Abstract
The effects of ionizing radiation in different compositions of polymer geldosimeters are investigated using FT-Raman spectroscopy and NMR T2relaxation times. The dosimeters are manufactured from differentconcentrations of comonomers (acrylamide andN,N'-methylene-bis-acrylamide) dispersed in different concentrations ofan aqueous gelatin matrix. Results are analysed using a model of fastexchange of magnetization between three proton pools. The fraction ofprotons in each pool is determined using the known chemical composition ofthe dosimeter and FT-Raman spectroscopy. Based on these results, thephysical and chemical processes in interplay in the dosimeters are examinedin view of their effect on the changes in T2. The precipitation ofgrowing macroradicals and the scavenging of free radicals by gelatin areused to explain the rate of polymerization. The model describes the changesin T2 as a function of the absorbed dose up to 50 Gy for the differentcompositions. This is expected to aid the theoretical design of new, moreefficient dosimeters, since it was demonstrated that the optimum dosimeter(i.e, with the lowest dose resolution) must have a range of relaxationtimes which match the range of T2 values which can be determined withthe lowest uncertainty using an MRI scanner.
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