Radiation-Induced Polymerization of Polymethacrylic Gel for Dosimetry
Mustafa, Iskandar Shahrim (2006) Radiation-Induced Polymerization of Polymethacrylic Gel for Dosimetry. Masters thesis, Universiti Putra Malaysia.
The aim of the present work is to investigate the effect of radiation on methacrylic acid (MAA) crosslinked with N, N’-methylene-bisacrylamide (BIS) for the purpose of developing a polymer gel dosimeter, namely, polymethacrylic gel (PMAAG). PMAAG of different concentrations of MAA and BIS were irradiated with the absorbed doses ranging from 0 Gy to 19 Gy. Using Raman spectrophotometer, five peak intensities were identified and represents the assigned bonding for C=C (2238 cm-1) of MAA, C=C (1634 cm-1) of BIS, C-C (2110 cm-1) of PMAA, C=O (1795 cm-1) of PMAA, CH2 (2905 cm-1) of PMAA, which have strong modes of vibration in the band positions. The Raman peak intensity y as a function of absorbed dose D was found to have a monoexponential expression in the form; −+=−010DDeAyy. The dose sensitivity D0 and half dose D1/2 were obtained and found to increase with the concentrations of MAA monomer and BIS crosslinker. The dose correlation factor of BIS, kBIS is always higher than kMAA of MAA (kBIS > kMAA) for all C-C, C=C, C=O and CH2 stretching modes, indicating BIS is a very significant parameter in the polymerization process. Additionally, a Nuclear magnetic resonance (NMR) spectrometer was used in order to measure the relaxation time of polymethacrylic (PMAA) gel dosimeters. The relaxation rate (ΔR2) dose sensitivity value (12.5 + 0.1 Gy) of MAA monomer by Lepage, et al 2001 is comparable with PMAAG experimental value gained which are 12.6 + 0.1 Gy. A comparison between and indirect measurements of polymer formed along with consumptions of monomer and crosslinker are also obtained from this experimental work. Finally, a UV-Vis spectrophotometer was used to records PMAAG degree of absorption in order to determine the accuracy of PMAAG. The PMAAG has a mean value of absorption of 0.614 at 375 nm. The dose derived from PMAAG is comparable to Fricke dosimeter and ionization chamber readings between 4.7 ± 0.1% and 11.6 ± 0.1%. The dose errors of less than 10 ± 0.1% are considered acceptable in radiation processing, an improvement of accuracy less than 5.0 ± 0.1% is acceptable in radiotherapy.
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