الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Thermoluminescence (TL) is one member of a large family of luminescence, in which TL is a temperature stimulated light emission from a crystal after removal of excitation. Many natural or synthetic crystals exhibit thermoluminescence properties. Fluorite (natural CaF2) is amongst the earliest known TL emitting materials and was one of the first to be used as one of sensitive radiation dosimetry. The characteristics of natural calcium fluoride depends upon its origin and its chemical composition, where a wide variety of different impurities acting as activators.
In this thesis The TL-properties were studied for different samples of locally natural fluorite (N-CaF2) and synthetic calcium fluoride (CaF2:Dopant) using Gamma dose Co-60 source. The usability of these samples in assessment of radiation fields are evaluated for age determination of natural samples. The contents of the present thesis have been divided into five chapters; introduction, theoretical aspect, apparatus & materials & procedures, results & discussion and conclusions.
The first chapter: is dedicated for a general introduction and gives a brief summary about luminescence and thermoluminescence phenomenon as a type of the luminescence. The TL-materials, natural fluorite, factor affecting TL and the TL application are listed. Also, unit of radiation field& safety are listed with the natural radiation sources of exposure. Historical review of some previous works has been mentioned. And finally the work plan among this study is mentioned at the end of this chapter.
The second chapter: exhibits theoretical background to the TL-mechanism in view of band theory of solids; traps and recombination centers. Simple model which is based on the energy band model followed by general theories of the glow curve (by first, second, general and mixed-order kinetic) are listed for thermoluminescence analysis. Methods of analysis by partial curve analysis and peak position method have been mentioned. The external and internal dose rate determination for TL dating application is discussed. In which, evaluation of the absorbed dose by additive dose, regeneration dose, phototransfer TL and plateau test methods also are listed.
The third chapter: discusses the apparatus, materials, methods of experiments, and irradiation sources used. Six different samples of locally natural fluorite with different colors were specially selected for experiments. The natural samples were collected from Gattar mountain area which located in eastern desert-Egypt (27°00’-27°10’N 33°20’-33°30’E). It also gives a view of natural samples preparation including samples collection, cleaning, washing, crashing, sieving, and annealing. Synthesis of samples (CaF2:Dopant) starting from finding and providing the samples needed, chemical preparation, dopant type (Gd, Dy, Sm and Mn), dopant concentration, chemical treatment, heat treatment, washing, drying, crashing, sieving, and annealing have been discussed.
The fourth chapter: compromises the results and discussion besides physical explanation of the obtained data. The natural fluorite samples (F1-F6) show more or less the same glow curves behavior with eight glow peaks (P1-P8) obtained by Tm(Ea)- TStop method under the four observed peaks (P I- P IV), three peaks under the first maximum PI and also three peaks under the dosemitric peak ( peak No. P III). The peaks position, intensity and sharpness changed from sample to another, which can be referred to the variation in dopant concentrations that obtained by different methods of analysis. The temperature of the maxima intensities seems to be around 120 oC for P I (P1,95; P2,102; P3,122oC), 197 oC for P II (P4), 300 oC for P III (P5,267; P6,307; P7,332oC) and 405oC for P IV (P8) respectively. Corresponding to respective activation energy of the trap depth of about 1.1, 1.17, 1.24, 1.52, 1.78, 1.93, 2.02 and 2.3 eV and life time(τ) of about1.8x10-4 , 3.73x10-4 ,4.92x10-3 ,1x102 , 1.34x106 , 3.29x108 ,1.04x1010 and 3.59x1014 yr for P1-P8 respectively at 10oC/s heating rate (β). The peaks positions (Tm) are shifted to higher value with increasing β (varies from 1oC/s to 25oC/s). The peak height and the area of P I and P II have no appreciable change with increasing heating rate, P III height and area decrease from 1-7 oC/s then increase linearly with increasing heating rate (7-25oC/s). In the other hand P IV height and area decrease with increase the heating rate.
The annealing conditions (temperature & time) show that the optimum annealing condition is 450oC for 30 minute, for sample grain size range from 40-200 µm that almost having the maximum TL response. The dose response curve of γ-irradiated natural CaF2 (F1- F6) is linear (up to 30 Gy), supralinear (from 30Gy - 1kGy) after which saturating occurs. Also, the fluorite shows photo-transfer (from deep traps) sensitivity by UV exposures which increased almost linearly with the UV exposure light after which the PTTL glow peak heights show saturation. The PTTL intensities are increased by increasing the pre-gamma irradiation and the saturation region comes early with increasing the historical gamma dose.
The fading effect at room temperature (RT) on glow curve of natural CaF2 shows different behavior with the maximum observed (P I, P II, P III and P IV) than that of the individual peaks. In P I and P III the Tm is shifted to a higher value by increasing the time of storage, while the shift is negligible in P II and P IV. The shift situations in the observed peaks are different from the real situation in the individual one.
The synthetics CaF2:Dopant (Mn, Gd, Sm, Dy, Gd&Sm, Gd&Dy and Gd&Dy&Sm) are prepared by chemical reaction. The characteristic glow curves, kinetic parameters (E, s, P and τ), dose response and fading effect were varied with dopant types and concentration, and differ than that of natural CaF2.
The concentration of the radionuclide in F6 sample is found to be equal to 9.2±0.53 Bq/Kg for U-235, 208.86±14 Bq/Kg for U-238, 23.3±1.4 Bq/Kg for Th-232 and 268.9±3.4 Bq/Kg for K-40. Which gives self dose rate about 51.365, 3.302 and 2.375mGy/a from Alpha, Beta and Gamma-ray exposure respectively. The annual dose rate is found to be about 10.19027 mGy/a. The age of deposition of fluorite (F6) is estimated by palaeodose and dose rate evaluations. The palaeodose is determined by different methods; the plateau test level, the additive dose method (AD), the regeneration method and PTTL method. An average age of deposition over PTTL and AD methods of about 57.566Ka is estimated, which represent the last firing or heating time.
The fifth chapter: includes the conclusions about the obtained results.