JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY
Year:2011 | Volume:- | Issue:2 (56)|Papers Count:9

High power pulses with low widths have many applications in radiation generator devices as flash radiography and high power microwave generators. One of the compression methods of high power pulses is magnetic pulse compression. In this paper a Tesla generator with saturated core which produces a 200k V voltage pulse has been designed and then the effect of saturation of the core in the compression of the output pulse using Proteus and CST EM Studio codes was studied. Our studies showed that with saturation of the transformer’s core, the magnetic permeability and hence the inductance of the transformer’s coils will decrease and consequently the frequency of current oscillations in the transformer will momentarily increase where it will result in the decrease of the output pulse width.

In this work the ratio of the 4th peak to the 5th peak of a LiF: Mg, Ti (TLD-600) thermoluminescence dosimeter has been used to estimate the gamma dose in a mixed neutron-gamma radiation field. The samples were first exposed to the known neutron and gamma doses from Am-Be and 137Cs sources. Then, the contribution of the gamma dose in the mixed field was changed from 20% to 52% of the total dose. For this purpose by employing a computer program based on Levenberg-Marquart algorithm, and by using thermoluminescence general order model for the glow profile deconvolution, the ratio of the 4th to 5th peaks was determined. Finally, the peak ratios have been related to the contribution of the gamma dose in the mixed neutron gamma radiation field.

In this research, radiation dosimetry was made through measuring free radicals induced in synthetic hydroxyapatite (HAP) using EPR spectroscopy. At the first step, the hydroxyapatite nano-powders were synthesized via sol-gel method. The produced powders were passed through a thermal treatment, weighted and packed. Then, the samples were irradiated at different dose rates using 60Co g-ray and 10MeV electron beam radiation at a high dose range. The EPR signal intensity of hydroxyapatite samples were measured at room temperature in the air. Subsequently, the variations of the EPR signal intensities were constructed as peak-to-peak signal amplitude and were compared with alanine and bone powder samples. The results showed that the EPR signal intensity of the HAP samples are several times higher than alanine and bone powder and are saturated at the higher dose rates in comparison with other species.

Polonium-210 (210Po)is a natural contaminant of tobacco and its products. Due to its volatility and inherent adsorption properties, 210Po is one of the major potential sources of human exposure through smoking. This paper reports measurements on 210Po and 210Pb levels in domestic as well as imported tobacco to Iran through a-spectrometry technique. The fate of 210Po radionuclide has been also followed from tobacco farm through curing procedure in factory. The activity levels of 210Po in Iranian domestic and imported cigarettes is found to be on the average as 38.4±0.8 mBq/g with a range of 30.3-51.3 mBq/g and 20.0±0.6 mBq/g with a range of 18.6-21.7 mBq/g, respectively. These levels are considerably higher than those reported in many other parts of the world. In the case of tobacco produced in Iranian northern province of Guilan, drying in closed compartments by fossil fuel and elevated inventories of 210Po in soil due to over application of phosphate-rich fertilizers seems to be the main causes of these elevated activity levels.

In this paper, biosorption of uranium (VI) from aqueous solution by Cystoseira indica brown alga was studied in a continuous packed bed column. The experiments were performed at room temperature and pH 4. The uptake capacity of uranium ions was investigated by Ca-pretreated biomass in a flow rate of 2.3 ml/min, superficial velocity of 1.3 cm/min, and different influent concentrations. The results showed that by increasing the influent concentration from 30 to 120 mg/l, despite increasing the uptake capacity from 266.61 to 371.39mg/g, leads to reduction of the metal removal percentage. The experimental breakthrough curves were analyzed using Thomas, Yoon & Nelson and dose-response models. The investigations showed that these models are suitable for the breakthrough curves prediction.

Different researches have been performed on natural exposure of cosmic rays and their effects on the human health. Monitoring of cosmic derived gamma ray exposure of aircrews and passengers is the subject of the current study. In this paper, the controlable variations of the cosmic ray flux in the atmosphere and the cosmic radiation exposure at flight altitudes will be discussed. For this study, the exposure rates to gamma ray, in an energy range of 50 keV-1.5 MeV, for the Tehran- Bandarabbas air flights have been measured. The results show that the maximum dose rate at 3000ft (about 9km) is 15-20 times higher than on the ground base. Also, the dose rate for this pathway is about 1.87 mSv/h which for 500 hours flights per year it is estimatal to be 935 mSv. This number is less than human permissible dose rate of 1 mSv/year.

In this paper, a calculation for fresh fuels gap conductance at different axial lengths of fuel assemblies of the VVER-l 000 type reactors has been made using two models of Calza-Bini and Relap5. By applying these two models, the dependency of the fuel outer surface temperature and the clad inner surface temperature of the gap conductance has been determined upon using following procedures: Coupling gap conductance model computer programming to obtain temperature at different axial lengths of the fuel and clad; and coupling gap conductance model to the COBRA-EN output code. The results of calculations and comparison with the FSAR results showed that the Relap5 model is less accurate than the Calza-Bini model. The Calza-Bini model agrees well with the FSAR results. By combining these two models, a new model with a better accuracy was proposed for the gap conductance.

The Spent Fuel Assemblies (SFAs) of WWER-1000 reactors are planned to be transported by special containers which are supposed to be designed in a manner to stand against vibrations and impacts in order to protect the spent fuel from any possible damage. The vibration opposition of these containers shall be far beyond the critical resonance, because the resonances about the natural frequency of the structure will cause the enhancement of its oscillation range and may end with its disintegration. Determination of the amounts of natural frequencies and their mode shape can be achieved by vibration analyzing methods. The amount of the natural frequency of any structure crucially depends on its shape, material and lean points as well as the amount of the loads and the type of these loads. Due to the fact that the Spent Fuel Casks used for transportation in nuclear power plants in Russian Federation are TK-13 type and the pieces of information released are negligible, the scientists in Russia are working on the design and analysis of a new type made up of composite Material. In the presented paper the cask of spent fuel ofTK-13 is modeled by ANSYSâ 10.0 and ten natural frequency modes have been calculated, followed by the comparison of this result with the composite cask.