الفهرس 
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Abstract
The penetration of MeV positrons through amorphous and crystalline materials has been studied theoretically and experimentally and the base of development MeV positrons into a new probe in solid state physics and material science was established.
The first part of this work involves the theoretical studies. In both amorphous material, and crystal in random directions, penetration phenomena were described theoretically by multiple scattering theories. The differential multiple scattering cross section for high energy electrons and positrons has been evaluated using Goudsmit¬Saunderson theory and the Thomas Fermi potential. A Monte Carlo code using a condensed technique has been developed and used with the multiple scattering cross sections to evaluate the angular distributions of electrons and positrons for any desired target thickness. On the other hand the penetration of MeV positron beam aligned with an axis in crystal (axial channeling) was studied theoretically based on both classical and quantum mechanics descriptions.
In the second part, an experiment is presented to measure the multiple scattering of MeV positrons through thin polycrystalline films in both random and channeling direction. To perform the measurements, the first quantitative use of image plate technology was developed including calibration for energetic positron beams and data analysis. Channeling experiments also were performed on polycrystal and high quality crystal gold. For polycrystal gold, transmission measurements manifested the channeling effect on the angular distributions of MeV positrons. For high quality crystal, the channeling effect was revealed by direct observation of the wide-angle scattering channeling dip.
On the way of performing those experiments, new beam optics for extracting the slow positrons from a moderator mounted in a pelletron electrostatic accelerator is presented. The proposed system has been replaced the original design at the 3 MeV pelletron at the Lawrence Livermore National laboratory (LLNL) at US. A positron beam transport system has been also constructed to provide adjustable size and angular divergence beams to a target station. By that the (LLNL) positron facility was upgraded to
be the first monoenergetic MeV positron source for channeling and scattering experiments.
The final part of the work describes the design and construction of an experiment to combine MeV positron channeling with two quantum annihilation in flight for the purpose of probing electron densities in crystals. The first observation of two quantum annihilation in flight channeling is presented indicating the feasibility of using fast positrons as a local probe for electron distributions in crystals.