JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY
Year:2019 | Volume:40 | Issue:89 (3) |Papers Count:17

Pulsed laser ablation in liquid solution is a fast, safe and clean method for producing colloidal nanoparticles with different structural and optical characteristics. However, the other synthesis methods require high temperatures, long reaction times and multi-step chemical synthetic procedures. In this paper, the simulation of nanosecond pulsed laser ablation process and effective parameters on the Titanium, Silicon, and Tungsten elements in distilled water environment at the height of 1 cm from the surface of the metal is investigated. For this purpose, the pulsed Nd: YAG laser with nanosecond time duration, wavelengths of 1064nm and 532nm, a focal diameter of 200  m is used. The simulation is based on considering the effects of the water environment and number of laser pulses. The distribution of temperature on the metal surface and the threshold fluence is determined by two-fluid heat transfer model using Comsol Multi physic Package.

In this study, a Compton camera imaging system containing several scatterer layers made of Si and a LYSO detector as an absorber layer were designed and simulated using Geant4 code. At first, the efficiency of the system according to the number of scatterer layers was optimized using a gamma point source with various energies. After finding the best structure of the system which contains 10 layers of scatterer, two similar setup of Compton camera were placed perpendicularly to the proton beam around the phantom to take image of the position of the prompt gamma emission resulted from the nuclear interaction of the proton beam with the phantom. In order to imaging the gammas, information such as interaction positions and deposited energies in the scatterers and absorber were recorded by Geant4 code in a root file. Then, using a Compton camera reconstruction algorithm, production position profile of gammas was reconstructed in a MATLAB software. A Comparison of the gamma photon distribution and dose distribution showes that this Compton camera structure is able to measure the proton beam range with less than 7 mm error, which proves the capability of prompt gammas detection for verification of the proton beam range during proton therapy.

Regarding the importance of the stability in a miniature pinch plasma generator in repetitive and strong plasma pinch, the stable operation of a 3J miniature plasma focus device in two single-shot and repetitive discharge modes (at 0. 5Hz and 5Hz discharge frequencies) and the factors in creation of switch misfire was demonstrated. Then, the device efficiency and strength of the plasma pinch for four different coaxial electrode configurations were studied, upon scanning argon gas pressure ranged from 0. 6 to 1. 5 mbar via the study of the charging voltage variation from 8. 3 to 9. 3 kV. It was observed that the strength and efficient pinching is appropriately produced for the tapered anode configuration over an expanded operating pressure ranged from 0. 6 to 1. 5 mbar. After the calculation of the speed factor and pinch sensitivity for the optimum electrodes geometry, it was shown that the best plasma compression at the pinch phase was associated with 0. 88± 0. 8 mbar argon gas pressure and 8. 3-8. 5 kV charging voltage, respectively. From the viewpoint of the stability assessment of the device, it was observed that the stable operation of the device was for the charging voltage of 8. 3 to 8. 7 kV in the operating pressure of 0. 6 to 1. 1 mbar.

The effect of the coherence time of X-ray laser pulses on the population transfer in 97 Tc with two ground states and one excited state is investigated. In this study, two X-ray laser pulses drive the population transfer in a nuclear three-level system via the quantum optics technique of the stimulated Raman adiabatic passage. The short wavelengths, which is needed to satisfy the resonance conditions, are achieved by using an accelerated nuclear beam, interacting with two incoming X-ray pulses. It is found that the transfer efficiency decreases for laser pulses with short coherence time. Finally, the effect of laser pulses intensity and pulse delay variations on the population transfer for different coherence time values of laser pulses is studied. For the numerical study we have used the Master equation. The decoherence effects that occur due to spontaneous emission of the excited state and short coherence time of X-ray laser pulses (dephasing) are considered in the Master equation.

In this paper, the new Nano-structure of Germanium disulfide (GeS2) was forecasted using Wien2k computing software by the method of density functional theory (DFT). The stability of the nanostructure was confirmed by cohesive energy calculation as well as the phonon dispersion calculation. The results of the simulation approach show that the GeS2 monolayer is an indirect band gap semiconductor with a band gap of about 0. 9 eV, which is adjustable by a two-dimensional stretching and strain. Besids, the study of the properties of the optics of GeS2 showes that it has minimal absorption and reflection in the visible region of the electromagnetic spectrum, while the GeS2 in the ultraviolet region of the electromagnetic waves is not only a good absorbent but also has a relatively high reflection. The results of this study suggest that the considered structure (GeS2) has a good application in the new generation of the opto-electronic devices, especially as a UV protection layer.

In this paper, TEA CO2 laser pulses focused by plasma shutters with 2. 5, 5, and 10 cm focal lengths lenses were used to generate optical breakdown in various molecules having 1-5 atoms. Moreover, the dependence of the transmitted pulses temporal trace and the sparks geometry on the focusing power, as well as, the gas pressure, molecular weight, and ionization energy were investigated in detail. It has been observed that instead of the complete removal of the tail part in the transmitted pulse shapes, sometimes a fraction of them disappeares. For instance, the quenching time gap which is in the 0. 05-2. 6 µ s range appeares in the transmitted pulse shapes for the 2. 5 cm focal length. Such a quenching time at the lower scales, is also observed for He gas with the other focal lengths. The analyses of the generated plasma plume shapes and the focused laser beams paths reveales that this behavior is due to a quick dropping of the plasma density below the critical level before the pulse tail is completed.

In this paper, the interaction of femtosecond laser pulses with BK7 glass is investigated. A Ti: sapphire femtosecond laser with the chirped pulse amplification is used. By studying the diameter of the ablated area, the threshold fluence for the 40 femtosecond pulses at the 800 nanometers is obtained to be around 2. 7 J/cm 2. By moving the position of the laser focus into depth of the glass, and by changing the translation speed of the femtosecond laser pulses, depth of the glass has been micro machined by laser pulses. By using CCD camera pictures, obtained from propagation of the He-Ne light through the micromachined region, effect of the interaction with three different translation speeds, 0. 01, 0. 02 and, 0. 05 mm/s is investigated. The results show that the diffractive grating is formed inside the volume of the glass due to the interaction of 10 femtosecond laser pulses having 0. 35 microjoules at each position. Finally, the created diffraction grid step is obtained about 4. 52 micrometers.

In this research, the oxidation resistance of pure Ti3SiC2 MAX phase that produced via infiltration of porous TiC preform, fabricated by the gel casting process, was evaluated via oxidation at different temperature of 500, 800, 1000, 1100, 1200, 1300 and 1400 o C under the oxygen atmosphere. The oxide phase composition on the surface of the samples was characterized by X-ray diffraction analysis. The thickness of the oxide layers on the surface was measured on the cross-section of the samples using scanning electron microscopy (SEM). To investigate the oxidation mechanism, the TG and DSC thermal analyses were carried out in the range of 25-1500 ˚ C. The results showed that the high weight gains were not occurred up to 1000 ˚ C, and the oxidation procedure was accelerated for the temperature above 1000 ˚ C. The oxidaton reached a steady-state above 1400 ˚ C. The results of the oxide layers thickness measuements showed that by increaseing temperature to 1400˚ C, the oxide layer thickness increased to 121 µ m.

In this paper, using a new combinatory meshing technique in the axisymmetric coordinate, a MCC-DSMC solver is introduced. Using this solver, the flow and the concentration variation inside a centrifuge machine in a rigid body rotation mode with the DSMC method for a variable hard sphere and a variable soft sphere models and for the mixing hydrogen, argon, and krypton gases are investigated. Our results are compared with the analytical solution. The results indicate that the two collision models are totally in agreement with each other, but the results have some differences with the analytical results obtained from the Boltzmann distribution function. The results show that the presence of the several gases with different molecular weights in a centrifuge shaped a multi-layered radial flow of gas inside the rotor, so that the heaviest gas in the area of the side wall of the rotor, the lightest gas in the region near the axis of the rotor and gases with the medium molecular mass were placed in a layer between them. Furthermore, the variation of the concentration for each component of the mixing gas in the axial direction is also investigated by the DSMC method, otherwise, that it is impossible to investigate it using the analytical solution of the Boltzmann distribution function.

The microbial reduction and precipitation of uranium using anaerobic bacteria are one of the effective methods considered during the last two decades to prevent permeation of the uranium to the environment. In this study, the capability of a facultative anaerobic bacterium, Shewanella sp GCWx8, for reduction and removal of the uranium from the aqueous solutions are investigated. Thus, uranyl acetate is introduced into the bacteria anaerobically in the presence of the sodium lactate as an electron donor. This process resulted in the removal of the uranium from the solution and the formation of a precipitate containing uranium and cells. The analysis of the precipitate, using both Auto-lab and UV-vis spectra, confirmed that most of the uranium in the precipitate was in the from of reduced uranium, U(IV). Therefore, the mechanism of uranium removal by the strain GCWx8 in the aerobic condition is a reduction process. The best pH for a uranium removal by the GCWx8 was obtained 6. 8, and the maximum removal percent at the cell density of 10 9 (cells per milliliter) has gained 90%. The first order of the reaction rate was satisfactory for bioreduction at the first day of the incubation. Based on the first order of the reaction rate assumption for the uranium bioreduction, the reaction rate constant was obtained 0. 06 hr-1. As a result, strain Shewanella sp GCWx8 was found as an able bacterium for the uranium bioreduction.

In the feasibility studies used for the correct use of this side product, it was decided to investigate the effect of this substance in a light concrete. Due to the low specific gravity, the lightweight concrete is less resistant compared to other concretes. So, in this study, the effect of nanocrystalline silica nano and micro and macro silica fibers, a mineral extracted on the mechanical properties of light concrete, including the compressive strength and tensile strength, were investigated. The results showed the improvement of the mechanical properties of the light concrete for the use of nano silica to 4% cement weight. By combining nanosilica with micro silica and its effect on the mechanical properties of concrete, we found that the highest compressive strength was in using 2% nano silica and 8% micro silica. However, the combination of the nano-silica with a percentage of more than 8% of micro silica reduced the mechanical properties of the sample. Also, the mixing of macro-silica in concrete up to 25% increased the tensile and compressive strength.

Synthesis of 14 C-labeled organic compounds is being required by the medical, pharmaceutical, agricultural, industrial, and research centers. The Carbon-14 is essential for the tracking and recognizing the mechanism and performance of the synthesized chemical compounds. The Dihydropyridine is synthetically labeled with Carbon-14 in this work to pursue a further study about the mechanism of its action and to support the current metabolism. Therefore, to clarify further the mechanism of its operation and to support the current research on its metabolism, there is a need for the analogs of these compounds that are Carbon-14 labeled in a biologically stable site. The 1, 4Dihydropyridine channel blockers are clinically significant antihypertensive drugs and have been immensely valuable as molecular tools to probe into the structural and functional aspects of the channel function. In this study, N-Phenyl-3, 5-Dicarboxylate-2, 4, 6-Triphenyl-1, 4[ 14 C]-Dihydropyridine, which is a new compound of the Dihydropyridine derivative and had labeled with the Carbon-14, was synthesized. This novel synthetic compound having an N-Phenyl derivative is one of the new drug metabolites that have anti-cancer properties. Using a multicomponent reaction with the shortest stage in the preparation, separation, and purification, as well as, suitable conditions with an encellent radiochemical yield was developed.

In this paper, the effect of plasma density ramp and laser pulse length on the energetic particle generation and pulse scattering were investigated in an under-dense plasma for short and long pulse lengths, of τ L = 60 fs, and τ L = 300 fs, respectively. In our simulations, we used a kinetic particle in cell simulation 1D-3V code. It is found that the laser pulse length and density ramps play an important role on the energetic particles generation and pulse scattering in plasma. So that, the simulations of the laser pulse length impact indicate that, in the case of short pulse interaction with the under-dense plasma, electrons are accelerated to the higher energy level. Furthermore, among the three different ramps: steplike, ramp 1 with a steep slope, and ramp 2 with a gentle slope, in the case of the step-like density ramp, electrons accelerate to high energies, in comparison with two other ramps. A fourier analysis of the total radiation spectrum indicate that in the case of the step-like density profile, the growth rate of the electromagnetic modes have maximum regular picks and minimum growth rate obtained in the case of the smooth ramp. Meanwhile, the time evaluation analysis of the energy distribution function shows that with the time increment of the pulse propagation, in the shorter pulse case, and for the step density scale length, plasma particles can reach a high energy level.

This paper tries to find a suitable probability distribution function for the optical density of the welding lines in the radiographic films. For this purpose, real gamma ray radiography films of the oil and gas pipelines were used in the operational areas of the National Oil Company. The number of the radiographic films was 4 and due to the unpredictability of the radiographic conditions and the existence of different regions on the surface of the films, histogram curves of the scattered data were selected to this investigation. More than 36 probability distribution functions were fitted on the histograms. 11 fitted probability functions with R-sq. ≥ 0. 95 were selected among the total functions. In addition, the final selected functions were fitted to 4 internal concavity (Suk Back) defects. Based on our obtained results, the best function was Pearson IV. Although a Gaussian function was also fitted and behaved quite well, but it was found that it is not perfect.

This paper presents the design of a thermionic electron gun with two different geometries, flat cathode and spherical cathode. The purpose of this research is to answer the question of which type of electron gun is suitable for industrial electrostatic accelerators. CST Studio software was used to design the guns. The desired specification in the design of a suitable thermionic gun, the maximum current of 50 milliamper and the voltage 5 to 10 kilovolt, is selected for use in the dynamitron accelerator. The beam current, the waist beam radius, the waist beam position and the perveance of a flat cathode gun and spherical cathode gun were 49 and 49. 8 mA, 3. 2 and 0. 45 mm, 36 and 24. 3mm, 0. 138 and 0. 0498 μ perv, respectively. Since the electron guns used in the industry have a perveance between 0. 1 to 1 μ perv therefore, an electron gun with a flat cathode with 0. 138 μ perv is more suitable. On the other hand, it is easier and less costly to make it. That is why the gun with a flat cathode was chosen and its final dimensions are presented.

To perform an effective experimental implementation in a zero-power reactor or more generally, critical assemblies, it is necessary to measure the total neutron flux to calibrate the reactor power. The 4π β-γ coincidence method via the activation of gold foil is a well known standard method for absolute neutron flux measurements. The absolute neutron flux is obtained by measuring the absolute activity of the irradiated gold foil, ranged in 10 2 4-10 Bq. In this method, the gold foil is irradiated at the desired position. The beta, gamma, and the coincidence rates are by using the 4π β-γ coincidence system, and the absolute activity of gold foil is then obtained. The β-γ rays emitted from the irradiated gold foil are recorded in a concise period of tim (of the order 10-8 seconds). The advantage of this method is that the efficiency of either detector is directly dependent on the counting rates. Changing the beta detector efficiency due to the high voltage change and then measuring the beta, gamma, and coincidence counting rates, the plot of beta counting rates against the beta detector efficiencies can be introduced. By extrapolating the efficiencies to a unit value, the absolute activity of the gold foil can be obtained.