Radiochim. Acta 2018; aop Maryam Amini*, Alireza Vejdani Noghreiyan, Zahra Dehghani and Mohammad Hossein Majles Ara Effect of gamma irradiation on the structure characteristics and mass attenuation coefficient of MgO nanoparticles https://doi.org/10.1515/ract-2018-2924 Received January 6, 2018; accepted April 16, 2018 Abstract: In this work, the structure properties and mass attenuation coefficient of MgO nanoparticles were studied before and after gamma irradiation. The as-synthesized samples of MgO nanoparticles by sol–gel method were analyzed by XRD which suggested the double phase; cubic and hexagonal structures of the material. Crystal defects produced in the cubic and hexagonal lattice were studied before and after exposure to 20 kGy gamma irra- diation in order to investigate the changes in the struc- ture properties and mass attenuation coefficients of MgO nanoparticles. XRD data of gamma-irradiated and non-irradiated MgO nanoparticles show that the crystal size of MgO nanoparticles increases after radiation expo- sure. SEM images after irradiation indicated significant changes in the morphology. The UV-Visible absorption spectra of the nanoparticles were taken and the results of optical band gap of the MgO nanoparticles before and after irradiation show that the value of band gap has changed slightly due to gamma irradiation. The results of comparing experimental values of mass attenuation coefficient for non-irradiated MgO nanoparticles with theoretical values of mass attenuation coefficient for MgO microparticles calculated using the NIST XCOM show that the mass attenuation coefficient not only depends on the effective atomic number but also depends on the size of the particles. Also, it is observed that the mass attenua- tion coefficient of MgO nanoparticles decreases after the irradiation which shows that by increasing the size of the nanoparticles, the mass attenuation coefficient decreases. It could be because the cross-section of photon interaction with materials depends on the surface to volume ratio of nanoparticles. The experimental results also show that the linear and mass attenuation coefficient of MgO nano- particles decrease with increasing the photon energy. Keywords: MgO nanoparticles, structure properties, mass attenuation coefficient. 1 Introduction Although using the gamma radiation has an important role in science and technology, the human exposure to high level of gamma radiation can lead to cancer by dam- aging the DNA located in the cells of the human body [1]. Shielding against radiation is one of the effective methods used to protect people from harmful effects of radiation exposure by lowering the intensity of gamma radiation to a desired level [2]. When gamma rays pass through the matter, the absorption probability is proportional to the density, thick- ness and gamma absorption cross section of the material [3, 4]. A basic quantity shows the ability of material to attenuate gamma rays is the linear attenuation coeffi- cient (μ). It describes the fraction of absorbed or scattered gamma rays in a narrow beam of mono-energetic photons per unit thickness of the absorber material. This quantity depends on the energy of the incident gamma rays, atomic mass number and density of the shielding material. Since the linear attenuation coefficient is a density dependent quantity, the mass attenuation coefficient is often used instead. Mass attenuation coefficient (μ m ) is a density independent quantity defined as the linear attenuation coefficient per unit density of the material [5]. Common forms of shielding include rigid materials such as lead bricks and high density concrete with limited portability [3, 4]. In recent years, several experimental and theoretical works have been done in order to evaluate mass attenu- ation coefficients of various materials [6, 7]. Gamma and neutron shielding properties of several concrete materials *Corresponding author: Maryam Amini, Department of Physics, University of Neyshabur, P. O. Box 9319774400, Neyshabur, I.R. Iran, E-mail: m.amini@neyshabur.ac.ir Alireza Vejdani Noghreiyan and Zahra Dehghani: Department of Physics, University of Neyshabur, P. O. Box 9319774400, Neyshabur, I.R. Iran Mohammad Hossein Majles Ara: Department of Physics, Kharazmi University, Tehran, Iran Brought to you by | York University Libraries Authenticated Download Date | 6/6/18 8:48 AM