مجله علوم و فنون هسته ای
سال چهل و سوم شماره 3 (پیاپی 101، پاییز 1401)

Over the past few decades, computed tomography (CT) imaging has been merged as one of the leading cross-sectional imaging techniques in a wide range of clinical applications in diagnostic radiology, oncology, and multimodal molecular imaging. Despite the recognized value of this imaging modality, the quality and accuracy of CT images can be compromised by a number of implants. The presence of metal objects such as dental fillings, hip or knee prostheses, heart pacemakers, war fragments, and spinal cages can cause severe image artifacts. These types of artifacts appear as black and white streaks in the CT images, obscuring the structures and tissues around the metal implant which decreases the diagnostic values of the images. Metal artifacts also affect the accuracy of radiation therapy treatment planning, which relies on X-ray images to determine electron density and estimate the relative stopping power of particles. In this regard, different algorithms of the Metal Artifact Reduction (MAR) have been proposed over the decades to address this issue. In this study, five commonly used MAR algorithms in clinical practice have been evaluated using simulated and clinical datasets. These algorithms include linear interpolation (LI_MAR) of the degraded data in the sinogram space, reduction of metal artifacts by normalization method (NMAR), metal deletion technique (MDT), Orthopedic metal artifact reduction (OMAR), and a method based on iteration algorithms (MAP). Clinical CT images in different anatomical regions of the body, with different dimensions and types of metal implants, have been studied to evaluate the performance of the MAR algorithms. In order to quantitatively evaluate the quality of CT images corrected by the different MAR algorithms, the Normalized Root Mean Square Error (NRMSE) metric was employed. The quantitative analysis demonstrated the overall superior performance of the NMAR algorithm in effective metal artifact reduction compared to the other algorithms. The NMAR method exhibited relatively less signal distortion and reasonable processing time which make it a dependable solution in clinical practice.

In this study, we used the Monte Carlo-based software, GATE, to model the spot scanning proton therapy system (SIEMENS IONTRIS spot scanning dedicated nozzle) installed at the Shanghai Proton and Heavy Ion facility. Within the nozzle, apart from entrance and exit windows and the two ion chambers, the beam traverses through the vacuum, allowing for a convergent beam downstream of the nozzle exit. We model the angular, spatial, and energy distributions of the beam phase space at the nozzle exit with single Gaussians, controlled by eight energy-dependent parameters. The parameters were determined from measured profiles and depth dose distributions. Verification of the beam model was done by comparing measured data and GATE acquired relative dose distributions, using plan specific log files from the machine to specify beam spot positions and energy. The MC simulations showed good agreement with measurements for the depth-dose curve and SOBP plans. The absolute comparison of the absorbed dose difference between the MC and the measurement was ±1%. This work describes a method for adapting a MC simulation model for a spot scanning proton delivery system. The excellent agreement between the measurements and simulations shows that the MC modeling in this work is a precise and reputable method.

In this work, the surfaces of spherical mesoporous silica were modified with potassium copper hexacyanoferrate ([KCu(Fe(CN)6)]), then employed as a new ion exchanger nanocomposite to adsorb cesium ion from an aqueous solution. The materials have been characterized by Field EmissionScanning Electron Microscopy (FESEM), X-ray diffraction (XRD), N2 adsorption-desorption isotherms (BET), and FTIR spectroscopy. The effect of contact time, pH, and initial concentration of the solution on adsorption efficiency were studied. Langmuir, Freundlich, and Tempkin's isotherm models analyzed the equilibrium concentration data. The data was in good agreement with the Langmuir model showing cesium adsorption process was a monolayer. The pseudo-second-order model was adequate to describe cesium uptake kinetic behavior, and the maximum equilibrium adsorption capacity for the nanocomposite was 46/4 (mg/g).

Considering the importance of nuclear asymmetry matter in heavy-ion interactions, in the present study, we have divided the interacting systems into three different groups, including isotopic, isobaric, and isotonic systems, and examined the characteristics of the fusion barrier for each group separately using 27 different versions of proximity formalism. Our results show that for calculating and predicting the fusion barrier characteristics in heavy ions interactions, it is more proper to use different versions of proximity formalism, instead of a single performance, based on the isospin degrees of freedom.

This paper aims to design a suitable irradiation box of topaz stones and improve the neutronic parameters by maintaining the necessary conditions for their cooling in Tehran Research Reactor (TRR). In this way, by defining an appropriate neutron filter and simulating the irradiation box in the TRR core with MCNPX2.7 code, the neutronic parameters of the core are calculated, and the best configuration is selected. Then, various components of the irradiation channel are simulated using the Solidworks software, and thermal calculations are performed using the Flow Simulation plug-in. The results showed that although the presence of water in the irradiation channel and topaz box results in good cooling for topaz stones, the slowdown of fast neutrons causes intense activation of the stones. However, by using a closed-loop independent of the reactor pool water and a gaseous fluid such as air, the thermal neutron flux and consequently the activity of the stones is reduced. Moreover, the results demonstrated that, in this case, acceptable conditions could be provided for long-term and safe irradiation of stones by selecting the appropriate fluid velocity and adjusting the core power.

In this article, an optical system for pumping the active medium of solid-state lasers with light-emitting diodes (LEDs) is introduced to upgrade the master oscillator of the laser fusion facility. The optical system is based on the guiding of optical rays from light-emitting diode sources to laser rods by means of total reflecting surfaces. Three different configurations with four, five, and six segments have been designed and their geometry is optimized with 3D random ray-tracing method to obtain the best performance. The pump systems have been fabricated and successfully applied to pump a 3 mm diameter laser rod with 10 watts white spectrum LEDs. Using five segments configuration and 4 Joules electrical energy delivered to 35 LEDs, the laser oscillator produced laser spikes with multi-mode Ince-Gaussian transverse beam structure and more than 700 micro-joules laser energy at a 1 Hz repetition rate. Moreover, the Q-switched pulses with an average energy of about 35 micro-joules and 230 ns pulse-width have been generated with the optimized optical pump system. More improvement to the LED-pump system is possible, which can be led to an efficient multi-mJ laser beam.

One of the crucial parameters in designing the Q model cascade for the multi-component systems is the M* parameter. In this research, a code called MOTACAS has been developed to design a Q cascade, using the optimal value of the M* parameter. In this regard, the enrichment of the 8th isotope of tellurium at the heavy stream to 0.40, 0.7, 0.9, and 0.99, and the enrichment of the 4th isotope to 0.1, 0.3, 0.4, and 0.5 have been investigated. Also, in order to evaluate the effect of the separation factor on M*, optimal Q cascades for the enrichment of the 8th and the 4th isotopes with separation factors of 1.05 and 1.1 have been designed and compared with each other. The results show that the acceptable range of the M* decreases with increasing the desired isotope concentration. The optimal value of the M* does not change with reducing the separation factor. The relative inter-stage flow rate remains constant despite increasing the total inter-stage flow rate. Moreover, the required number of separation stages to reach the end component to a high concentration increased, but the enrichment of the middle component in the one cascade is limited despite increasing the stages.

Zr-1%Nb alloy is the most common alloy used as nuclear fuel cladding in Russian reactors. In producing a nuclear fuel cladding, the cold rolling (pilger) and the final straightening lead to the creation of residual stresses and a change in the distribution of these stresses within the fuel cladding. The residual stresses are known to be effective in increasing the hydride fraction in nuclear fuel pods formed under working conditions by hydrogen adsorption of water and have destructive effects. In this study, the residual stresses created in different stages of fuel cladding fabrication, including samples before annealing, post-annealing, and straightening, were measured using X-ray diffraction and splitting. In addition, the amount of hydride fraction in different samples was evaluated. The effect of annealing on the orientation of hydrides was performed in annealing at 500, 540, and 580 °C for 4 hours.

In the design of tapered cascades, due to hydrodynamic problems, not every cascade can be operated. This paper describes the method of designing and optimizing a tapered cascade for the separation of stable multi-component mixtures by considering the operational parameters of the gas centrifuge machine. In this method, the hydraulic specifications and separation of the centrifuge machine are determined in the first stage. Then, using this information and optimization algorithms, the optimal cascade is designed with the least number of centrifugal machines. This paper uses the grey wolf optimization algorithm to find the optimal cascade. The cascade operation is checked using the hydraulic parameters of the gas centrifuge,. The operational limitation of the cascade is added hydraulically to the fitness function in optimization. To determine the hydraulic characteristics of the gas centrifuge, a transient simulation of the gas centrifuge hydrodynamic is presented and the relationship between product and waste pressure lines, feed flow, and cut is determined. Using the proposed design method, an operational cascade is designed using a TC-12 centrifuge machine to separate the uranium 235 isotope from the reprocessed fuel to a 4% enrichment. And the pressure variation in the cascade is presented.

This paper investigates the stochastic heating of electrons caused by Raman backscatter radiations during the interaction of a laser pulse with helium atoms by means of a parallel particle-in-cell (PIC) code. At different propagation times, the self-consistent laser pulse changes are investigated via the space-time Fourier transform of the transverse vector potential. It is demonstrated that, since ionization has a striking influence on the emission of Raman backscattered radiation, it also plays an important role in the threshold of electron stochastic heating. As demonstrated by the experiments, the Raman backscattered radiations are initiated by a strong initial noise when a laser pulse has a long rise time, 100 fs. Hence, the fundamental condition for the chaos threshold is satisfied sooner by examining ionization effects. In this manner, stochastic heating of the electrons is initiated more rapidly than if the laser pulse were emitted in the preplasma. Accordingly, in concurrence with the idea of chaos, the electrons acquire more energy via the stochastic mechanism in the field-ionized plasma.

Although nuclear energy and radioactive materials have considerably impressed national health and economics, inappropriate use of radioactive materials can pose a significant threat to public health and security. This research aims to enhance defensive capabilities for countering nuclear terrorism by accurate detection and continuous tracking. A vital component of this system is to equip surveillance cameras of a region with a relatively low-cost radiation detector (NaI detectors) for counting gamma rays. Data-fusion of the surveillance camera and radioactive sensor that is linked together helps us detect and localize suspicious sources among other objects. The system can provide data flow (continuous) or a collection of snapshots several times (discontinuous), then a fast and new algorithm detects the suspicious source in these two modes. The promising results represent the integrated system by employing the new algorithm to detect the suspicious source in both data modes. Still, the source can be detected quicker in the continuous mode.

Magnetic hydroxyapatite nanoparticles (Fe3O4/HAP) are prepared in the present work to remove uranyl ions via copercipitation method for the first time. The sorbent was prepared with the weight ratio of magnetic nanoparticles to hydroxyapatite (Fe3O4/HAP) as (1:1), (1:2), (1:3), and (1:5). After finding physical, chemical, and magnetic features, their ability to absorb uranyl ions was examined via UV-Vis method, measuring the absorbance of element complex with arsenazo (III). The effects of parameters such as temperature, pH, contact time, rate of the adsorbent, the concentration of uranyl, and the effects of interference of other ions on the removal of uranyl were analyzed. Also, the experiments showed that the highest rate of uranyl was absorbed by using 0.015 g Fe3O4/HAP (1:5) during 150 min at pH equal to 7. The prepared nanoparticles in 17±2 nm could absorb uranyl in the concentration range of 0.2-100 ppm, eliminating over 96% of uranyl. The absorbing capability of 99.82 mg/g was obtained at 25°C. The results indicate the high potential of the prepared nano-particles in absorbing and eliminating uranyl and show its capability in the waste water containing uranyl.

In this paper, in order to investigate the surface fusion phenomenon in an industrial neutron generator, a solid target with cooling capability was designed and constructed. The first step to achieving this goal is to thoroughly investigate the material and thickness of the layers and substrates suitable for use as solid targets for industrial neutron generators, using SRIM-code simulations. Then, using the simulation results, samples of the solid target were constructed by the sputtering coating method. In addition, due to the importance of the target temperature and its effect on surface fusion, the cooling system using COMSOL multiple physics simulation software, was designed and built. In addition, to insulate the high voltage applied to the target which is in contact with the cooling system, various electrical insulators were studied and suitable insulation was selected, designed, and manufactured. Then, to test the solid targets and their side parts, a suitable vacuum system was designed and constructed. Finally, after designing and constructing all the parts, the system was assembled and set up for final testing. In deuterium filling gas tests, the neutron flux was measured using the LB6411, 3He detector. At around 25 kV voltage and 20 mA current, we were able to detect neutrons with the rate of 6 × 105 n/s, which was a sign of success. This amount of neutron production indicates duplication of the neutron rate produced by the surface fusion phenomenon.

In this research work, we used the Deuteron Induced Gamma-ray Emission (DIGE) method based on 18O(d,pγ)19O (Eγ=1376 keV), and 16O(d,pγ)17O (Eγ= 871 keV) nuclear reactions to determine absolute amounts of the stable isotopes 16O  and 18O in the irradiated H218O sample. This sample had been bombarded as a target by the proton beam of a cyclotron accelerator in order to 18F radioisotope production. The employed thin Ta2O5 target was prepared by anodizing tantalum backing with the sample of irradiated H218O. The main advantage of PIGE is in measuring the simultaneity of the isotopes 16O and 18O only using one experience with a deuteron beam. The method's reliability was checked by determining isotope 18O for a sample with given 18O enrichment. These measurements were conducted using the 1150 keV deuteron beam of the 3 MV Van de Graaff electrostatic accelerator of the Nuclear Science and Technology Research Institute (NSTRI).

Event tree analysis is applied to quantify the core damage frequency (CDF) and assess the risk of nuclear power plants (NPPs) resulting from various postulated initiating events. To calculate this criterion, it is necessary to generate the probable scenarios according to the function of safety systems and the operator's actions. The classical event tree is currently used in PSA analysis. This method does not consider the accident's dynamics and scenarios. It considers only the availability/unavailability of the safety system functions and the operator's actions to calculate the frequency of each scenario. In contrast, the dynamic event tree method applies physical and probabilistic models to generate branches in the event tree, calculate the frequency of each scenario, determine the time profile of core damage, and time variation of physical parameters of the NPP for each scenario. This paper develops the dynamic event tree for the SBO accident at the VVER-1000/V446 NPP using the RELAP5 and RAVEN codes. The results are then compared with the outputs of the classical event tree. The results show that according to the assumptions, 3170 scenarios are evaluated in the dynamic event tree, while only 33 predetermined scenarios are examined in the conventional event tree. The calculated core damage frequencies are 3.61×10-6 (yr-1) and 1.97×10-6 (yr-1) for conventional and dynamic event trees, respectively.

In this study,the values of total excitation energy (TXE) of fission fragments are calculated for neutron fission of Plutonium isotopes using two methods. At first, the calculated TXE values using two methods are compared for neutron fission of plutonium 239. Then, the calculated TXE values using the second method are improved based on the results of the first method. TXE distribution of plutonium 241 and 242, which have the measured fission fragment total kinetic energy, are calculated using two methods and according to the method modification. Also, the TXE distributions for neutron fission of other plutonium isotopes are predicted. The values of total excitation energy of fission fragments for plutonium isotopes are between 15 MeV and 35 MeV. The TXE values have a sudden increase in the symmetric region.

This work investigates the effects of different operational parameters on the pulse shape of a homemade high repetition rate (1 kHz) pulsed CO2 laser. Various parameters such as the ratio of N2 and He in the laser gas mixture and the reflectivity of the laser front mirror have changed. Then, the energy and shape of the laser pulses were recorded and analyzed. It showed that by varying the ratios of N2 and He in the laser gas mixture, the time duration of the spike and tail parts of the laser pulses can be changed in 95-140 ns and 1.5-3.5 µs range, respectively. In addition, we found that when the reflectivity of the cavity front mirror increases from 50% up to 80%, the spike duration increases from 50 ns up to 90 ns, and the tail duration decreases from 4.8 µs to 2.5 µs.

This paper investigated the temporal behavior of the backward Stokes pulse from a stimulated Brillouin scattering phase conjugate mirror (SBS_PCM) in a pure acetone medium. Changes in the reflected energy of the phase-conjugate mirror and the temporal width of the Stokes pulse due to changes in the input energy flux to the cell and changes in the interaction length were studied for the single-cell structure. For this purpose, to achieve the optimal optical arrangement for maximum efficiency and minimum pulse width in full width half maximum, the cell length and the geometric structure of the phase conjugate mirror have been changed. Variations of the energy and the reflected Stokes pulse width of the phase conjugate mirror were compared for the considered cases. The results show that the reflected energy of the phase conjugate mirror can be optimized by changing the interaction geometry. By increasing the intensity of the input beam at constant energy and changing the interaction length, the minimum reflected pulse width was achieved in terms of input energy.

Nowadays, the use of nanoparticles has made many developments to enhance the effectiveness of radiotherapy. Many parameters such as size, concentration, type, and intracellular position of nanoparticles, as well as type and energy of the radiation source, affect the sensitivity. In this study, the effect of the presence of gadolinium in the cell has been investigated, and the role of these physical parameters has been evaluated in the dose-enhancement factor (DEF). Using Geant4 software, different distributions of gadolinium nanoparticles (GdNP) and gadolinium atoms were simulated inside a cell. The sources of low energy (25 keV- 80 keV) and high energy from linear electron accelerator (Eave =2 MeV) were irradiated to a single cell, and the dose was obtained in its membrane cytoplasm, and the nucleus was calculated. Then, the effect of its size and X-ray source energy on the DEF value was investigated by simulating a nanoparticle. At the cellular scale, a rapid increase in DEF occurred after the Gd K-edge. The lowest DEF is in the core. The maximum DEF belongs to the distribution of Gd atoms in the cytoplasm and the distribution of Gd nanoparticles in the membrane with the values of 1.20 and 1.17 at 52 keV, respectively. At 2 MeV, the DEF in all distributions is close to 1. At the nanoscale, it was also found that the highest DEF was related to nanoparticles with a radius of 50 nm. Also, the DEF value increases sharply after the Gd K-edge, but at 2 MeV, the DEF value approaches 1.

Calculating and measuring the gamma dose of nuclear reactors is important in terms of safety and protection and is used for organizations' design and development programs. In order to achieve this goal, experimental measurement with RADOS and SMART-RAD digital dosimeters and calculations based on Monte Carlo code has been used.The three-dimensional geometry of the light water subcritical reactor of Isfahan Reactor Research School was simulated for gamma dosimetry calculation with the MCNPX2.6 code. The effective multiplication factor was estimated prior to dose calculation and revealed to be less than 6% different from the value reported in the reactor technical specifications. Analyses were performed to obtain the sought parameter, gamma dose (µSv/h), following the validation of the reactor simulation code. The F4 and F5, F4 and *F8, and *F8 and F5 tallies differed by less than 5%, 2%, and 4%, respectively. The difference between the measured and calculated values was found to be reasonable and acceptable compared to similar previous studies.