1 Theory of absorption of gamma rays on the surface of SiO 2 nanopowder and SiO 2 -H 2 O nanocomposite Elchin Huseynov The Institute of Radiation Problems of ANAS, AZ 1143 B.Vakhabzadeh 9, Baku, Azerbaijan elchin55@yahoo.com Lu Jin China Institute of Atomic Energy P. O. Box 275, Beijing 102413, China panlujin@gmail.com Abstract We have theoretically investigated gamma rays absorption on the nanosilica surface. Calculations revealed that absorption of gamma rays was observed not only on the surface, but also inside of SiO 2 -H 2 O nanocomposite and SiO 2 nanopowder, because radiation effects of selected nano- particles more than the macro-particles. If the system gets 20000 photons; 0,0576 photons absorbs in 20nm thickness (this is same silica nanopowder diameter), 2, 879796797 photons in 1μm thickness and 2682,24863 photons in1mm thickness. Nano silica has more surface, therefore, more surface effects and absorption of gamma rays on the surface has got in this sample. We also take out specific equation for absorption gamma ray on the nanosilica surface. We have investigated the effects of secondary electrons and photons emitted from surrounding materials on defect formation in silica nanopowder under γ-ray irradiation. PACS: 61.46.Df; 41.60.-m; 78.40.-q; Keywords: Nanosilica, silica nanopowder, radiation effects, nanotechnology, γ-irradiation of SiO 2 1. Introduction “Gamma rays” is the name given to high energy electromagnetic radiation originating from nuclear energy level transitions. In this case typical wavelength, frequency, and energy ranges are: 0.0005 to 0.15 nm, 2 × 1018 to 6 × 1020 Hz, and 10 keV to 2.5 MeV, respectively. The terms gamma rays, nuclear x-rays, and high-energy photons are often used interchangeably. Gamma rays traversing matter are absorbed due to a number of processes. The ability of a substance to absorb gamma rays is expressed by the absorption coefficient for that substance. In this experiment an attempt will be made