الفهرس 
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Abstract
Radiation shielding is matter of interest of different researchers and of public concern because of the development of nuclear technology and using this technology in various fields of medicine, industry and research. In fact, this technology is based on ionizing radiation, which has harmful effects on human health and environment. Therefore, radiation shielding involves the deliberate introduction of shielding material between the ionizing radiation sources and workers.
This work deals with the problem of suppressing neutrons and gamma rays, which may leak out from the radio therapeutic shelter room at medical therapy facilities, transporting the chemical isotopes and experimental nuclear reactor. For this purpose composites in the form of paste of high density polyethylene (HDPE), commercial borax (BX), sand and Portland cement (PC) were designed with different concentrations of each, which constructed and tested for (0.2 TBq - 241Am-Be) neutrons and (27.75 TBq - 60Co) gamma rays with energy4.5 MeV and 1.25 MeV respectively .
A series of specimens was prepared from composite materials. The composite was divided to seven composites namely, C1, C2, C3, C4, C5, C6 and C7. The samples that presented are a combination of seven different concentrations of HDPE and BX mixed with 25% sand and 25% Portland cement mixed with each other with suitable amount of water . The homogeneous mixture was formed in squire shape plates of 20cm side and 1.5 cm thick. A group of these plates samples was arranged together to form an assembly about 15 cm thick for the attenuation measurements for each composite. The volumetric density, the elemental composition, the bulk stress and strain of each composite are determined. Experimental and theoretical Calculation of fast neutron and gamma ray attenuation parameters have been carried out using a collimated beam of neutron and gamma rays, where;
Studies of the effective removal cross-section ΣR of fast neutron that gives information about the interactions that tend to remove energy from the fast neutron group.
Studies of the total macroscopic scattering cross section (Σt), slowing down power (Sdp) and moderating ratio (MR) for neutrons, which gives information about the attenuation of neutrons during their propagation through a medium.
Calculation of the tenth value layer (TVL) , half-value layer (HVL) and the relaxation length of the photon (λ), which gives information about the thickness of a given material needed to reduce the intensity of the incident radiation to 50%, 90% and 37% respectively.
Investigation of the linear attenuation coefficient (μ) and total mass attenuation coefficients (µ/ρ) for gamma rays at energies from 0.01 MeV to 100 MeV using a computer program WinXCom which describes the fraction of attenuated incident photons in a monoenergetic beam per unit thickness of a material.
The results proved that, there are agreement between the measurements and the calculated parameter. In addition, adding HDPE and BX enhanced the shielding efficiency but with different degree of attenuation and C6 has the most efficient properties as a shielding material as compared with the other composites demonstrated which, The HVL for neutron is 7.2 cm and for gamma is 6.5 cm.
Key Words:
New Shielding material; Attenuation parameters; Effective removal cross-sections; High density polyethylene; Borax; Composite paste; Mass attenuation coefficients; Fast Neutron; Gamma rays; Slowing down power; Moderating ratio.