Study of -ray energy losses in the ionic crystals using Monte Carlo code

In this paper, measurements were carried out of the calculated attenuation of the ranges gamma rays energy(279,356,479,662) KeV and using radioactive sources (Hg 203 , Ba 133 , W 189 , Cs 137 ). In the current results has determined (μL, μm) by using Monte Carlo simulation (i.e. through the account of each of the intensity falling and intensity transmit in samples proposed in search ) .permission has been drawing relationship graphs between the logarithm of the absorbance and thickness proposed for each of the ionic crystals (CsI, CdTe), hence slope graphs relationship represents attenuation coefficient linear and thereafter are calculated attenuation coefficient mass through during the relationship the following (μm = μL / ρ), and the results showed the current search using the Monte Carlo that the values of coefficients mass attenuation of gamma rays in crystals (CsI, CdTe) converge and overlap with each other at high energies the fact that the attenuation depends vitally on Compton scattering , either the values of attenuation coefficients linear showed a variation the obvious fact that the attenuation coefficient depends on the density of the absorbed . Addition, the study was examine to calculate the total atomic cross section and electron density, and the results of this study showed good agreement with the XCOM package.


1.INTRODUCTION
Ionic Crystals are a class of crystals in which the lattice -site occupants are charged ions ,.They are perhaps the simplest type of chemical bonding to visualize since it is almost totally electrostatic in nature [1].The criterion for such bonding is the difference in electro negativity, and as such occurs between electropositive elements and electro negativity elements (generally electropositive elements from group I or II and electro negativity elements from group VI or VII Hubbel reported ( ) values for 40 elements and 45 mixtures and compounds over the energy from (1KeV-20MeV) [4].Gamma -ray attenuation coefficients have been determined experimentally using a narrow beam transmission method for PbO-SiO 2 glasses system at 662,1173 and 1332 KeV photon energies [5].Determine the mass attenuation coefficient for members of BaO-B 2 O 3 glass system at various energies in the 356-1332 KeV range [6].The mass attenuation coefficient is a fundamental factor to derive interaction parameters of diametric and shielding interest such as molecular ,atomic and electronic cross sections ,effective atomic number ,electron density ,energy deposition and shielding effectiveness [7][8][9].The photon interaction with matter is combination of partial interactions namely photoelectric absorption ,Compton scattering and pair production .The mass attenuation coefficients of individual elements are being employed XCOM program in energy (1KeV-100GeV) [10].Scattering and absorption of is related to the density and atomic numbers of an elements. In composite materials, it is related to the effective atomic number ( and the electron density ( ,a single number cannot represent the atomic number uniquely across the entire energy range ,as the partial interaction cross -section have different atomic number, Z, dependence [11].

2.MATHMATICAL BASIS a) Mass attenuation coefficient:
As a photon makes its path through a matter there is a probability that it makes an interaction with the material such as absorption (photoelectric effect) , scattering (Rayleigh or Compton scattering ) or splitting (pair production ).Therefore ,part of the incident beam of intensity ( ) will be partially or completely removed from the beam as a result of interactions within the absorber of thickness x,this reduces the transmitted intensity that reaches the detector to ( ) ,where ,introducing the linear attenuation coefficient ,the transmitted intensity is given by ; This called the Beer -Lambert law ,where ( ) measured in units of length -1 describes the probability of absorption or scattering occurring per unit length within the absorber material [12].The exponential means that equal thickness of the absorber attenuates the photon beam by an equal fraction or percentage [13]. The total mass attenuation coefficient (μ/ρ)C for any chemical compound or mixture of elements is given by mixture rule [14]; where Ai is the atomic weight of the ith element and ni is the number of formula units.

b) Cross section :
The cross-section can be defined as the probability of an interaction to occur, it has the dimension of area in units of barn abbreviated b = 10-28 m2 = 10-24 cm2 = 100fm2.There are different kinds of cross-sections; atomic, molecular and electronic cross-sections, the atomic cross-section for an element of atomic weight A is given by: represents the Avogadro's number. For a compound the molecules of which have ni atoms for the i-th element, the atomic or molecular cross-sections are given by:

∑ ∑
The electronic cross-section for an element is given by: Hence, for the compound, the electronic cross-section is The effective atomic number is equal to: The electron density can be defined as the number of electrons per unit mass, and it can be mathematically written as: where N el represents the electron density in unit of electron/gram, (μ/ρ) c is the compound mass attenuation coefficient and σ e is the electronic cross-section.

Figure (5):
Illustrates the exponential relationship between the linear attenuation coefficient and the photon energy of ionic crystals calculated by the Monte Carlo program and XCOM package.

C) Calculation total atomic cross section and electron density:
Measured total atomic and electronic cross section for ionic crystals were presented in Table   (