الفهرس 
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Abstract
The aim of the present work is to study the neutron transmission through bulk imperfect single crystals having different structure types along with the feasibility of using MgF2 single-crystal as an efficient thermal neutron monochromator and/or filter is given. Moreover, a simulation study for the production of 2KeV quazi-mon-energetic neurton beam at the exit channel port of both nuclear reactor and neutron accelerator is also investigated.
A formula is given that permits the calculation of the neutron transmission through bulk imperfect single crystals as a function of wavelength at both room and liquid nitrogen temperatures. The formula takes into consideration the crystal structure type and the orientation of its cutting plane w. r. t. the incident neutron beam direction. The reflecting power of the Bragg reflections from the allowed hkl planes are calculated taking into account the primary and secondary extensions inside the bulk crystal. The crystal is considered to consist of thin layers such that the extensions inside the layer are negligible.
A computer code BISCF written in FORTRAN-77, developed in the neutron physics laboratory, Nuclear Research Center, Atomic Energy Authority, Egypt, has been used to carry out the required calculations of the neutron transmission through bulk imperfect orthorhombic and hexagonal closed packing (HCP) crystal structure types.
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It was found that the calculated shape and area of the dips, due to Bragg reflections in the neutron transmission through 10mm Cu single crystal cut along its (111) and (002) planes at various take-off-angles, are in agreement with the experimental data for layer thickness varying between (10-60)µm. A good agreement was also obtained between the calculated Bragg reflections from 22mm Zn single-crystal cut along its (002) plane and experimental ones for the same layer thickness as the latter. While for 100mm MgO, it is from 10-500 µm at R.T. and 10-550µm at liquid nitrogen temperature. Such overall agreement justifies the applicability of the used formula and the designed computer code.
The calculation of both neutron reflectivity and attenuation of single–crystal magnesium fluoride (MgF2) as a function of wavelength at both room temperature and 77 K is carried out using a simple formula. A computer program MgF2 written in FORTRAN-77, has been developed to carry out the required calculations for the single- crystal MgF2, when it used as a neutron monochromator and/or filter.
The monochromatic characteristics of single-crystal MgF2 is detailed in terms of the optimum crystal cutting plane, mosaic spread, thickness and reactor moderating temperature for efficient neutron reflectivity within the wavelength band from 0.1nm up to 0.45nm. Calculation shows that, 7mm thick of MgF2 single-crystal cut along (111) plane having 0.50 FWHM on mosaic spread are the optimum parameters when, it used as a monochromator at neutron wavelengths shorter than 0.2nm. However, the integrated neutron intensity of 2nd and 3rd orders from a thermal reactor flux is even higher than that of the 1st order one at neutron wavelengths longer than 0.2 nm. While, from a cold reactor flux, the use of the single- crystal MgF2 (110) as a neutron monochromator free from higher order contaminations at λ≥ 0.38 nm are more appreciated.
A feasibility study of using single-crystal MgF2 as a neutron filter is also detailed in terms of the optimum crystal orientation, mosaic spread, thickness and temperature for efficient transmission of thermal-reactor neutrons. Calculation shows that 100mm thick MgF2-single crystal cut along (110) plane cooled to liquid nitrogen temperature, with 0.05o FWHM on mosaic spread, is a good thermal neutron filter, with high effect-to-noise ratio.
A simulation study for the production of 2KeV filters of quasi-mono-energetic neutrons based on the deep interference minima in the Sc-45 total cross-section was carried out. A computer code QMENF-II was adapted to calculate the optimum amounts of the Sc-45 as a main filter element and additional component ones to obtain sufficient intensity at high resolution and purity of the filtered quasi-mono-energetic neutrons. The emitted neutron spectrum from nuclear reactor and from the reaction of 2.6 MeV protons on a lithium fluoride target at the accelerator beam port, are used for simulation.
The new method used , in the present thesis, to select the optimum 45Sc thickness as a main filter element and additional component ones as the maximum of the rate of change in purity is proved to be useful and economic for filtering composition. Based on Sc-45 and Zn-64 as an additional element the obtained quasi-mono-energetic beams were found free from the disturbing dips.
The high flux density and purity of the suggested filters at the accelerator beam port are appreciated for the use for BNCT.