مجله علوم و فنون هسته ای
سال چهل و سوم شماره 1 (پیاپی 99، بهار 1401)

The space environment can cause severe problems for electronic circuits. The plasma, radiation, debris, and no thermal convection are some space environment-specific conditions. Space radiations are the source of several damages, such as total ionizing dose (TID). During a satellite’s mission life, the TID gradually degrades the quality of the electronic components. Designing reliable equipment requires enough information about the mission environment. Some part of this information could be obtained employing dosimetry. There are several dosimeters based on the type and intensity of radiation sources. In the present work, a dosimeter has been introduced that could measure the TID for a satellite in a low earth orbit. This dosimeter uses a RadFET to measure the TID. The simulation results and implemented version of the dosimeter verify the accuracy and quality of the proposed dosimeter. The low power consumption, fast data recording, and thermal stability are some of the features of the proposed dosimeter

Central ignition is one of the main ideas of inertial confinement fusion in which the target is irradiated symmetrically and uniformly by laser beams. The study of target layer design using hydrodynamic codes is very important in improving target performance and fuel gain. Therefore, in the present study, we investigated the optimization of a typical spherical target with a polystyrene ablator by using MULTI-IFE hydrodynamic code. Considering the remarkable physical properties of diamond, it has been used to optimize the ablator layer. This target was irradiated with symmetrical laser beams with 1.7 MJ total pulse energy and peak power of about 600 TW. The results show that the optimal thickness of the diamond is about 18 mm. A diamond ablator increases the absorbed laser energy at the target surface by about 16%. Increasing the absorbed energy leads to an increase of about 4% in the maximum temperature of the ions, and as a result, the fuel burn fraction increases by about 1%. Eventually, fuel gain increases by about 9%.

One of the most effective methods of treating thyroid cancer is iodine therapy. Patients are prescribed orally after thyroidectomy or thyroid tissue resection to control tumor growth and prevent secondary symptoms after iodine surgery. Also, due to the dose of radioactive iodine absorbed by cancer cells in the thyroid gland, it may have many side effects for those around the patient, which in this study in the radiotherapy center of Afshar Clinic in Yazd, using germanium dosimeters TLD-100 is the average absorbed dose of thyroid area on the skin surface after 24 hours to receive 100 to 150 mCi of iodine 131 and the deeply absorbed dose of thyroid at a distance of 7 cm from the skin, which includes the thyroid and surrounding soft tissue 388.933 and 379.155 cGy, respectively. After 48 hours, these values were 350.643 and 344.124 cGy, respectively. Moreover, the measured dose was around the patient. At distances of 1 to 3 m from them during 24 to 48 hours of hospitalization after radiation, iodine intake is on average 30.93 cGy, which is a high risk for those around the patient compared to the set standards. According to the results of studies published so far, age and gender are very effective in the incidence of this disease, and its prevalence is higher in women than men. Therefore, it is suggested that research be conducted on genetic factors and common underlying diseases in each region.

Proton beam therapy (PBT) is a modern radiotherapy technique characterized by superior target coverage compared to conventional modalities. In this work, a comprehensive GATE Monte Carlo model was developed and then validated for a double scattering proton treatment nozzle. To this aim, a double scattering treatment nozzle was modeled in the GATE toolkit. Proton beam flatness and its symmetry, secondary neutron effective dose, and dosimetric performance were characterized. A proton beam flatness of 98.6% was observed downstream of the aperture for a 7×7 cm2 field size. The beam flatness deteriorates at the edge of the treatment field for the single scattering model while it remains approximately constant for the double scattering one. Compared to the single scattering delivery, the second scattering model results in a 1.3 times increase in neutron dose for the nickel as the optimal collimator/aperture material. Furthermore, a flat beam modulation width of 3.50 cm is formed with a distal edge at 7.86 cm in water using the GATE and MCNPX codes. The GATE model agreed with the MCNPX results. The results show that the constructed GATE model results in a fast and accurate simulation of passive scattering PBT.

The laser back writing process (LBW) on the glass and quartz has been studied in the present work. For this purpose, a steel target was irradiated with Q-switched Nd:YAG laser pulses. As a consequence of the laser irradiation, the produced plasma is penetrated onto the glass and quartz substrates. The process was compared for two different samples. The effects of the pulse numbers and the laser fluence on the morphology and the target material penetration on the substrate were investigated. The results show that this process produces microchannels with the controlled dimensions (the depth and width) on the substrate. The presence of the nanoparticles (Fe and Cr ions on quartz and Fe ions on glass) is an important result of this process that can affect the microchannels' function. Irradiation parameters, including the number of pulses, the laser fluence, the pulse repetition rate, and the substrate material, affect the channel quality and the type and rate of the ion penetrated onto the substrates. The width of the channels for the quartz sample is greater than that of the glass sample, and also, more ions are deposited on the quartz substrate than the glass. The EDX and UV-Visible spectroscopies were used for studying the penetration rate and the type of ions present on the substrates. The surface profilometer and scanning electron microscopy were used to investigate the profile and the width of the affected area. X-ray fluorescence spectroscopy (XRF) was used to study the metal target's composition.

Today, problems such as global climate change and its consequences such as floods, droughts, melting glaciers, ocean water level rise are considered globally, and actions should be taken immediately to contain these problems. Many sources pointed to the positive aspects of using organic matter such as biochar to retain soil moisture and plant nutrients, reducing nitrate leaching and greenhouse gas emissions. Biochar is a carbon-rich compound produced by pyrolysis of natural organic matter. In the present study, 0% biochar (B1), 2.5% biochar (B2), 5% biochar (B3), and 7.5% biochar (B4), 2.5% wheat straw (W1), and 5% straw (W2) were added to soil with clay loam texture (S1) and sandy loam soil (S2). This pot experiment was implemented based on a completely randomized design in three replications in the greenhouse using 15N Isotope tracing method. Due to biochar application, Crop yield and nitrogen fertilizer use efficiency increased. This increase was particularly significant in S1B4 treatment (P < 0.01) and reached up to 35%. Straw reduced nitrogen fertilizer utilization in S1W2 and S2W2 treatments by 94% and 87%, respectively

The Zakharov-Kuznetsov-Burgers (ZKB) equation for the Dust Ion Acoustic (DIA) Shock waves in four-component magnetized dusty plasma using standard reductive perturbation technique and hydrodynamics model have been theoretically investigated. Plasma medium is collisionless and contains inertia less Fermi-Dirac distributed electrons and positrons, cold classical ions, and damaging dust grains, which are affected by dust charge variations. By considering an external magnetic field in the desired direction, It can be seen that the specifications of DIA shock waves are significantly affected by the quantum Bohm potential term (H), magnetic field strength (Ωc), dust concentration (d), direction cosines (l), and viscosity of ions (η˳). The present research results can help study the physical mechanism of nonlinear propagation of DIA shock waves in laboratory and space plasmas where quantum electrons and positrons, dust particles, and ions can exist.

Studies on high gradient linear accelerators are among the new areas in the field of accelerators. The most important factor that limits the electric field gradient in linear accelerators is the radio frequency breakdown. Many studies have been conducted on the effect of the material and manufacturing method of cavities on the achievable gradient, which shows that rigid structures fabricated without high-temperature processes achieve a better high gradient performance. Employing the brazing method, as the most common method for construction of cavities, requires the use of high-temperature furnaces, which causes softening of the copper. Therefore, using non-brazing methods to construct high gradient cavities has been considered. Based on the experiences gained in the national electron linear accelerator project at the institute for research in fundamental science (IPM) and the shrinking fit method used to fabricate and assemble its acceleration cavities, the design and construction of high gradient S-band cavities are in progress with international cooperation. Radiofrequency design of cavity with vacuum breakdown consideration and coupler design are discussed. Achieving the appropriate shape and dimensions of the cavity and coupler for maximizing the axial electric field (134 MV/m) with a breakdown rate of less than  at 8 MW input power and S11 parameter -60 dB for the coupler are the results of this article.

According to the safety analyses, GR-LOOP holds the most significant contribution in the Core Damage Frequency of Nuclear Power Plants. Since this, in turn, depends on the GR-LOOP frequency of occurrence, an analytical method is presented to identify and evaluate the post-fault GR-LOOP scenarios. The probabilistic module of the hybrid method develops the post-fault sequences regarding the response of the line distance protection to 3-phase short circuit faults. Then, GR-LOOP consequences and frequency are identified by interpretation of the relevant parameters from the transient stability simulations of the post-fault (3Ph-SC) grid behavior. GR-LOOP frequency is estimated as 5.87E-04, 6.25E-04, and 8.60E-04/ (reactor-year) for three NPPs in New England Test System grid as a case study. To this end, 2482 probabilistic sequences and 408 dynamic post-fault scenarios were evaluated for each NPP. The results indicate that GR-LOOP occurrence depends on the real-time values of grid parameters, including the components specifications, pre-fault load flow quantities, and network configuration. Furthermore, the observed difference amongst the GR-LOOP sequences for differently-located NPPs in the grid questions the uncertainty of using mean generic frequencies. Regarding the inapplicability of the existing grid reliability assessment approaches, the hybrid method is recommended as an alternative for GR-LOOP evaluation. Besides, it can reveal the design weaknesses and prioritize the operational tasks via the competitive benefits of employing PSA techniques. Albeit, more precision needs more modifications in both modeling and calculation details, which, in turn, increases the complexity.

X-rays and neutron radiography images are one of the most effective defects and structure detection methods. The interactions between neutrons and X-rays are different in the material, and therefore, different information can be obtained from the radiographs. Due to neutron and X-rays photon scattering, focal spot size, electronic noises, etc., the images are blurred and their quality is reduced. In this study, while investigating the radiographs of X-rays, and neutrons, the defects and internal structure of objects are investigated. The results show that neutron radiography performs very well in detecting the internal structure of low atomic number materials. X-ray radiography is effective for high atomic numbers as metal. Gaussian convolution is used to enhance the radiography images and reduce blurriness components. The results show that by reducing the background, the blurriness components can be reduced and the defects areas and internal structure of the objects can be better investigated. Specialists evaluated the results in radiography; the results show that the expert’s evaluation approved the image enhancement.

To increase the performance of a gas centrifuge, it is necessary to stabilize an axial flow inside the rotor. For this purpose, computer simulation is an effective method. In the present work, a specific solver (ICDB) was developed in OpenFOAM to simulate the gas flow in the rotor. Creating a solver is important because OpenFOAM is free and open-source software. According to a study carried out by a research group, high-speed airflow is considered on a flat plate to assess the accuracy of this solver. To validate the ICDB, the results are compared with those of Fluent software and other researchers. It is found that the results corresponding to ICDB solver are in good agreement with other effects. Moreover, using the ICDB solver and the fluent software, the uranium hexafluoride gas flow inside the axisymmetric rotor was simulated considering different drives such as the thermal drive (wall and caps) and the mechanical drive (scoop). The obtained results show that the developed solver in OpenFOAM can simulate the uranium hexafluoride gas flow inside the rotor.

Calculation of distribution coefficients is one of the essential provisions in the safety assessment of radioactive waste repository and safe management of radioactive waste. Due to the importance and characteristics of thorium radionuclide in radioactive waste inventory, the distribution coefficient of thorium in the alluvium soil of Anarak Radioactive Waste Repository was determined by the Batch method two parameters of thorium concentration and soil granulation were studied. Also, the Flow-Through method studied the adsorption behavior of thorium has investigated the effect of thorium concentration and soil height. The average value of thorium distribution coefficient in Anarak soil was calculated 110960 L/kg using the Batch method. The study of adsorption behavior by the Flow-Through method demonstrated high uptake of thorium in the soil due to the strong bond created between the ion and the adsorbent. The results showed that the distribution coefficient increases with the decrease of soil particle size. Regarding the effect of concentration on the thorium distribution coefficient, first, an increasing trend and a decreasing trend were observed in the test range. The results obtained in this study were compared with the results of other studies on thorium radionuclide, which showed a good agreement with other studies.

Severe Accidents Management (SAM) in nuclear power plants is an important safety issue. SAMs require assessing the thermal-hydraulic conditions of the nuclear reactor during the accident. This paper investigates three accident scenarios, Station Black-Out (SBO), SBO with Large Break Loss of Coolant Accident (LBLOCA), and SBO with Small Break Loss of Coolant Accident (SBLOCA) in the WWER1000/V446 reactor using the MELCOR1.8.6 code. The RELAP3.2-SCDAP code is also used to evaluate the accuracy of the reactor pressure vessel parameters.  The purpose of this study was to determine the operating conditions of the reactor during the accident scenarios with emphasis on hydrogen production. The results showed that the SBO has the highest hydrogen production (2150 kg) compared to other accidents and the maximum fuel temperature occurred sooner than the other SAs (11800 seconds). The results obtained by the two codes and the Final Safety Analysis Report (FSAR) of the WWER1000/V446 reactor showed good agreement. The results of this analysis help make the appropriate decision in SAM.

Taking relativistic-ponderomotive nonlinearity into account, the dynamics of an intense Gaussian laser pulse propagating in a multi ions plasma has been studied. The modification of the dielectric permittivity of such plasma due to the ponderomotive force of the laser pulse has been derived. The coupled equations governing the laser pulse dynamics in space and time have been achieved and numerically solved, using the complex eikonal function and paraxial ray approximation. The effects of the initial laser intensity, multiply charged ions, specifically singly and doubly charged ions, on the self-focusing and self-compression of the Gaussian laser pulse in the plasma have been investigated. It was found that there is a particular laser intensity range where self-compression can occur. It was further observed that the multiply charged ions improve or weaken the nonlinear effects depending on the initial laser intensity, which leads to the pulse evolution.

This paper applied two intense relativistic beams to low-density plasma under different conditions. The effect of the distance and the angle between these two beams on the acceleration of electrons were investigated. The simulations showed that when the distance between two beams is zero, and there is no relative angle between them, after some adequate amount of time, it seems that a powerful beam travels through the entire plasma, increasing the acceleration length of the electrons and their kinetic energy. The best overlap occurs between the pulses at and , naturally, the hot electrons will have the highest temperature and the highest cut-off energy. On the other hand, as the pulse distance increases, the useful overlap decreases (the total amplitude of the laser fields decreases). Consequently, the temperature of the hot electrons will reduce. The results showed that the conditions  and  the rate of pulse erosion, and the increase in the kinetic energy of the electrons are slightly greater than the non-zero angles, which can be due to the excitation of the stronger plasma waves.

The purpose of this paper is to investigate the possibility of using fuel with annular geometry (Tubular) in Tehran research reactor (TRR) from a neutronic perspective. The use of annular fuels requires less fuel load due to higher flux generation and higher reactivity. It is noteworthy that one of the most important advantages of this type of fuel is the creation of an area in the center of the fuel complex for irradiation of materials and production of radiopharmaceuticals. Therefore, in the TRR, a new fuel with annular geometry has been adopted to replace the current fuel with cubic geometry. This fuel is similar to TRR fuel in terms of materials. For this purpose, the neutron conditions of the core are simulated using MCNPX2.7 and WIMS-CITATION codes. Then the obtained results from these codes were compared with the SAR results of the TRR. The obtained results in this paper show that to achieve the reactivity equivalent to the first core of the TRR, the critical mass of the tubular core fuel is up to 17% less than the critical mass of the first core fuel. On the other hand, using annular fuel, the neutron flux in the radiation channels increases up to about 14%. Also, according to the results of this study, the proposed tubular core, a core with an arrangement of 16 and at least 8 packages of 6 control rods are needed to achieve safety standards.

In the present study, the total kinetic energy (TKE) values of neutron fission fragments of plutonium isotopes were calculated using the scission point model. The deformation parameters were obtained for neutron fission of plutonium 239, 241, and 242 by comparing the calculated results with experiments in the scission point model. TKE values were evaluated for neutron fission of other plutonium isotopes with these deformation parameters. Using the results of the fission deformation parameters, the average kinetic energy of all neutron fission fragments for the rest of the plutonium isotopes is calculated. The maximum average kinetic energy of all neutron fission fragments for plutonium isotopes is 185 MeV.

This research uses the portable HPGe and NaI(Tl) detectors for Compton continuum suppression.In the List mode data acquisition technique, we did not use timing module and complicated experimental setup that recorded the time stamp of each event. The maximum suppression factor (SF) in Cs-137 point source was 3.8. By using this technique, we can detect samples that contain very low radioactivity. The experimental setup in this research was based on analog nuclear electronic modules. The study's main goal was the ability of list-mode data acquisition in Compton continuum suppression. In this way, lower levels of radioactivity can be detected in any sample.

One of the useful methods for measuring fast neutron decay constant in a nuclear reactor core is the pulsed neutron source experiment as MCNP code is based on the Monte Carlo method, so able to track the time-dependent behavior of the particles in static systems. In this research, this capability is utilized, and a pulsed neutron source experiment in the Tehran research reactor (TRR) core is simulated. For this purpose, the system of TRR core at different subcritical states is investigated, and fast neutron decay constant is estimated at each state. Therefore, kinetic parameters of the reactor core are also calculated utilizing the fast neutron decay constant of the core. Calculated values agree with the other results reported in the literature.

Considering the importance of quality control of radiotherapy systems and 3D dose mapping possibility done with a Fricke agarose gel dosimeter, this dosimeter based on ferrous solution and agarose gel was prepared. The prepared Fricke gel dosimeters was investigated under gamma irradiation with a dose range up to 20 Gy. Concerning the effect of the gel dosimeter constituent’s concentration on the response of the dosimeter, different compositions were surveyed for better sensitivity and repeatability. So, the responses were evaluated for different concentrations of ferrous ion, sulphuric acid, and the indicator. We found that the Fricke agarose gel dosimeter has a linear behavior up to 20 Gy. In addition, the best composition of Fricke agarose gel dosimeter with high sensitivity and stability was determined to be 0.2 mM ferrous, 25 mM sulphuric acid, and 0.15 mM Xylenol orange.