JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY
Year:2021 | Volume:42 | Issue:2 (96)|Papers Count:15

A semi-classical optimization model is introduced for controlling the high-order harmonic generation process and extending the cutoff frequency. This method is capable of defining the driving laser shape interact with the F2 molecule for maximizing the cutoff frequency properly. This optimization procedure is evaluated by examining the high harmonic spectrum from the F2 molecule irradiated by a two-color laser field. High harmonic spectrum is done using time-dependent density functional theory in a threedimensional space. The results showed that adding two driving laser pulses with optimization could enhance the cutoff frequency by 96% compared to two driving laser pulses without optimization. In addition, this model for the F2 molecule is capable of reducing the output attosecond pulse duration from 200 as not optimized two-color laser to 135 as the optimized two-color laser.

In the present work, the performance of a square cascade in the separation phase of tellurium stable isotopes is studied. In this cascade, the selection of an appropriate feed stage, the first stage cut, and the cut of the cascade are the effective parameters. The results showed that in the various separation factors, selection of the middle feed stage leads to appropriate results. Also, if the cut of the first stage is selected in such a way that the cuts of stripping section are obtained the same, it is one of the cut-offs for which the two grouping parameters of components will have the highest possible value. Based on the selection of this cut, one of the possible strategies available through using the code-named SQCASSIM for the separation of tellurium stable isotopes to the enrichment of more than 90% is presented.

Due to the importance of Teflon in the military industries, especially the missile and aerospace industries, the study of the effect of different nuclear radiations on the physical properties of this polymer can greatly assist the fabrication and engineering process of the components used in its manufacture. In this study, Teflon tape was cut into six bands, then five bands were irradiated with different absorbed doses of gamma radiation up to 12 kGy. Moreover, the tensile test were obtained from Teflon samples to evaluate the mechanical properties, and the FTIR spectra to investigate the changes in the structural properties. Through the structural studies, variations such as the formation of double bond in the structure of irradiated Teflon strips were observed. Also, the reduction of the stress and the strain values at the final strength and rupture point were observed by studying the mechanical parameters of the Teflon strips. It was concluded that in the irradiated Teflon strip structure, double bonds are formed which are a sign of major chain failure. Furthermore, no improvement in the mechanical properties was observed.

In the present study, by using one dimensional PIC simulation, we investigate the radiation reaction (RR) effects on the plasma behaviors and self-consistent laser evolutions during the interaction of ultra-high intensity lasers (I~1022-1023 W/cm2) with near-critical plasmas (one-tenth to few times of the critical density). The results show that RR force has significant effects on the induced plasma disturbance and self-consistent laser evolutions. Generally, at higher intensities (~1023 W/cm2), introducing the RR effects leads to enhanced delivered electromagnetic energy to the plasma. This energy is either used to increase the mechanical energy of the plasma disturbance (increasing the effective absorption) or compensation of the radiation energy loss by ultra-violate photon emissions. At lower intensities (~1022 W/cm2), RR phenomenon mostly acts as a damping friction force, and reduces the effective absorption and the plasma wave amplitude. Though the friction effect of the RR force is conceptually well known, the observed enhanced absorption at higher intensities is a complex and anomalous nonlinear phenomenon. In addition, the presence of RR force introduces structural differences in the plasma disturbance and whence the absorption saturation. Here, along with reporting these phenomena as well as comparisons between the classical and quantum frameworks, their possible descriptions have been presented.

Identifying and measuring the radioactivity of airborne particles are necessary and very important to recognizing and estimating the effect of radioactive contamination on human health and the environment. Gamma-ray spectromety is one of the most useful methods for quantitative and qualitative analysis of samples, like air filters. The first and necessary step in performing sample analysis by Gamma-ray spectrometer is to calibrate this equipment which requires appropriate standard sources. The purpose of this research is to design and manufacture a suitable standard source considering filter geometry and its quality control and validation. For this purpose, a circular HEPA air filter with a diameter of 60 mm was used. Gamma-ray spectrometry system (HPGe) was calibrated by mentioned standard source. The results of counting and quality control of the manufactured source showed the accuracy of source manufacturing method. The validation of manufacturing method by Spike method showed an acceptable error of 8%.

Because of many special benefits of the Small Modular Reactors (SMRs) and the Accelerator Driven Subcritical Reactors (ADSRs), they are subject of a large number of studies all over the world. In the present work, the ADS photoneutron target for Holos reactor was designed and optimized by using MCNPX2. 6 code. The Continuous Slowing Down Approximation (CSDA) ranges of passing electrons through tantalum, tungsten, mercury, lead and lead-bismuth were investigated. The production and leakage rates for neutrons and photons, and therefore, the deposited heat from neutrons and photons were calculated considering the electron beam bombardment of tantalum, tungsten, mercury, lead and leadbismuth targets at beam energies of 100– 1000 MeV. Other factors such as the optimization of photoneutron target dimensions for 20 and 200 MeV electron beams, and choosing of the optimal energy of incident electrons for the optimized photoneutron target were examined.

In the present work, a dynamic model of plasma current and its relation with the currents of active coils is derived using the Hamilton-Lagrange and energy functions. Model parameters of the plasma current are calculated using the analytical approach and the parameter estimation methods. The parameter estimation is performed based on the gray-box model. The experimental data of three shots in the presence of plasma in Damavand Tokamak have been used to estimate the parameters of the model. The results of plasma current modeling show a dynamic model with variable parameters as a function of plasma conditions and plasma position. In the present work, based on the obtained dynamical model, a robust PI controller has been designed to control the plasma current using the currents of the central solenoid and equilibrium coil. The simulation results using real experimental data indicate the acceptable performance of the designed control system.

Laser irradiation of polymers leads to the change of structural and optical properties. Because of its favorable features like cheapness and biocompatibility, poly (methyl methacrylate) (PMMA) is one of those polymers that is in widespread use in different areas such as manufacturing medial microfluidic devices. The aim of the present study is to investigate the effects of the pulse number and the abovethreshold fluences of the CO2 laser in the creation of microstructures on the surface of PMMA polymer and variation of its optical properties, like absorption coefficient, refractive index, and bandgap energy. The obtained results indicate the formation of microstructures on the PMMA surface at the abovethreshold fluences of the CO2 laser. At a fixed fluence, the density and width of the microstructures increase and decrease by increasing the number of incident pulses, respectively. By increasing the fluence at a fixed number of incident pulses the same trend forms in the microstructures. In the range of investigated fluences in this study, between 10-50 J/cm2, the width of the microstructures is measured to be between 10-15 micrometers. Consistent with previous experimental results, the results of this study indicate the enhancement of absorption coefficient, bandgap, and refractive index of the PMMA polymer after interaction with the CO2 laser.

The study of the process of absorption and evaporation of fluids in porous media is of particular importance in sciences such as geology, civil engineering, environment, etc. Neutron radiography is one of the most precise methods for investigation of the mentioned processes. Due to the high cross-section of the interaction of thermal neutrons with hydrogen, precise investigation of absorption and evaporation of fluids containing hydrogen, such as water, oil, etc., is possible. In the present work, using the real-time neutron radiography technique, the vaporization of water from a porous building sample at 10 ° C in the laboratory was investigated. For this purpose, a building brick was immersed into water for 24 hours, and then was placed in front of the neutron beam. During 145 minutes of reactor operation, 30 images were recorded with a 5 minutes interval from the wet sample. The obtained images showed that using the utilized technique, the distribution variations and volumetric water content inside the sample are well visible. Also, the results indicated that the volumetric water content in the sample was evaporated with a rate of 3. 94×10-4 percent per seconds in the laboratory environment.

Laser produced plasma can be used as the sources of soft X-ray laser. The ability to control the laser quality and its gain coefficient by controlling laser and plasma’ s parameters is one of the advantages of this method. In this study, a pump pulse assistant along with a pre-pulse is irradiated on a geranium target as the plasma active medium, thenthe gain of soft X-ray laser at wavelength 19. 6 nm is calculated. In order to analyze the effect of laser parameters such as intensity, pulse length, and time delay between two pulses, MED103 hydrodynamic code has been used. The simulation results show that there is optimal pulse duration for the pre-pulse as well as the main pump pulse to achieve the maximum gain of soft Xray laser. In addition, according to the results, by increasing the pre-pulse intensity the amount of soft Xray laser gain initially increases and then decreases, while by enhancing the main pulse intensity, it keeps increasing. Also, the optimal spatiotemporal regions of the soft X-ray laser gain for different time delays of two pulses are given.

Due to the limited uranium reserves and advantages of thorium fuels over uranium fuels, the development of the thorium fuel cycle in various countries including Iran, has been considered significantly. One type of thorium fuels used in nuclear reactors is a mixture of uranium dioxide and thorium. The type of powder synthesis method is a key point in improving the efficiency of this fuel in the reactor. The main objective of the present study was to achieve mixed nanoparticles of 30-70% (Th-U)O2. The effect of four parameters including concentration, time, initial percentage of uranium-thorium nitrate in solution, and temperature was studied using Taguchi's experimental design. The synthesized nanoparticles were characterized by XRD, BET, EDS, and SEM analyses. The results showed that at the best conditions, the nanoparticles were synthesized with a weight percentage of 32. 28 and 67. 72%, a particle size of 13. 25 nm, high purity, and high surface area. Also, the results showed that the supercritical hydrothermal method has performed well for mixed nanoparticles of 30-70% (Th-U)O2 production.

In the present study, the possibility of uranium recovery from aqueous solutions was investigated using electrodialysis process. Also, the effect of separation time, electrical potential difference, flow rate, acidity, uranium concentration, and concentration of electrodes wash solution were studied. The results showed that the electrodialysis process remained stable in less than 20 minutes. As the electrical potential difference rises from 5 to 20 V, the separation of uranium increased and then remained constant due to the hydrolysis phenomenon. Due to less resistance, the membrane module performance of the single-cell was more appropriate than the multi-cell module. In addition, the uranium separation was reduced by increasing the flow rate and the feed concentration, according to the reduction of residence time and increasing the concentration polarization phenomenon. Anothert result was that the increase of feed solution acidity reduced the uranium separation and increased the electric current, which can be justified by the competition between acid ions and uranium. By increasing the concentration of sodium nitrate in the electrodes wash solution from 0. 01 to 0. 25 M, the percentage of uranium separation increased. The results of this study showed that the recovery of the uranium from aqueous solutions using electrodialysis process is possible.

Physical systems are mostly modeled by certain differential equations. However, in most cases random effects are omitted and therefore, the solutions are not in agreement with the experimental results. In the present work, we have investigated the effect of white noise perturbation on two physical models. At first, we have reviewed the random variables and processes and then, we have solved the Langevin equation, which is a general form of a random equation with a random white noise perturbation. We have also proposed a stochastic model for both the electric current and radiation of radioactive materials. This is done by considering the white noise perturbation sentence in the corresponding ordinary differential equations. By solving these random equations, we have obtained the mean value function, the variance function, and the random process function, as well. Finally, the results have been simulated and the corresponding diagrams presented. In order to simulate the desired random movement, the Monte Carlo method in Microsoft Excel environment was used.

The Scandium-47 shows undertaking capability in therapeutic radionuclide, particularly in the singlephoton emission computed tomography (SPECT) technique. In this study, for the production of the 47Sc, the proton interaction on natural titanium was investigated by the Karaj cyclotron. At first, the excitation functions for the production of 47Sc and accompanying impurities via proton bombardment of titanium targets were evaluated by three nuclear codes, TALYS-1. 9, ALICE/ASH, and EMPIRE-3. 2. 2. The target thickness for the best range of suggested energy estimated through the stopping power using the SRIM-2013 code. The theoretical yields for each reaction were calculated using Simpson's integral. The natTi foil was irradiated by a 29. 5 MeV incident proton beam in the Karaj Cyclotron. The total current irradiated on the target was 5 μ A· h at the end of the bombardment. The liquid-liquid extraction (LLX) method was employed for the separation of radiochemical impurities. Quality control was performed by γ-ray spectrometry. The separation yield of scandium-47 was 95%. The results showed good agreement with simulated and published experimental data.

The availability of current AC electrical power is essential for the safe operation and accident recovery of commercial nuclear power plants. Loss of offsite power (LOOP) considers as one of the significant post-Fukushima accidents. When the onsite diesel generators are not recovered in the power plant, the accident encounters with station blackout (SBO) situation. In this study, the emergency AC power recovery is investigated during SB-LOCA along with LOOP accident for 25 mm, 50 mm, and 100 mm breaks with RELAP5 thermal-hydronic. Likewise, in evaluating the emergency power recovery scenario, the power plant's recovery in the first and second hours has been investigated. The results showed that in the first hour of emergency power recovery, the reactor is not reached the core damage threshold in all three breaks. Meanwhile, in the second hour of emergency power recovery for 25 mm and 50 mm, the reactor core reaches to core damage threshold before the emergency diesel generators are activated. Therefore, the results show that in SB-LOCAs with a lack of emergency power recovery, there is a chance to recover emergency power and safety systems at least until the first hour.