الفهرس 
AcknowledgementOnly 14 pages are availabe for public view
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Abstract
The transport of photons through matter is described by a very complicated equation ,its solution either analytically or numerically are not practical One of the important approaches which simplify the transport calculations is the build up factor Using this approach a semi-analytic procedure for obtaining the flux at any point is possible , utilizing relatively simple mathematical expression Through this thesis a detailed calculations of the gamma ray build up factors by using the Monte Carlo method is carried out . The calculations are carried out for a planar normal source of gamma ray incident upon a three-layered medium taking into account all secondary photons produced due to the interactions of the primary incident photons with the atoms of the medium .
Important radiation responses have been investigated throughout this thesis the flux , dose rate energy spectra , the flux build up factor and the dose build up factor . These responses depends on the type of the material used , order of arrangement , initial photon energy and thickness of each slab , the dependence of the responses on its effective parameter are shown graphically. Another localized problem shown in this thesis is the effects of an inhomogeneity of lower or higher structured materials inside a homogeneous medium . Since the exponential form of gamma ray calculations relies on the accuracy of the build up factors, the present study uses the Monte Carlo method to calculate the build-up factors for the three-layered medium . The Monte Carlo method is considered as one of the most accurate methods , Besides, it can be very useful in explaining the physical phenomena governing the behavior of the radiation responses due to its ability to calculate any required internal information. The main disadvantage of the Monte Carlo method is its need for long computations times .