS, and the intensity decreases as the absorbed radiation dose increases. Hence, 13C-NMR, 1H-NMR, and FT-Raman spectrometers can effectively detect the changes in the chemical structure of the polymer gel dosimeter after irradiation and successfully determine the D50 dosage in the NIPAM gel dosimeter.