نشریه تابش و فناوری هسته ای
سال یکم شماره 3 (زمستان 1393)

With the development of nuclear technology in the world and the use of the technology in industry and medical centers¡ the countries in this category¡ and investment in this area has increased. Because of nuclear-radiation such as gamma and neutron radiation¡ and also such harmful to human health¡ in these centers to avoid irreversible effects of this type of radiation¡ shielding that must be made in addition to decrease of energy and intensity of this type of radiation¡ the economy well. In design of this type of shieldings¡ role of the structural concrete must also be considered. Therefore¡ in order to provide the two things mentioned¡ the mind is focused on researchers to produce concrete with protective properties. Concrete is a substance that has highest applicaton and consumption in the world after water. Production of concrete with protective properties can be a great service to humanity. In this study¡ we have tried to use the MCNPX code for identifying additiinal material such as boron and hydrogen¡ to produce concrete protective properties¡ and investigated the treat of this kind of concrete against neutron radiation by adding materials such as polyethylene and boron carbide . In this context¡ neutron sources of Department of Energy Engineering and Physics of Amirkabir University of Technology simulated and the results show a declining trend of neutron flux with increase of the percentage of polyethylene and boron carbide in concrete.

Recent researches show that the thermal column of TRR is an appropriate facility which can be modified for epithermal BNCT. The main need modification is to remove all graphite blocks from it but at present it is impossible. The most important challenge is the high gamma dose rate in the thermal column. The other alternative facility for BNCT is the TRR medical room. In this work an experimental and theoretical investigation on the use of this room for BNCT has been presented. The experimental investigation consists of (1) the possibility of operation of the reactor core in the open pool position, and (2) measurement of neutron energy spectrum near the eastern side of the reactor core. The theoretical investigation consists of MCNP Monte Carlo simulation to estimate the epithermal neutron flux at the patient position. Multi-foil activation method and SANDII unfolding code were used to measure the neutron energy spectrum. The MCNP simulation was consisted of the reactor core, medical room, reactor pool and a beam tube (between the core and patient position). The results show that in view of the technical aspects, the reactor core can operate in the open pool position. In an experiment the reactor core operate in this position for 20 min at 30 kW power. MCNP result shows that by considering a special in-pool BSA an appropriate epithermal neutron beam (~5×109 ncm-2s-1) could be achieved.

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.

Beta decay is one of the usual decay modes in nuclides and wide varieties of nucleus emit this kind of radiation naturally or in the mode of unstability. In this paper along with study the structure of 12Be, 12B and 12C based on the Mean Field theory and by using Woods-Saxon Potential as most authentic potential, amplitude of wave functions are investigated. Based on these wave functions, mixed states by considering of spin and isospins of states in Mean-Field theory are obtained and then beta decay rate of 12Be by using Fermi and Gamow-Teller transitions are calculated and compared with available experimental data in literatures. This comparison shows desirable agreement between experimental data and theoretical results.

In this paper, abundance percent of copper element in the soil sample provided from mine sungun of Ahar, is determined by activating it in front of an Am-Be neutron source and counting it's activity using 3 inch NaI(Tl) detector. For this purpose, first, a sample of copper powder (with a purity of 99%) is placed in front of the Am-Be neutron source in different distances and then it's activity is determined using NaI(Tl) detector in order to obtain the distance that maximum activity is achieved at it. Then, at this optimal distance, soil samples containing specific percentages of copper that we provided them precisely, are exposed to neutron radiation and their obtained activity is compared to activity that is obtained for standard sample and accuracy of analysis is calculated. Measurements show that using NaI(Tl) detector, one can determine abundance of copper element in soil with accuracy up to 0.2 percent.

In this paper, several prepared samples of copper and iron powder with a purity of 99% ,with various thicknesses of water, polyethylene and graphite moderators are irradiated in front of a isotopic Am-Be neutron source. Measuring the distance at which samples achieve the most amount of activity, the mechanism of neutron moderation in water, polyethylene and graphite moderators is investigated. Using obtained experimental results, maximum areas under the curve are plotted for each of water, polyethylene and graphite moderators. Comparison the plots related to iron and copper samples shows that the area under the peak for iron is much less than that for copper. This means that occurred nuclear reaction in iron sample is related to fast neutrons that has low cross section. This means that reactions related to fast neutrons have been occurred less than other neutrons. The reason for that is low cross section associated with fast neutrons that has been discussed completely in the paper.