JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY
Year:2020 | Volume:41 | Issue:2 (92)|Papers Count:20

Online elemental analysis of irradiated tissue in proton therapy is a major part of this treatment, since it leads to accurate estimation of the depth of Bragg peak, proton range, and distribution of stopping power of irradiated tissue. Given the fact that each element has unique characteristic prompt gamma (PG) spectrum, recording and analyzing of the emitted gamma-ray spectra is one of the methods used for online elemental analysis of irradiated tissue. In the present study, the PG lines of most abundant elements of human tissues (12C, 16O, 20Ca, and 14N) are obtained using Geant4 toolkit. Moreover, the linear dependency of 7. 12, 3. 91 and 2. 31 MeV PG counts to the mass of 16O, 20Ca, and 14N are investigated in five phantoms. The gamma lines of 2. 31, 3. 91 and 7. 12 MeV are selected to determine the mass of nitrogen, calcium, and oxygen in the irradiated volume. Furthermore, for two test phantoms, the mass of elements is estimated using linear fitting and is compared with predefined mass of these elements in the test phantoms. The results showed that the relative errors of estimated mass of calcium, nitrogen, and oxygen are less than 6%, which leads to the range estimation deviation of about 1 mm.

In this research, nanocrystalline powder of SrSO4: Sm was prepared by chemical co-precipitation method at room temperature. The SrSO4: Sm nanocrystalline powder was characterized using X-ray diffraction (XRD) and energy-dispersive x-ray spectroscopy (EDX), thermoluminescence (TL) and photoluminescence (PL). Under UV irradiation, all samples had a main peak at 220˚ C. The advantage of this nanocrystalline powder is a simple TL glow peak in the temperature above 200˚ C for UV radiation dosimetric. The results showed that changing Sm concentration affected the TL glow curve intensity and the maximum intensity of the TL glow curve of SrSO4: Sm was obtained for Sm with 0. 15 mol%. The TL response of the SrSO4: Sm irradiated with different UV irradiation time showed a linear behavior from 10-90 minutes. The fading of this nanocrystalline powder was less than 16% for 4 weeks. Moreover, the emission spectra of the SrSO4: Sm nanocrystalline powder under excitation wavelength 320 nm showed peaks in the 690 and 725 nm wavelengths which were related to 4G5/2-6H11/2 and 4G5/2-6H13/2, respectively.

The cyclic tetrapyrrolic compounds, such as porphyrins, play an important role in medical research due to their fundamental role in the body of living beings, the ability to accumulate in various human cancer cells, as well as having distinct physical, magnetic, and optical properties. Therefore, they are very useful in the design of anticancer pharmaceuticals and photodynamic therapy agents. Due to the prominent properties of gallium-68 and the targeted accumulation of radachlorin anticancer drug, the radiopharmaceutical complex of this porphyrin is synthesized with gallium-68 radionuclide and its biological information such as partition coefficient and biodistribution studies in normal and tumorbearing rats were studied. The complex was prepared with acceptable radiochemical purity and stability in the final formulation and human serum for 4 h. The partition coefficient was-1. 14. High accumulation of the complex in the tumor, rapid washout from the body, and lower absorbed radiation doses to patients were observed using this labeled compound. In this study combining the unique reactivity of gallium-68 with flat-lipophilic ligands with a neutral electric charge, such as radachlorin, the potential for betaexcretion for PET, and the use of radachlorin in PDT for therapeutic purposes, a new PET / PDT imaging agent was introduced.

In the treatment of the tumors using proton therapy, the synchrotron emits a monoenergetic beam that transports most of its energy in a special position after entering the target. There are two approaches to invading the entire tumor tissue. One of these methods, which the present work deals with, is known as passive scattering. The proton beam should be passed through a rotating scatterer, called modulation wheel, to cover the total volume of the tumor. This scattering device, in its turning, places different thicknesses of materials on the path of the proton and converts this monoenergetic beam to a spectrum with lower energy. This beam is absorbed in the lower depth of the tissue. The goal of this approach is to achieve an energy absorption curve with a maximum flat area in the tumor volume and a fast reduction to zero after passing through the tumor. Investigating the effect of materials and the geometric changes of the dispersive components in the path of the proton beam is a significant issue affecting the shape of the absorption curve. Using the Geant4 toolkit which is based on the Monte Carlo method, this dispersive system was simulated. The calculation of the geometric characteristics of the range modulator wheel, which leads to a flattened absorption curve in the tumor area, has been studied in the literature. In the present work, a Python program with an iterative algorithm has been written to design an acceptable plane curve.

In this study, the effect of control rods on TRR safety parameters was investigated in both cases of static and transient behavior. In this paper, the effect of the control rods movements (70%) on the power peaking was used in the form of the normalized function instead of the COS function in the TERMIC cod. The results of the new function were investigated on thermo-hydraulic parameters in the steady-state and transient conditions. In the steady-state with 5 MW thermal power, the results showed that the safety margin in new condition (70% insertion) decreased respect to the state that all control rods where out. Also, in the transient section, the axial function of the power distribution was applied in the input of the PARET cod. The direct influence of control rods on the power peaking was the production of nucleate boiling earlier than the COS shape function. This effect, reduced the power and temperatures due to the void coefficient feedback. In the last section, the effect of the control rods insertion on the reactivity feedback coefficient was considered in the transient scenario. Increment of the reactivity feedback coefficient due to control rods insertion along with the direct effect of control rods caused a significant decrease in all thermo-hydraulic safety parameters.

Measuring volume fractions and identifying the flow regime are important challenges in the oil industry. In the present study, three different flow regimes were simulated by MCNPX code. A 137Cs source and two NaI detectors have been used in order to count the transmitted photons. The counted data had high-frequency noises. In order to tackle this problem, a Savitzky-Golay filter was applied. Therefore, four features in the time domain including STD, Skewness, Kurtosis, and Maximum Value were extracted. It was found that the extracted features are not capable of separating the flow regimes completely, without overlap. Accordingly, three different features from registered data of both detectors were extracted. After investigating all the possible statues, two ANNs were implemented to identify the flow regimes and predict the void fraction, respectively. By applying this method, all the three flow regimes were correctly distinguished and void fraction was predicted with root mean square error (RMSE) of less than 0. 59.

In this paper, the magnetic probes assembly of Damavand tokamak which is being used for measurement of local magnetic fields, were utilized as a discrete Rogowski coil inside the vacuum vessel. An important advantage of this approach is the insensitivity of the new Rogowski coil to magnetic fields created by the external ohmic and equilibrium coils. Thae theoretical basis for the calculation of magnetic fields in the space between two probes was discussed and verified with experimental data. The lowest error was obtained in the second-order finite element computational method for discretizing Ampere's Law Integral. Moreover, the stability of measured currents considering error for magnetic field measurement was investigated. According to the results, it was found that Damavand Tokamak magnetic probes with the finite element second-order calculation method could be used as a more accurate discrete Rogowski coil than the machine main Rogowski coil.

In this paper, the design and simulation of ion source based on a helicon plasma generator and its corresponding extraction system for design of the neutral beam injection heating system of a sample tokamak like Damavand tokamak using COMSOL software have been investigated. Based on our previous calculations, to increase the electron temperature of this tokamak to 300 eV and the ion temperature to 150 eV, it requires a neutral beam injection system with energy 4. 5 KeV, 6. 7 A current, and 30. 15 kW power. In this regard, in the present model, a dense helicon plasma source with an electron density of 5. 51×1018 m-3, an electron temperature of 2. 8 eV and an extraction system with 280 holes (3. 5 mm in diameter) and 7 A ion beam for this heating system were designed, simulated and presented. Also, in this design, all the optical issues of the ion beam such as divergence, space charge, and beam size which can affect the beam quality are investigated.

In the present research, we addressed the investigation parameters of the two proposed cascade models for separation of multi-component mixtures (Matched-X and Pseudo binary type 1 cascades) to separate Te-123 isotope. Besides, we compared their performance by changing parameters k, k1, and k2. The results showed that for a cascade with 10 stages and feed stage 5 and feed flow rate 100 g. s-1, the minimum total interstage flow of the matched-X cascade occurs in the condition k = 7, k1 = 1 and k2 = 3, with the amount of 1881. 133 g. s-1. In this case, the concentration of Te-123 in the product stream of the cascade is equal to 0. 0349 while the maximum product concentration of Te-123 occurs at k = 1, k1 = 1 and k2 = 2 with the amount of 0. 0389. In this cascade, the total inter stage flow is equal to 2159. 914 g. s-1. Also, the results represented that in the Pseudo binary type 1 cascade, the minimum total interstage flow and maximum product concentration of Te-123 occur at the same time, in the condition k = 1, k1 = 1 and k2 = 2 with the amounts of 2159. 914 and 0. 0389 g. s-1, respectively.

Due to the increasing need for Oxygen-18 isotope in medical centers to produce 18F radioisotopes used in positron emission tomography (PET) centers, research is today more necessary than ever to improve and increase the production efficiency of this isotope. The concentration of oxygen-18 in water is 5. 4% in this study, in a pilot distillation tower and in a total reflux state, two packings of coated Dixon and coated Sulzer have been tested in different return flows. The results showed that the pattern of Height Equivalent to a Theoretical Plate (HETP) variations for these two packings, which are irregular and regular packings, respectively, were significantly different from each other and of course, the amount of HETP obtained for coated Sulzer is less than coated Dixon. Accordingly, using coated packing Sulzer requires fewer equilibrium steps to achieve 99% purity of oxygen-18 isotope.

In the present work, the results of using a low energy plasma focus device MTPF-2, in order to investigate the destructive effects of shockwave and high-energy ions on tungsten and copper surfaces, are presented. Tungsten and copper were selected as a relatively hard and soft metals, respectively. The samples were placed at a distance of 8 cm from the upper anode surface at zero degrees relative to the symmetry axis and were exposed to ions and a shockwave from 20 electrical discharges. The discharge voltages were 12 kV and carried out in hydrogen gas at a pressure of 1mbar. By using the optical microscopy images, scanning electron microscopy images, x-ray diffraction spectroscopy, and x-ray diffraction analysis, the reference and irradiated samples were analyzed. The results, in addition to confirming the performance of the MTPF-2 device to be used in such studies, showed that the collision of ions and the shockwave creates, cracks and blister at the surface of the tungsten, lead to the creation of cracks, blisters, and melting of the copper surface, and changing the crystalline parameters such as the Bragg angles, the intensity of the peaks of the diffraction spectrum, and the distance between the crystalline plates. The calculations, which were performed by using the Scherrer’ s formula also show a change in the average grain size of both metal surfaces.

Narigan area in the southern part of the Bafq-Saghand metallogenic zone in Central Iran is a host of davidite-bearing quartz veins. Davidite is an important key mineral for exploration of not only uranium but also REE's in Central Iran. Narigan granite in the Narigan area is characterized by high-K calc-alkaline nature and its parental magma was partially contaminated by the Precambrian crust. The REE pattern of quartz veins is brought about by REE contents in davidite. The homogenization temperatures of vapor-liquid-solid (V-L-S) fluid inclusions in quartzes are >500˚ C in quartz veins. Furthermore, the Σ REE contents (71910 to 90292 ppm) and U/Th ratios (<1000) in the studied davidites indicate upper 450˚ C temperature for the generation of them. Based on the similarity of REE pattern of davidite to REE pattern of oxide-uranium minerals in the vein-type ores (characterized by negative Eu anomaly and high LREE/HREE ratio) as well as achievement of the homogenization temperatures for fluid inclusions and davidite formation; mineralization of this mineral can be related to granite related vein-type uranium deposits.

Nowadays, to mitigate global warming, soil can play a significant role as a pool of terrestrial carbon. Therefore, the objective of the study was to investigate the effect of climate on the radiocarbon Mean Resistance Time (MRT) in surface and subsurface soils in some of rangelands of Khuzestan Province, Iran. This way, rangelands were selected under different climates in two regions called Izeh and Ramhormoz. In both regions, the control profiles were studied to determine physical and chemical properties of the soil, carbon forms and 14C (carbon-14 isotopic ratio). The results showed that the MRT of the corresponding depths of Ramhormoz profile (with lower mean annual rainfall) was far higher than those of the Izeh profile, due to higher turnover of fresh organic matters in Izeh rangeland. Unlike Izeh profile, the MRT in Ramhormoz profile did not increase with depth owing to clay content and topographic position of the region i. e. being a depositional site. Overall, the age of carbon-14 in the top horizons of the study areas was mostly affected by factors such as climate, land management and the presence of decomposition sensitive forms of carbon. While, in deep soil the age of carbon was affected by other factors, especially soil taxa, clay content, topographic position (erosional or depositional sites) and discontinuity in soil parameters such as bulk density than by climate.

Monitoring the power distribution of reactor core is one of the most challenging issues in the safe operation of nuclear reactors. The Number and arrangement of detectors in a core monitoring system should be determined in a way that maximum amount of information about core states is extracted, while avoiding duplication of similar and correlated measurements. Information theory is the best method to deal with the problem of optimal number and placement of instruments. In this paper, the effects of reactor fuel burn-up on the optimal number and arragement of in-core fixed detectors of Tehran Research Reactor has been investigated using information theory. Comparison the results for the two modes, with and without consideration of the fuel burn-up, shows that by considering fuel burn-up in the placement problem, more information can be extracted from measurements of the detectors. Also, for an equal number of detectors, determined arrangement by considering fuel burn-up, mostly provide larger share of total available information in the data set. Using the optimal arrangement, maximum information can be obtained from minimum number of the detectors, which leads to considerable decrease in the cost of construction, implementation, operation, and maintenance of the in-core detectors for monitoring of neutron flux.

For the prevention of energy crisis after finishing the uranium earth sources, the study on the alternative sources is necessary and unavoidable. Seawater contains uranium about 1000 times more than that of the earth which is one of the most important sources. In the present work, at first, the free radicals were created on the polyethylene and polypropylene micro hollow fibers at very low temperatures via pre-irradiation electron beams by Rodotron accelerator and then, the acrylonitrile and methacrylic acid immediately were grafted on these fibers. To investigate the solvent and concentration effects, the grafting solutions were prepared with the different concentrations by DMSO and DMF solvents, and then, the radiated micro hollow fibers were immersed into them. The best grafting percentage was 90% corresponding to the polypropylene micro hollow fibers in the grafting solution with 60 to 40 for the monomer to solvent volume ratio. The nitrile groups were converted to the amidoxime groups by the hydroxylamine 10% within 72 hours at 80oC. By using the gravimetric method, the amidoximation degree was 80%. The grafting and amidoximation steps, and the surface morphology of fibers were characterized by FTIR spectroscopy and SEM, respectively.

The performance of a uranium gas centrifuge which is used in the uranium enrichment industry depends strongly on the gas flow field. The computer simulation is vital to examine the gas flow field. Therefore, in the present study, the capabilities of OpenFoam software for simulating the gas flow inside the rotor for total reflux thermal drive-in axisymmetric mode has been investigated. The results corresponding to the OpenFoam ssimulation have been validated with those of analytical Olander’ s model, numerical solution of the Harada’ s study, and simulation using Fluent. The simulation results for gas flow inside the rotor of centrifuge showed that the density-based solver was properly chosen and the number of cells, 160×170, was compatible with mesh. The numerical results show that OpenFoam software was capable to examine the gas flow inside the rotor. Also, the simulation of the distribution of Knudsen number confirms the presence of the molecular region near the axis of rotation. OpenFoam is open-source software and there is the ability to solve the molecular region as well as the coding for coupling the continuous and molecular region, the feature which does not exist in the fluent software. The use of open foam is therefore recommended to simulate gas flow inside the rotor.

Vision-RT system is one of the most effective methods for real-time estimation of target location in external beam radiotherapy. Vision-RT tracks the patient’ s surface before and during radiation therapy to improve treatment accuracy. Using proprietary 3D stereo camera units, Vision-RT system tracks the skin surface, compares it to the ideal position, and can automatically signal to the treatment delivery system. The purpose of this study is to investigate the accuracy of Vision RT guided deep inspiration breath-hold left-sided breast cancer radiotherapy. Five patients with left-sided breast cancer were treated by Vision RT guided deep inspiration breath-hold at Aarhus university hospital. Based on the results, in one out of five patients, the undesired heart extended to 0. 6-0. 9 cm into the treatment fields in 5 out of 15 treatment fractions. Moreover, the required PTV margin to account for patient setup error and intra-fractional error of the first and second treatment field was 2. 38 mm, 3 mm and 4. 12 mm, respectively.

In uranium mines, the excavated waste has a lower grade than the threshold grade and is dumped on the surface as waste material. Due to erosion and rainfall over time, it is very likely that part of the uranium content is washed out of waste dump and leaked into surface and subsurface water resources and cause severe environmental hazards. The excavated waste during mining, as well as water collected during the drainage process of underground excavations, can be reused in the preparation of concrete fillers. In this study, samples of concrete backfill material were prepared by using waste material excavated from Saghand open pit and underground mines. Based on conducted testing and analyses, it was found that a large proportion of deposed waste and drained water can be used to prepare concrete fillers to fill stopes in Saghand underground mine. This process leads to a major reduction in mining costs, increased safety of mining operations, and significant improvements in reducing environmental pollutions.

The chemical isotope exchange with macrocyclic polyethers is one of the relatively new methods for isotope separation. These separations are based on the phenomenon of isotope effect, in which the kinetic and the stability of the complex formation between the ligand and the isotopes of an element are different. In particular, crown ethers and cryptands, with high affinity and size selectivity for some metal ions, have been investigated for isotope separation in various extraction processes. In the present study, the isotope effect in a solid-liquid extraction of strontium with Merrifield resin having 2. 2. 2-Cryptand anchor groups was investigated. The effects of various experimental parameters such as pH, concentration of strontium, type of anion, equilibrium time, and temperature on the separation factor of strontium isotopes were studied and discussed. The results showed that the separation factor had an inverse correlation with the isotope mass and for the lighter isotopes this factor was greater. Under the optimum conditions, the separation factors for 84Sr/88Sr, 86Sr/88Sr, and 87Sr/88Sr were 1. 028, 1. 017, and 1. 014, respectively.

The data acquisition system of the Alvand tokamak is a very old system of 32 channels. The data capacity of each channel is 2 kilobytes, altogether 64 kilobytes, which store the experimental data of selected channels in binary format. The most important deficiency of this system is the use of the CGA graphic adapter resolution of 320240× pixels of 4 bits in-depth. By considering the old graphical user interface, this deficiency has made displaying the experimental data in more detail impossible. Due to the old software used to display the experimental data, updating to an appropriate graphical environment, that can display the data on a typical modern computer at this laboratory, is necessary. For this purpose, a software package was developed to speed up the data analysis of experiments. The core of this package includes 400 lines and the graphical user interface consists of 3000 lines of Matlab code.