Yohannes, Teketel (Professor)Megerssa, Negussie (PhD)Tesfay, Hagos2021-01-132023-11-092021-01-132023-11-092015-06-06http://etd.aau.edu.et/handle/12345678/24644Dye/polymer based dosimeters are developed by various researchers for medical, industrial and environmental applications. Most of these radiochromic dosimeters are focused on applications related to detection of high dose ionizing radiation. Development of dosimeters from different materials such as polymers, dyes, semiconductors, metal oxides and other materials is an active research area. The development of a radiochromic dosimeter from cheap materials such as polymers and dyes for low dose radiation dosimetry is also getting much attention. At present different research groups are working on developing radiochromic dosimeters using dyes and polymers. Some polymethine cyanine dyes were studied for their dosimetric characteristics. The results of the studies show that these dyes could be promising materials for developing radiation dosimeters for the measurement of low dose radiation in medicine and environment. A traditional turmeric dye called curcumin was also studied in film form for high dose dosimetry. However, heptamethine dyes and curcumin have not been profoundly investigated for low dose dosimetry. Page iii On the other hand, conjugated polymers and other conventional polymers are being investigated for developing polymer based radiochromic dosimeters. Some promising results were reported especially for low dose radiotherapy and high dose industrial applications. In this research work, dosimetric studies were carried out on the heptamethine cyanine dyes, curcumin dye and P3HT solutions and polyvinyl alcohol (PVA) films using UV-Vis spectrophotometry, spectrofluorometry, mass spectrometry (MS), optical densitometry and Fourier transform infra-red spectroscopy (FT-IR) methods. The two heptemethine cyanine dyes and curcumin showed promising dosimetric characteristics for low dose applications. P3HT in chloroform with the addition of DDT also showed promising results opening for a possibility of developing a low dose dosimeter using P3HT solutions in other non-toxic solvents in the presence of less hazardous chemicals such as chloral hydrate and trichloroacetic acid as radiosensitizers instead of DDT. The heptamethine/PVA/HCl film nanocomposite doped with TiO2 nanoparticles showed enhanced dosimetric response confirming the catalytic role TiO2 nanoparticles play in improving the dosimetric characteristics of these dyes in solid state for low dose applications. A mechanism for the radiation-induced decomposition of the heptamethine dye solutions in chloroform was proposed based on the MS, FTIR and UV-Vis spectroscopic data. The proposed mechanism involves a two step reaction. In the first step, radiolysis of chloroform occurs, which results in radicals and stable molecules. In the second step, decomposition of the heptamethine dye occurs via interaction of the dyes with these radicals (Cl. and .CHCl2) and stable molecule (HCl) to produce smaller chromophoric groups. In the proposed mechanism, the various Page iv chromophoric groups formed are described based on UV-Vis, MS and FTIR data showing extensive loss of conjugation due to breakdown of the -bond of the polymethine bridge on interaction with radiolysis products of chloroform. The heptamethine dosimetric dye solutions also show visual color changes with intensity of color being proportional to absorbed doses which is very useful for precise monitoring of doses delivered to patients in radiotherapy applications. The shelf life of the pre-irradiated dye solutions also show good stability up to 20 days. The dosimetric dye solutions (heptamethine dyes and curcumin) prepared from non-toxic solvents such as ethanol and acetone in the presence of radical generating species trichloroacetic acid and chloral hydrate showed promising results which will have great potential for real low dose applications in medicine and environment.enHeptamethine DyesCurcuminX-Ray RadiationGamma RadiationGrayRadiation DoseDosimetryPolyvinyl AlcoholRadiochromicEnvironmentalMedicalThesis