JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY
Year:2018 | Volume:- | Issue:83 |Papers Count:11

The distribution of the magnetized magnitudes of the flowing nuclear spins has a key role to evaluate the radiofrequency pulses used in the magnetic resonance angiography (MRA). In this study, a finite difference method is used to solve Bloch equations for the flowing nuclear spins during and after a 90° rectangular selective pulse which is important for optimization of the pulse sequence. The results of the simulation indicate that the magnitudes are deformed due to the flowing nuclear spins, while their velocity is increased. The maximum variations are created on the transverse magnitudes namely, Mx and My. The symmetry on these profiles disappear by increasing the velocity. In contrast, no variation on the longitudinal magnitude namely Mz is observed, except a shift on the velocity direction. The sensitivity of these profiles at low velocities for the rectangular selective pulse is more than that of the sinc type, which probably it may be used for characterizing the capillary space. In general, one may obtain the distribution of magnitudes for pulses with various flip angles, as well as, the combination of different pulses. The results may be employed to improve mapping indices in the MRA as well as assessment pulse sequences on the flowing nuclear spins.

Detailed recognition of dose distribution around the brachytherapy sources in order to create appropriate plans for treatment of cancer is very important. In this study, with calculation of the dosimetric parameters of clinical 252Cf source based on TG-43U1 protocol and utilizing different tallies of dose calculation in MCNPX code [F4 (Fluence Tally), F6 (Kerma Tally) and *F8 (Dose Tally)], the dose rate at different directions and distances from the source center has been determined and compared with other experimental and simulation results. By comparing the results of this study with the experimental measurements and observing the good adaptation of the results, it was observed that the dose rate of clinical 252Cf source has its largest value at the direction of longitudinal axis of the source, which is the reason for more expansion of radioactive material distribution in this direction, in comparsion with other directions and consequently higher neutron flux in this direction, based on the angular dependance of dose rate to geometric function according to TG-43 protocol. It was also found that the F4 and F6 tally results in neutron dosimetry calculations are more accurate than the *F8 tally results. The dosimetry calculations performed in this study has provided a preliminary dosimetry characterization of 252Cf neutron sources for usage in treatment plans in the country.

Systems related to reactivity control in a heavy water zero power reactor (HWZPR) consist of safety rod, control rod, emergency dump, and water level measurement and regulation systems. The control rod reactivity worth and safety rods should, therefore, meet the necessary safety criteria. The safety rods are used to shutdown the reactor through rapid falls in the emergency of the reactor and for a normal shutting down condition. According to the safety criteria, the equivalent rod reactivity worth must be appreciably greater than the maximum excess of reactivity which occurs in a reactor. The main applications of the control rods are to control the power rising period and the transition from subcritical to supercritical states. According to the safety guide for a HWZPR when a reactor is close to the critical state, the reactivity insertion rate should not exceed 2×10-4 (Δ k/k)/s and the reactivity worth of each control rod should be less than 0. 2% Δ k/k to ensure the safety of the reactor operation. According to the obtained calculational and experimental results, these conditions are satisfied for HWZPR. By changing the reactor fuel from natural metal uranium to mixed fuel (natural metal uranium fuel and natural oxide uranium), the control rod reactivity worth is measured and according to the obtained results, the control rod reactivity worth can meet the above provisions.

In this article, after a brief introduction of MTPF-1 plasma focus device, some of the related experimental data are presented. These data show that it is possible to select the proper gas pressure and discharge voltage in order to have a specified pinch time interval. In addition, the effects of gas pressure and discharge voltage on the current sheath’ s mean velocity have also been studied. This study showed that, in the case of argon, the maximum value of the current sheath’ s mean velocity is about 5 cm/μ s, where it can be obtained under various combinations of the pressures and discharge voltages. By using the speed factor concept, the velocity of the current sheath at the pinch time was also examined. It was determined that in two separate experiments with different gas pressures and discharge voltages, the equality of the pinch times means the approximate equality of the current sheath radial velocities.

In current study, sampling from Baghak mine in Sangan mines has been carried out based on radioactivity and radiation measurement method. In most projects that have been carried out in Iran for the uranium prospecting, especially in the central part of Iran, enrichment of rare earth elements (REEs) are known in keeping with uranium as a common feature. The association of these elements with U has caused to investigate their connections with other types of mineralizations. In fact the goal of this study is to survey the presence or absence of such a connection in a skarn mine which is a different case study from the central part of Iran. In case of their presence, this will lead to a new exploration method and sampling pattern for REEs. The results show that in addition to existence of this connection in some mineralizations of the Central Iran, an acceptable correlation is also observed between the REEs and radioactive elements in another iron skarn deposit. Finally, it can be explained that according to existence of such a connection between rare earth and radioactive elements in several different types of mineralizations, and based on the geochemical similarities, the need for more accurate studies is completely felt in order to introduce radiation measurement methods as effective approaches to explore REEs. The idea and the introduced method for the exploration of REEs in this study can provide a new viewpoint for the decision makers in this industry upon using further studies in this respect.

Increasing of the global energy demand, effects of greenhouse gases emissions and restrictions on the use of renewable energies, will inevitably lead to rise again nuclear energy in the future. Due to the importance of energy security and the sustainability of resources, better waste management, as well as the inability to use nuclear proliferation, many countries have focused on the use of Thorium fuel in the nuclear energy field. It is very difficult to select appropriate technologies and make the right decisions about investing for R & D managers and policymakers because of resource constraints. The aim of this study is to use the technology roadmapping to support the development of the Thorium fuel pellets fabrication technology planning. First, the types of technology roadmapping processes were identified and T-plan approach were selected. Next, by holding workshops and expert panels, the type of fuel pellet, mixed Thorium with 4. 8% enriched Uranium oxide pellet, was selected among carbide, oxide and metal fuels and its functional characteristics determined. Based on the technology importance, which was considered as capability and attractivity indicators, sedimentation and sol-gel methods were selected for powder production technologies, and SGMP and powder metalorgy methods were chosen because of their priorities. Finally, with the suggestion of research projects for the acquisition of technical knowledge of Thorium Fuel pellet fabrication, the technology roadmap was developed.

In this study, the feasibility of vanadium recovery from magnetite ore (Anomally II) of Saghand area in the central part of Iran was investigated. Alkaline roasting-acid leaching process was applied to separate and extract vanadium from magnetite ore. Initially, ore samples having dimensions of less than 100 microns were crushed and grounded. The roasting stage was conducted by placing the sample mixed with certain sodium carbonate (salt) in a muffle furnace at a certain temperature and time. The roasted sample was leached in sulfuric acid at a certain temperature, the liquid to solid ratio (l/s), as well as the concentration of acid and time. In this research, the effect of roasting and leaching different parameters on the vanadium recovery from magnetite ore was determined. The results showed that the optimum temperature, time and sodium carbonate content in the roasting process were 1000˚ C, 2 h and 40 wt%, respectively. Also, values of concentration of sulfuric acid, temperature, liquid to solid ratio and time were optimized for the leaching process. The maximum vanadium recovery of 87. 8% was achieved under the optimum leaching condition of 85˚ C, L/S: 10/1, sulfuric acid concentration: 4M and leaching time 5h.

The separation of zirconium and niobium from lanthanides in hydrochloric medium and the selective transport of them via bulk liquid membrane (BLM) was examined. Tri-n-butyl phosphate (TBP), tri-n-octylamine (TNOA) and dibenzo-18-crown-6 (DBC 6) diluted in kerosene and benzene were used as a carrier. The various effects on the transport and separation of zirconium (IV) and niobium (V) were studied: concentration of hydrochloric acid in the feed and strip solutions, type and concentration of the carrier (TBP, TNOA, DBC 6) in the membrane phase. The extraction of zirconium (IV) and niobium (V) in the membrane phase from 9. 0 M hydrochloric acid by 30% (v/v) TBP was achieved by leaving lanthanides in the feed solution. The quantitative recovery of zirconium (IV) and niobium (V) were achieved by 0. 5 M HCl. Furthermore, the transport kinetics study showed that niobium transport process exhibits slightly faster kinetics than zirconium. The kinetics of Zr(IV)/Nb(V) transport were investigated assuming a consecutive, irreversible second-order reaction on the interfaces. It was found that the rate constant of niobium (V) transport from the donor phase-to-the membrane and from the membrane to the acceptor phase was, respectively, about 98 and 24% more than the zirconium (IV) transport rate constant.

Diglycolamides have been widely investigated for the high efficient extraction of lanthanide and actinide ions from nuclear wastes. In the present study, we have mainly investigated the structural changes of diglycolamides and their interaction with trivalent lanthanum cation from the structural, electronic and thermodynamical viewpoints, using density functional theory (DFT) approach. In this line, we have assessed comparatively some structural changes in diglycolamide ligand, including displacement of oxygen ether with nitrogen, using methyl substituent and also adding methylene between oxygen ether and carbonyl functional group. The calculated thermodynamical properties indicate that addition of methylene groups between the ether oxygen and carbonyl functional groups decreases the performance of these ligands in the extraction of lanthanum ions. Moreover, our calculated results demonstrate the thermodynamical preference of using n-hexane as solvent in comparison with dodecane that is in agreement with the experimental observations. In the next step, the trend of variations in the calculated bond order of some selected key bonds through the complexation process has been analyzed. Finally, we have calculated and discussed the deformation energies of ligands through the complexation with the lanthanum cation.

In order to evaluate the mutant lines derived from irradiation of oilseed rape cultivar RGS003 using gamma-ray, this study was carried out during two growing seasons from 2011 to 2013, at the experimental fields in the Nuclear Agricultural Research School. The experimental design was a randomized complete block design with three replications. Significant differences were observed between mutant genotypes and cultivars for grain yield during two years of the experiment. Interaction of year × genotype (GE) showed a significant difference. Identification and selection of mutant lines, especially in the quantitative traits due to the interaction of genotype and environmental effects, is very important and complicated. The biplot method is an effective approach for the selection of mutant lines, based on the traits and yield stability over the time. The aim of this research was selection of the superior mutant lines from of 32 mutants, using the GGE biplot method. The mutant lines RG16, RG14 and RG31 showed high and stable grain yields compare to other mutant lines and cultivars. According to our results, mutation breeding can be used effectively in oil seed rape improvement.