الفهرس 
Neutron Physics ReviewOnly 14 pages are availabe for public view
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Abstract
The aim of the present work is to study the neutron monochromatic and filtering features of both poly- and mono-crystals with different crystal structures. The present study is concerning the calculation of total thermal neutron cross-section and transmission through Poly- and mono-crystalline BeO and SiO2 and their use as a whole thermal neutron filter. Also the use of NaCl and PbF2 single-crystals as highly efficient neutron monochromators and/or filters is also given.
Moreover, a simulation study for the production of quasi-mono-energetic neutron beams at the exit channel port of both nuclear reactor and proton accelerator is investigated. A general formula is given that permits the calculation of the neutron cross-section, transmission and reflectivity of single crystal with a particular orientation as a function of wavelength at booth room and liquid nitrogen temperatures. The formula takes into consideration the crystal structure type and the orientation of its cutting plane with respect to 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 extinctions inside the bulk crystals. Where, the crystals are considered to consist of thin multi layers to neglect the extinction effects. Computer codes ”HEXA-FILTERS” and ”CUBIC-MONO” written in ”FORTRAN-77” were developed in the Neutron Physics Laboratory, Nuclear Research Center, Atomic Energy Authority, Egypt, to carry out the required calculations for hexagonal and face centered crystal structures.
It was found that that 25 cm thick of polycrystalline BeO cooled at liquid nitrogen temperature is a good filter for neutron wavelengths longer than 0.46 nm. While, 50 cm of SiO2, for neutrons with wavelengths longer than 0.85 nm is with much less transmission than the later. It was also found that 10 cm of BeO and 15 cm SiO2 thick mono-crystals cut along their (002) plane, with 0.5o FWHM on mosaic spread and cooled at liquid nitrogen, are a good thermal neutron filter, with high effect-to-noise ratio.
The monochromatic features of NaCl and PbF2 bulk single-crystals are discussed in terms of orientation, mosaic spread, and thickness within the wavelength band from 0.04 up to 0.7 nm. Calculations shows that a 7 mm thick of NaCl (FCC structure) single crystal cut along its (200) plane having 0.5o FWHM are the optimum parameters when it is used as a monochromator with high reflected neutron intensity from a thermal reactor flux. Furthermore, at wavelengths shorter than 0.18 nm it is free from the accompanying higher order ones.
While, PbF2 (FCC structure) with the same parameters as NaCl, and cut along its (111) plane has reflected neutron intensity more than the later. For a cold reactor flux, the first-order neutrons reflected from both NaCl and PbF2 are free from the higher orders up to 0.58 nm and 0.63 nm respectively. A formula is given that permits the calculation of the total cross-sections of NaCl and PbF2 single-crystals as a function of neutron energy at both R.T. and L.N. temperatures. It was found that 5 cm of PbF2 (111) and 5 cm of NaCl (100) having 0.50 FWHM on mosaic spread and cooled at L.N., are a good thermal neutron filters, with high effect-to-noise ratio.
Filtered neutron techniques were applied to produce quasi-mono-energetic neutron beams in the energy range of (1.5-133) keV at research reactors. A simulation study was performed to characterize the filter components and transmitted beam lines. The filtered beams were characterized in terms of the optimal thickness of the main and additive components. The filtered neutron beams had high purity and intensity, with low contamination from the accompanying thermal emission, fast neutrons and -rays.
A computer code ”QMNB” was developed in the ”MATLAB” programming language to perform the required calculations. The newly developed filter for neutrons with energies of 1.5 keV is favored for application in both nuclear measurements and BNCT because it has high resolution at high flux density and low contamination of generated γ-rays.
Moreover, the flux densities of the suggested filters are greater than those obtained by other authors at almost the same purity and resolution. At the accelerator port using the generated neutron spectrum from a Li (p, n) Be reaction filtered neutron techniques were applied to produce quasi-mono-energetic neutron beams in the energy range of (1.5-7.5) keV. A simulation study was performed to characterize the filter components and transmitted beam lines. The feature of the filtered beams is detailed in terms of optimal thickness of the primary and additive components.
A computer code ”QMNB-AS” is developed to carry out the required calculations. The filtered neutron beams have a high purity and intensity at low contamination from the accompanying thermal, fast neutrons and γ -rays. The developed filters at energy (1.5, 2.0 and 7.5) keV in the present work allows a wide range application in BNCT because they have high intensity and purity at low contamination of generated γ-rays.