Characterization of monomer/crosslinker consumption and polymer formation observed in FT-Raman spectra of irradiated polyacrylamide gels

Abstract

Fourier transform Raman spectroscopy was undertaken in the study of irradiated polyacrylamide gels (PAGs) used in 3D radiation dosimetry. By employing correlation techniques, monomer and crosslinker consumption were characterized in the spectra as a function of absorbed dose. The consumption of both monomer and crosslinker is monoexponential up to 13 Gy, although the rates of consumption differ for the two molecules. A sensitivity parameter, D0, in the exponential function has been used to characterize this difference. Up to 13 Gy, D0(acr) = 12 +/- 2 Gy while D0(bis) = 8.0 +/- 0.5 Gy, indicating that bis is consumed at a greater rate than acrylamide and that bis is the limiting factor in the onset of gel saturation, for a gel composition of 6% by weight total monomer (6%T) and where 3% of the total monomer is crosslinker (50%C). Direct evidence of polymer formation was observed in the Raman spectra of irradiated PAG. Polymer formation is monoexponential to a dose of 13 Gy, with a sensitivity parameter of D0(poly) = 14 +/- 2 Gy. This is in good agreement with the consumption rate of acrylamide. The exponential nature of the polymer formation observed here is compared with existing MRI and x-ray CT dose response measurements previously reported to be linear. The results confirm previous studies indicating that Raman spectroscopy provides a direct and useful tool for characterization of irradiated PAG.