الفهرس 
Definition of the phenomena of ThermoluminescenceOnly 14 pages are availabe for public view
 |  | from | 174 |  |  |
| | | from | 174 | | |
Abstract
This thesis is a study of some dosimetric properties of Lithium Florid (LiF), manufactured by Sigma Aldrich Chemical Company with purity of 99.99%, in the form of powder, a pristine (as received) LiF was milled for 1 hour and compressed in form of chips then annealed for 1 h at 600 oC to get rid of low temperature dislocations. In this study, the Thermoluminescence (TL) readings were measured at least for seven to nine samples for the purpose of reliable statistics. The aim of this thesis is used ball milling method as an alternative to dopants (impurities) to induce structure defects (e.g. dislocation) that will play the major role in TL process instead to dopants, because pure LiF has very limited use in radiation dosimetry since the density and types of the internal traps are limited. For that reason, LiF usually are doped with different elements such as Mg and Ti in (TLD-100) to enhance its TL properties and to be suitable for dosimetry applications.
This thesis includes five chapters in addition to conclusion, as follows:
Chapter I: INTRODUCTION.
In this chapter, a brief introduction on the phenomenon of the Thermoluminescence has been introduced showing how the TL process takes place in general. Different kinetic models have been discussed where such models interpret the possible different mechanism of charge carriers with opposite signs and how the recombination process takes place that result in TL signal. Different types of defects in regular crystal structure have been discussed. The main essential properties of the TL material have been discussed; the availability of the most known TL materials have been discussed as well as their different applications in different fields
Chapter II: LITERATURE REVIEW
In this chapter, a review on the properties of LiF as a most widely known TLD material has been introduced. TL properties of the pure or natural LiF has been also shown. LiF with different dopants will be presented showing how such impurities can significantly enhance the sensitivity of the LiF compared to pure or natural LiF.
Chapter III: THEORETICAL ASPECTS
In this chapter, the theoretical bases of exploration of the glow peaks parameters with different methods have been introduced. Special interest has been given to the Glow Curve DeConvlution GCDC approach. GCDC approach has been used in this thesis to explore the different energy trap parameters of the glow curve. Also, we have shown how the ball milling can be used to decrease the crystal size to nano scale and then it have shown that ball milling can introduce crystal defects in LiF (namely dislocations). Such type of defects could be used as an alternative of impurities to enhance the TL sensitivity of the LiF material. Basics of synchrotron radiation have been briefly discussed where such radiation is used to perform high quality powder X-ray diffraction PXRD. Finally, brief description of Whole Powder Pattern Modeling (WPPM) have been introduced; such model is used to carry out line profile analysis (LPA) to explore the microstructure properties of the ball milled LiF that will be used to find the dislocation density of the LiF.
Chapter IV: MATERIAL AND METHODS
In this chapter, we have shown in details how the LiF samples were prepared and what instruments and techniques were used for such purpose. A brief description of the MCX beamline at the Italian synchrotron ELETTRA in Trietse has been introduced. The X-ray diffraction setup at MCX beamline has been presented. Finally, the complete system for reading TL signals has been shown in details along with the main parameters that control the output TL signal.
Chapter V: RESULTS & DISCUSSION
In this chapter, the results of the PXRD (of the pristine and ball milled LiF samples) that have been performed at MCX beam line were presented. LPA was carried out by means of WPPA model and the dislocation densities in both samples were evaluated. The different TL properties of the prepared LiF chips were then investigated; this includes the effect of: 1) heating rate at constant gamma dose, 2) different gamma ray doses, 3) fading on the output TL integral intensity. It has been found that the glow curve of the prepared LiF chip has 7 glow convoluted peaks and three of them are considered to be dosimetric peaks. All glow peaks have been deconvoluted by means of the CGCD approach and there relevant parameters were identified. However, detailed GCDC has been carried out on the glow curves of fading experiment. This because it has been noticed that there is a significant decrease in maximum peak intensities of some peaks and other peaks show a significant increase in other peaks. This behavior implies internal retrapping of charge carriers during storage of the prepared LiF chips for long time. All results were discussed in details.
CONCLUSION
Here we present the main conclusions resulted from the current study that could be summarized as follow: (1) LPA by means of WPPA is very essential as advanced technique to evaluate the microstructure details of the nanocrystalline materials; (2) effective high quality LPA could be achieved when high quality X-ray source (e.g. synchrotron radiation) is used for powder diffraction measurements; (3) for the first time we proved that the ball milling technique could be used to introduce internal structural defects that can play important role in enhancing TL intensity; this technique could be considered as an effective alternative of impurities that usually added to LiF. (4) The prepared LiF chips by means of techniques presented in this study can be used as a promising high gamma dosimeter.