simulation

The feasibility of producing the iridium-192 radioisotope has been investigated in this work. Iridium-192 has various applications in nuclear medicine, particularly in brachytherapy. To increase the production yield and the high purity of this product, the direct production parameters of this radioisotope were studied based on the 191Ir (n,γ) 192Ir reaction. It is crucial to determine the appropriate irradiation location according to the neutron flux and the cross-section of the neutron reaction with the target material. By analyzing the experimental spectrum of neutrons exiting the reactor, as well as simulating the reactor using the MCNPX code, detailed information was obtained on the flux and spectrum of thermal neutrons and the irradiation sites. Calculations related to the flux of thermal neutrons were performed both theoretically and through simulation. Considering the information obtained from the simulation and comparing it with the experimental diagram of the reaction cross-section, the optimal irradiation site for the production of iridium-192 was determined. By comparing the simulation results related to the final activity at different reactor locations, the best site for producing iridium-192 with the highest activity was also identified.

Inductively coupled plasma (ICP) is widely used in applications such as material processing and In this comparative study, we aim to design a dielectric barrier discharge (DBD) reactor under atmospheric pressure. The current requirement is to characterize the plasma and optimize the designed plasma system under variable circumstances. A one-dimensional time-dependent simulation of a DBD tool, driven by a sinusoidal RF voltage with an amplitude of 755 kV at 52 kHz, in argon gas is shown. The DBD device with two electrodes, covered by dielectric material and with variable dielectric constant between 2, 5 and 8 was considered, and the discharge parameters were simulated in terms of time across the plasma space to find an optimal dielectric constant for delivering maximum power deposition. Using a sinusoidal voltage to DBD device with different dielectric constant, electric field profiles, electron density, electron temperature, mass fraction of argon atoms, average electron energy, ion current density, electron current density, plasma, and power deposition are shown.

Nowadays, by expanding the application of thin layers in industry and medical sciences, their fabrication methods have also received attention. One of those methods is the vaporizing material method with the help of an electron gun. The most important part in the electron gun is the electron optic, which is responsible for producing and accelerating electrons, so that it becomes possible to vaporize refractory materials in a shorter period of time by better modifying and controlling the electron beam (the shape and diameter of the electron beam) at the target location. The reduction and control of the beam diameter in this evaporation source depends on various parameters such as device geometry, magnetic field intensity, electric power, etc. Therefore, in this research, the effect of those parameters was investigated by conducting experiments and using finite element and modeling software. The simulation results revealed that the effect of the effective parameters on the beam diameter can be predicted to a good extent, so that the diameter of the electron beam decreases by changing the geometrical shape, size and displacement of the output beam components. Then, the new electron gun, compared to the existing prototype, is optimized by applying these changes in the construction of the device and conducting experiments, and its beam diameter is reduced by 40% to be more focused.

One popular method to produce 2D materials is the physical method of liquid phase exfoliation (LPE) utilizing ultrasound technique. In this research, our aim is to obtain the optimum conditions for the exfoliation of 2D materials of graphene from graphite utilizing LPE by simulation of ultrasonic waves irradiation and the pressure difference in the solution using COMSOL physics interactive. These simulations are carried on for the probe of 14 mm in diameter and 22 kHz in frequency, and then for the probe of 22 mm and 40 mm in diameter and 20 kHz frequency to obtain the maximum acoustic pressure difference in the solution. Then the probe, which the simulation shows produces the maximum acoustic pressure difference is used for the experimental investigation of the volume and the density of the graphite solution, which is irradiated by ultrasound for graphene, produced. The numerical simulations give an expectation to have more graphene exfoliation when the pressure difference in solution sonication is more. This expectation is verified by the experimentation. The experimental results which are analyzed using UV-visible spectroscopy, FESEM, TEM, and Raman spectrum show the probes with 14 mm and 22 mm produce less flakes which are in smaller size compared to the probe with diameter 40 mm which few-layer and even bilayer graphene with larger size are observed. Also we observed the density and the volume of the solution has importance in the layer number of the flakes production.

In a polywell reactor, it is critical to have a stable and energetic virtual cathode that is necessary to accelerate ions and create fusion interactions. Increasing the confinement time of virtual cathode electrons is of critical importance in the performance of polywell reactors. In this paper, COMSOL Multiphysics software was used to perform a three-dimensional numerical simulation in order to investigate the impacts of effective variables of a polywell on the virtual cathode. The findings indicated that the confinement time depends on the distance between the coils, coil radius, coil current, and the kinetic energy of the injected electrons. In addition, by using the simulation results, the dependence of the mentioned parameters on the confinement time is obtained, and then a mathematical model was developed.

In this paper, for the first time, improved lasing performance of a red AlGaInP laser diode is demonstrated by introducing a new extreme triple asymmetric waveguide structure. In the new proposed waveguide structure, at the first step, n-waveguide and n- cladding layer thicknesses are increased, and then a triple asymmetry is introduced on the design of the n-type and p-type cladding and waveguide layers inside the red laser diode structure. The conventional symmetric and the new extreme triple asymmetric laser structures performances are theoretically investigated using simulation software PICS3D. 3D simulations of carrier transport, optical waveguiding and self-heating are combined self-consistently in the software. Numerical results show that the new proposed structure performance is significantly improved in comparison to the conventional symmetric structure.  The reasons of improvements are discussed in this investigation. The simulation results show that the use of the new structure reduces the overlap of the optical mode with of high doping regions. On the other hand, by reducing the electron leakage current, an increase in the stimulated recombination rate occurs, which leads to a decrease in the threshold current and an increase in the output power. By reducing the series resistance and increasing the thermal stability of the new proposed structure, the optimality of this structure is confirmed.

Muon particles are produced by the interaction of cosmic rays with molecules in the atmosphere and are decayed to an electron and two neutrinos with a lifetime of 2.2 µs. These electrons move in the water environment faster than the speed of light in the same environment. Therefore, the electrons emit radiation in the blue and violet light range which is known as Cherenkov radiation. In this research, using the Geant4 simulation code, a simple water Cherenkov detector was simulated to study the Cherenkov radiation of electrons caused by muon decay. Using the energy spectrum of optical photons, the detection efficiency of the water Cherenkov detector was calculated 0.067. Also, the mean lifetime and maximum energy of the electrons produced by the muon decay were measured 2.197±0.014 µs and Emax=52.6 MeV, respectively.

In this study, the 199Au nanoparticles production parameters have been investigated by a two-part study.The first part is about the indirect method for production of non-carrier-added (NCA) 199Au radionuclide which was investigated both theoretically and experimentally. We applied MCNPX-2.6 code, TALYS-1.9, and ALICE code, aiming to simulate the reactor core of Tehran Research Reactor (TRR) and determining the activity of 199Au by MCNPX code using cross-sections calculated by TALYS-1.9 and specifying the production yield of 199Au. Also, the excitation function of 199Au was calculated via  reaction by TALYS-1.9 and ALICE/ASH-0.1 codes. As the corresponding experimental approach, we worked on the reactor production of 199Au by utilizing  thermal neutron flux through irradiation of natural Pt target for a specified irradiation time of 21 hours and 10 minutes in TRR. Regarding our facilities for evaluating the production yield, two samples of 11 mg and 15.5 mg natural Pt targets were bombarded in TRR. Because the natural Pt target, consists of five different stable isotopes (192Pt, 194Pt, 195mPt, 196Pt, 198Pt), some radionuclides as impurities will be produced during the reactor bombardment. So, using an enriched Pt target will increase the production yield together with a reduction of the impurity production. To separate 199Au radionuclide from the impurities mentioned above, and also to calculate both the chemical yield and the radionuclide purity of 199Au, two chemical separation techniques were applied. In the first technique, 199Au radionuclide was separated from impurities by employing liquid-liquid extraction (LLX) using ethyl acetate. As a result of this separation, the chemical yield of 199Au radionuclide was more than 99%. In the second technique, 199Au was separated by employing LLX using liquid cation exchanger, Di-(2-Ethylhexyl) phosphoric acid (HDEHP). By applying this technique, the chemical yield of 199Au radionuclide was more than 80% consequently. We calculated the theoretical findings and compared the results with the related experimental values.In the second part of the present study, the synthesis of radioactive 199Au nanoparticles (199AuNPs) have been investigated by the Turkevich method with the aim of produce citrate-gold nanoparticles with different sizes of approximately 50 nm. Possible uses and applications of 199Au nanoparticles in medicine are also discussed.

In this study, calculations related to the mass attenuation coefficient (µ/ρ) of Polyethylene/Bismuth Oxide composite (HDPE-Bi2O3) for different weight percentages of Bi2O3 in the polymer matrix, namely 0 wt%, 1 wt%, 2 wt%, 3 wt%, 5 wt% and 8 wt% for photons with 59 keV energy that can be used in dental radiography centers were simulated using the MCNP code and results were compared with XCOM data. The simulation results of the mass attenuation coefficient of the composite in different weight fractions via the methods of MCNP and XCOM at 59 keV showed a good agreement with each other. The results of this study showed that the Polyethylene/Bismuth Oxide composite material in optimal weight fraction and thickness can be used as a radiation shield in dental radiography centers.

Patient dosimetry plays the essential role in nuclear medicine performed with various method in clinical and research approaches. There are many methods for internal dosimetry which Monte Carlo code with high accuracy has the crucial place compare to others. The principle reason that Monte Carlo couldn’t performed as the clinical method is the high computation time. This method could be use in the complex geometry such as patient but before the implementation of the code, accreditation should be done. This paper aim to present the method of validation the Gate Monte Carlo codes in PET nuclear medicine. The researches were carried out with experimental tests by head and TLD dosimeters and the results were compared with GATE outputs at the same geometry. In the second steps, ICRP110 phantom in two state of lunge to lunge as a source to target organ and liver to lung considered the MIRD internal dosimetry method had been simulated. The S factor were the results of the simulation codes compared with MCNPX Monte Carlo results in the same conditions. The result has shown the accordance between the simulation and experimental data with high accuracy and highlights the role of Monte Carlo in complex geometry as the high accurate and validate methods.

Multipacting which occurs due to high amplification in secondary electrons, is a typical phenomenon in the radiofrequency structures. The Coulomb force between the secondary electrons induces space charge and consequently saturates the multipacting phenomenon. A realistic study of this phenomenon requires considering the effect of space charge. Simulation of the space charge effect by CST PIC STUDIO software is not simply possible and pose some challenges for users. In this paper, it is described how to consider space charge in a single-side multipacting simulation for a simple model. The effect of space charge on the simulation results has been investigated and the threshold of the the radio frequency field amplitude for multipacting occurrence has been obtained.

In this paper the heating effects was investigated with SAMI2 model. An external Gaussian heating source was considered in electron temperature equation that models the radio frequency heating. The effects of the heating were investigated as a function of the heating period, intensity of the heating source, height of the heating center and different latitude of the heating in Iran coordinates.  Results of the simulations show that height of the heating and intensity of the source have main role in the distribution function of the electron density and temperature. This distribution in heating zone and conjugate point was shown. In early time of heating, by increasing the height, the electron temperature was increased dramatically. At low intensity of the heating source, the electron temperature wasn’t increased. However, the electron temperature was increased in heating zone after 30 minutes. Also, the heating distributes the electron density counter which represents the reduction of the electron density and the formation of the duct in heating zone and the growth of the electron density at conjugate point. The results show that at low latitude, electron temperature at heating zone and conjugate point was increased more.

In this research, atom-cavity entanglement in closed Jaynes – Cumming model has been used with the assumption of large detuning between atom and cavity, to simulate the state transfer from atom to cavity radiation. A two-level atom which is prepared in a half-half superposition between the ground and excited states, has been exposed to initially coherent radiation field which is far from resonance with the atom. Mixture of each subsystem, linear entropy, entanglement, Von Neumann entropy and Schmidt decomposition of composite system as a function of time, has been determined analytically, for the first time. Assuming large frequency differences between atom and radiation, the simulation is shown no energy is transferred between atom and radiation due to large detuning, even though atom-radiation entanglement took place. Also, it has been shown that a particular measurement on the atom in this composite entangled system, can project the composite system into a separable (non-entangled) state so that the radiation state is changed into a superposition of the coherent state which is called the cat state. The conditions required to transfer radiation into odd and even cat states have been particularly investigated.

In this paper, the variations of particles distribution function (DF) in a one-dimensional collisionless plasma expansion are studied. It is shown that, for the self-similar cases the initial Maxwellian distribution function of ions gradually converse to a δ-like one. So, the dynamic of the ions could be considered with fluid equations. On the other hand, for the effects of charge separation that occurs assuming the expansion of finite plasma, the process of plasma expansion imposes variations on electrons DF which causes it to change from Maxwellian to a non-Maxwellian one. In order to investigate the electrons DF at each moment, a particle simulation is used. In this simulation, the electrons dynamic is determined by Vlasov equation. Ions dynamic is given by fluids equations. Finally, it is indicated that, the higher energy tails of electrons DF in the main body of plasma are descended due to the motion of high energy electrons into vacuum and the electrons DF transforms to a super-Maxwellian DF. In the opposite side, at ion front zone which is the place of high energy electrons presence, electrons DF transform from Maxwellian to Lorentzian case with the high energy tails

One of the driving factors for creating axial flow inside the gas centrifuge rotor to increase the separation performance is the scoop. Due to the exposure of the scoop to the high Mach gas flow, the flow will be shocked, and strong gradients will occur in the flow.  In this research, the gas flow around the scoop in a two-dimensional state (r-θ) is simulated by the Direct Simulation Monte Carlo method (DSMC) using the dsmcFoam solver at different distances of the scoop from the rotor wall. The results show that increasing the distance of the scoop from the rotor wall and decreasing the contact angle of the gas flow with the scoop reduces the maximum temperature and drag force. For instance, increasing the distance of the scoop from the wall by 31% (from 8 to 10.5 mm) in 3800 Pa wall pressure and 85° contact angle, causing a maximum temperature decrease of 1.3% (from 596 to 588 K) and also the drag force is reduced by 49.4% (2412 to 1221 dyn). Furthermore, reducing the angle of the gas flow with the scoop by 11.8% (from 85 ° to 75 °) in 3800 Pa wall pressure and at the distance of the scoop from the wall equal to 10.5 mm causes a maximum temperature decrease of 6.8% (from 588 To 548 K) and the drag force is reduced by 50.3% (1552 to 771 dyn).