مجله علوم و فنون هسته ای
سال سی‌ام شماره 2 (پیاپی 48، تابستان 1388)

Tokamak is known as a magnetic system for plasma confinement, where the plasma is heated and pressurized under the influence of powerful toroidal and poloidal magnetic fields. Currently, tokamak is one of the proper choices for generation of clean and low-cost energy, and it is anticipated that the construction of ITER as an international project in France fulfills the mankind dream for providing an economy energy resource. In this paper, we consider the equilibrium and transport problem in a tokamak plasma, and we study the numerical solution to the corresponding equations to achieve a desirable plasma configuration in Damavand tokamak, of electromagnetic fields highly elongated cross section. Through the self-consistent combination of transport and equilibrium equations, we obtain a scenario for the temporal and spatial evolutions of plasma in Damavand. In particular, we noticed from the study of simulation data the existence of separatrix configuration in a small tokamak with elongated cross section and large aspect ratio. The separatrix configuration is a characteristic of advanced tokamaks including JET, and is regarded as an essential capability of these machines. This paves the way for designing a divertor for Damavand tokamak, to study the plasma-wall interaction, as well as mechanisms of energy extraction from plasma.

Samarium-153 is one of the most widely used radionuclides in preparation of pain palliation radiopharmaceuticals of bone metastases. Therefore, it is important to realize the types and amount of impurities in the products. The aim of this study is to evaluate the produced impurities (154Eu, 155Eu & 156Eu) both theoretically and experimentally. These impurities are produced in 153Sm preparation by irradiation of natural samarium. In the experiment, the gamma spectra are recorded at different time durations, as the half-lives of impurities are longer than 153Sm half-life. Moreover, a comparison is also given to show that the results of the experiment and that of theory are in good agreement with each other, where it gives an accurate assessment of the amount and the type of impurities.

: In this experimental work, hard x-ray emission in Damavand tokamak along with the temporal evolution of plasma current and loop voltage have been studied for shots in which plasma current varies from 17 to 32kA. The time evolution of plasma current from beginning of the discharge to the disruption phase, loop voltage, and hard x-ray emission has been anlalyzed. The hard x-ray emission for the plasma current less than 20kA has been observed during the disruption phase, where the discharge duration is less than 10ms. For plasma current is more than 20kA, however, hard x-ray can be observed at the beginning to the disruption phase and it persists for 20ms. Two kinds of regimes can be realized for the runaway electron production in this tokamak. The first regime is similar to other tokamaks and takes place during the disruption phase. This regime is understood by Dreicer theory of runaway electron production. The second regime which is observed from the beginning to the end of discharge is related to the avalanche event.

Due to the importance of the effect of temperature variation on the scintillation parameters, such as the light output, energy resolution and scintillation efficiency, we intended to verify the temperature effect on the response function of the BGO and NaI(Tl) scintillators. For the gamma ray and charged particles detection, scintillators such as Bismuth Germinate Oxide (BGO) and Sodium Iodide activated by Thallium (NaI(Tl)) are widely used. Thus the effect of temperature variation on the scintillation efficiency, light output and energy resolution have been measured using both BGO and NaI(Tl) scintillators of Ø2”x2” and Ø3”x3” dimensions in the energy range of 600-1400 keV, and at the temperature ranging from -30°C to + 70°C. Since the photomultiplier tubes (PM) tubes and scintillators are connected together, it is rather difficult to study the temperature effect on the scintillator alone, so the effect of temperature change on  the PM tubes+scintillators was studied first. A similar study for the PM tube alone has been performed in a different experiment. By increasing the temperature, the scintillator efficiency and the light output decrease and the energy resolution deteriorate, whereas by decreasing the temperature, the light output and the scintillator efficiency increase and the energy resolution will improve.

Position sensitive detectors (PSD) are instruments that determine the position of the incident radiations. One type of these detectors is the gas flow proportional counter. Generally, position sensitive detector works in two different methods, so called charge division and rise time methods. In this paper, we explain our new method that is based on the gradual variation of the electrodes distance. Our results in this research show that the introduced method can be a good choice for determining the position of low energy radiations. In this counter, spatial resolution considered to be varying from 0.1 to 1mm along 15 centimeter of the active length.

In this paper performance of 13C molecular laser isotope separation is reported. For this purpose, a TEA CO2 laser pumped NH3 laser was constructed which provides output energies of 350-400mJ with a pulse duration of 100 ns at 12.812µm wavelength. The laser pulses were focused into an irradiation cell containing 0.1-1 mbar CCl4 gas pressure. Under the multiphoton dissociation condition of 12CCl4, a maximum selectivity of S=4 and separation factor of β=7 was obtained.

A polynomial nodal method is developed to solve few-group neutron diffusion equations in cartesian geometry. In this article, the effective multiplication factor, group flux and power distribution based on the nodal polynomial expansion procedure is presented. In addition, by comparison of the results the superiority of nodal expansion method on finite-difference and finite-element are fully demonstrated. The comparison of the results obtained by these method with those of the well known benchmark problems have shown that they are in very good agreement.

In this work the concentration levels of 226Ra were measured in 42 samples related to 14 types of bottled natural mineral water commercially available in market. The applied method for this measurement was emanation method with a minimum detection limit of 2 mBq l-1. After adjusting the pH below 2 by concentrated HCl, the radium was co-precipitated with barium and lead as sulfate. The precipitate was dissolved in alkaline EDTA (C10H14N2O8.2H2O) and placed in 20ml bubbler. The bubbler was sealed and stored for 21 days at 5oC for ingrowth of 222Rn. For calculation the committed effective dose for adults drinking 40 l y-1 of bottled mineral water, the ingestion dose conversion coefficients from the IAEA publications is used. Concentration of 226Ra ranged from 2.0 to 12.3 mBq l-1. In one case 12.3 mBq l-1 was measured, which provides 0.138 µSv committed effective dose for adults in the case of consumption rate of  40 l y-1.

The excitation functions of natAg(p,n)109Cd, natAg(d,2n)109Cd, natIn(p,pxn)109In®109Cd, natCd(p,pxn)109Cd and natPd(α,xn)109Cd reactions for 109Cd production were calculated using ALICE-91 code. The required thickness of the target was obtained by SRIM code for each reaction. The production yield of cadmium-109 was calculated by considering the excitation functions. The heat transfer of the target in each above mentioned nuclear reaction was investigated. The optimum reaction for production of 109Cd by accelerators was determined.

In order to transfer the geomagnetic and gravity data which are used in exploration of ore including uranium from an uneven surface (the surface of the earth) to a flat one, new designed softwares are introduced. By these softwares a better depth estimation of ores is provided. These softwares are Pinit and Unev2fla. The language used in producing these softwares is Fortran. The common upward and downward continuation methods are for transferring the data from a flat surface to another flat one, and are not useful for transferring the data from an uneven surface to a flat one. One of the methods that can be used in this regard is using Taylor series which are used as the algorithms of the softwares. Design and production of the present softwares, which are the results of this research, these softwares can be used in practical geophysics for a better depth estimation.