Investigation of gama radiation behaviour in building materials

Besides background radiation due to long-lived natural radionuclides resides in earth or cosmic radiation from outer space, artificial radiation affects human life in an increasing manner. After the discovery of radiation it becomes more and more important in human life. Today it has a wide range of use in many areas, such as medicine, industry, agriculture etc. In this manner certain precautions, one of them to be shielding, has to be taken not only for radiation workers but for the public. Radiation shielding materials are investigated for their shielding properties through linear attenuation coefficient (μ) being defined as the probability of interaction of radiation with matter in unit path length. Linear attenuation coefficient of a material for a given specific gamma energy can be determined both experimentally using narrow beam geometry and computationally by using XCOM. In literature building materials was studied by many scientists in terms of their gamma shielding properties. In this study, some building materials regularly used in Turkey, such as concrete, gas concrete, pumice and brick have been investigated in terms of mass attenuation coefficient at different gamma-ray energies. These building materials were supplied from a private building companies. The coefficient μ depends on photon energy and on the material being traversed. The linear attenuation coefficients have been evaluated comparing N and N0, which are the measured count rates in detector, with and without the absorber, respectively. The mass attenuation coefficient μmass is obtained by dividing μ by the density ρ of the material. The effectiveness of gamma-ray shielding is described in terms of the half value layer (HVL) or the tenth value layer (TVL) of a material. The HVL is the thicknesses of an absorber that will reduce the gamma radiation to half, and the TVL is the thicknesses of an absorber that will reduce the gamma radiation to tenth of its intensity. HVL and TVL can be calculated by using the linear attenuation coefficient (μ). The linear attenuation coefficients of building materials were measured using the portable NaI(Tl) detector (FLIR identiFINDER UW). Lead collimators were prepared for the gamma rays to be collimated through a hole of 7 mm radius and to avoid scattered radiation reaching to the detector. Narrow beam gamma-ray transmission geometry was used for the attenuation measurements. Cs-137 and Co-60 gamma ray sources which produce gamma ray energy of 662 keV, 1173 keV and 1332 keV were used in this study. For each thickness of a material, 9 measurements of 120 seconds for Co-60 and 60 seconds for Cs-137 were obtained. The average of these 9 measurements was used for both attenuated and unattenuated beams. After calculating standard deviation of these statistics, error percentages were calculated, which were less than %2.0 for Co-60 and %0.9 for Cs-137. The linear attenuation coefficients were also calculated via calculation of the mass attenuation coefficients which were obtained using XCOM computer code. The chemical composition of these materials, which were necessary input for XCOM calculations, was obtained from XRF analysis. According to the results, linear attenuation coefficients decrease with the increasing photon energy for these materials. This is due to the different photon absorption mechanism for different photon energies. The results shows that while smaller thickness of concrete is required to stop gamma-rays, larger thickness is required for gas concrete to stop same energy photons. It is easier to stop low energy photon than high energy photons. From the present study, it was found that among the investigated building materials, concrete appears as best gamma ray shielding material due to its higher values for mass attenuation coefficient. Experimental results were also compared with the calculated results (XCOM code). The calculated and measured linear attenuation coefficients show good agreement with literature.