12th International Conference & Workshop Medical Physics in the Baltic States, 2015 RAMAN SPECTROSCOPY OF POLYMERIZATION PROCESSES IN npag AND nmag DOSE GELS Neringa VAIČIŪNAITĖ 1, Rimas ŠEPERYS 2 1 Physics Department, Kaunas University of Technology 2 SME Šeši partneriai 1
INTRODUCTION Polymer gels have been proven to be a valuable tool for determination of beam dose characteristics and 3D radiation dose measurements for medical purposes [1-3]. A typical gel dosemeter consists of water, gelatin agent, monomers and a cross-linker comonomer [4,5]. Many chemical compositions have been proposed for dosimetric purposes, but only a few have been carefully tested [4,5]. To evaluate the interaction between monomer consumption and polymer production is very important [6]. 2
AIM OF THE STUDY The aim of this study was to identify the radiation interaction mechanisms on photon irradiated npag and nmag polymer gels in accordance with analysis of characteristic vibrational modes of dose gel components
POLYMER GELS PREPARATION AND IRRADIATION npag nmag 89% Highly purified water 86% Highly purified water 5% Gelatine 8% Gelatine 3% Acrylaimde 6% Methacrylic acid 3% N; N- methylenebisacrylamide 10 mmol/l Hydroxymethyl phosphonium chloride - 10 mmol/l Hydroxymethyl phosphonium chloride Fig.1. Preparation of the dose gel. npag and nmag polymer gels were irradiated by Co 60 photon source of teletherapy unit (ROKUS M) by 2 Gy dose. Dose rate of 0.03 Gy/ min, SSD 100 cm, field opening 10 10 cm. 4
POLYMER GELS PREPARATION AND IRRADIATION Fig. 2. Micro Raman invia Renishaw c) d) Fig. 3. Non irradiated npag gel, Non irradiated nmag gel, c) npag irradiated by 2 Gy Co-60, d) nmag irradiated by 2 Gy Co-60. Micro Raman (invia Renishaw) vibrational spectroscopy of the irradiated copolymerized npag and nmag samples in cuvettes was performed on the 7th post-irradiation day.
RESULTS AND DISCUSSION npag Fig.4. Chemical structure of acrylamide, polyacrylamide. Fig.5. Micro -Raman spectra of npag polymer dose gel: non irradiated, irradiated by 2 Gy by Co 60 photon source. 6
2880 2936 2880 2936 1256 1285 1256 1285 npag RESULTS AND DISCUSSION FWHM = 310,9 FWHM = 1229,1 c) d) Fig.6. Polymer development observed in Raman spectra of normoxic polyacrylamide (npag) gel in the range of 900-1400 cm -1 and 2800-3200 cm -1., c) Non irradiated npag gel;, d) irradiated npag gel. FWHM = 121,7 FWHM = 213,6
RESULTS AND DISCUSSION nmag Fig.7. Chemical structure of methacrylic acid, polymetchacrylic acid. Fig. 8. Raman spectra of nmag polymer dose gel: non irradiated, irradiated by 2 Gy by Co60 photon source. 8
2955 3114 2955 3114 539 539 nmag RESULTS AND DISCUSSION FWHM = 111,4 c) FWHM = 1198,8 d) Fig. 9. Polymer development observed in Raman spectra of normoxic methacrylic acid (nmag) gel at the range of 450-600cm-1 and 2000-3200 cm-1., c) Non irradiated nmag gel;, d) irradiated nmag gel. FWHM = 102,8 FWHM = 290,7
CONCLUSIONS Photon irradiation of Co 60 was applied to normoxic npag and nmag polymer dose gels to perform a polymerization process. The Micro-Raman spectra and full-width half-maximum calculations, showed the incensement of polymer representing vibrational bands and sharp reduction of monomer fraction. The reduction of BIS proved the theory of cross-linker consumption and its importance in network structure formation. The results agreed with the studies of other researchers, however more tests are needed to evaluate the consumption rate of monomers and cross-linker. 10
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