فهرست مطالب محمد نیکوصفت

The surface modification of St37 steel irradiated with two different plasma regimes was investigated and compared. At first, using a plasma focus device, the interaction of high-energy nitrogen ions, colliding with the specimen in a pulsed manner (in nanosecond time scale) was studied. Then, the interaction of nitrogen ions with the specimens in the glow discharge plasma regime was investigated. Using SEM, EDS and XRD Analyses the morphology changes of the samples were studied. The SEM images show that small, dense and abundant bubbles (about 100 nm) were created by the pulsed plasma source on the surface of the specimens. On the other hand, the glow discharge plasma has created blisters with a size between 0.5-2 micrometers on the surface of the samples. The XRD results indicate the chemical reaction of nitrogen ions with iron in the glow discharge plasma regime. Also, the Vickers hardness test results illustrated that the hardness of the samples increased significantly.

The scattering of gamma photons backward from the surface of a material is named as backscattering of gamma rays.in this study, to evaluate the gamma backscattering, various shield of lead, aluminum and iron in the disk form of approximately 0.1 cm thick and a diameter of 18 cm were prepared. There is also a gamma source of cesium 137 were placed between the shield and NaI(Tl) detector and gamma spectra were recorded. In order to study the effect of the thickness of the shield in the amount of gamma backscattering, so at each step of the experiment 0.1 cm thick shield are added and every time the gamma ray spectrum is enrolled and It was observed that change the thickness of the panel is cause to change behind area of the maximum level backscattering (that it can be seen in Approximately energy of 0.250 MeV in the energy of Spectra recorded gamma) and in a certain thickness that has the name saturated thickness the backscattering reach to the maximum possible.