JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY
Year:2018 | Volume:- | Issue:86 |Papers Count:14

In this research work, commissioning of a radiography end station using proton-induced monochromatic X-rays in the Van de Graaff laboratory of Nuclear Science and Technology Research Institute (NSTRI) is reported. An energetic proton beam with a current of hundreds of nanoamps after passing through the relevant slits in the beam path, is used to irradiate a metallic target leading to the generation of monochromatic X-rays. By altering the target, a wide variety of monochromatic X-rays with different wavelengths could be generated. The yield of characteristic proton-induced X-ray emission is measured using a Silicon Drift Detector (SDD). The generated X-rays could then pass through the window of the reaction chamber and irradiate the sample of interest. In this way, the required conditions for radiography by the “ K-edge contrast imaging” could be provided. By implementing the mentioned analytical technique, using the K-edge absorption of the interest element in the sample, radiographic image contrast could be improved for different samples of cultural heritage such as manuscripts, clothes, and coins in the Van de Graaff lab of NSTRI.

Microfluidic chips are commonly used in many industrial and nuclear medicine applications. The biomolecules are labeled with radio nucleoids for increasing the image resolution in nuclear imaging. Labeling of biomolecules with radio nucleoids is an important subject in recent applications of the microfluidic chips. In this paper fabrication of a T-shape microfluidic chip on Polymethylmethacrylate (PMMA) polymer was investigated. The effect of the experimental parameters such as scanning velocity, pulse repetition rate, and laser fluences on the dimensions and the quality of the microchannels were investigated. A two-dimensional T-shape microchannel was fabricated on a PMMA sheet of 1cm×1cm×0. 5cm, under the optimum experimental conditions. A polymer sheet with 2D-microchannels was welded to another PMMA sheet with laser welding for the formation of a 3-dimensional microfluidic chip. Two-dimensional microchannels were fabricated with CO2 and second harmonic of Nd: YAG lasers, both in pulsed mode of operation. Continues and pulse CO2 lasers were both used for welding and formation of three-dimensional microchannels.

Recently, it has been declared that fuel rods do not need to be anodized for the usage in VVER reactors. In this regard, some studies were planned to investigate the effects of pickling and anodizing treatments on corrosion behaviour of the fuel clads produced by Sooreh company. For this purpose, different surface treated samples of as-received, grinded, pickled, grinded and anodized, and pickled and anodized were prepared. The reference fuel clads in some equal conditions were also employed for comparisons. The results revealed that the corrosion behaviour is completely affected by the surface treatment, and microstructure properties have shown less impact. The oxidation type in the pickled, and pickled and anodized samples are absolutely different from the grinded samples. The anodizing treatment after pickling nearly increases the corrosion resistance by factor of two in comparison to the just pickled ones. The presence of grey oxide layer on the grinded samples are attributed to Monoclinic zirconia which has less corrosion resistance to Tetragonal zirconia.

Radiotherapy is the treatment of cancer using ionizing radiation. When a tumor is large in comparison to the range of the ionizing particles, most of the energy is absorbed within the tumor. In cases when the tumor dimensions are smaller than the range of ionizing particles, a large proportion of the energy can escape. Therefore, the tumor size and the range of the ionizing particles are important to be realized in the recurrence probability of tumors. The purpose of this study is to investigate the relationship of recurrence probability to tumor size and paricles energy in external radiotherapy and targeted radionuclide therapy. The absorbed fractions for spheres that ranged in radii from 20 μ m to 4. 5 cm were calculated using the MCNPX code. A mathematical model based on Poisson distribution was used to investigate the relationship of recurrence probability to tumor size for tumors treated with external beam radiotherapy and targeted 131I and 90Y. The results show that for targeted radionuclide therapy, the relationship between the recurrence probability and tumor size is different from that for external beam radiotherapy. The analysis shows that there is a minimum value of the recurrence probability that occures at a diameter of approximately 3. 5 cm for 90Y. For 131I, the minimum recurrence occurs at a tumor diameter of approximately 3. 5 mm. The results show that there is an optimal tumor size for the tumor curability. The recurrence probability has a minimum value for tumors whose diameters are close to the optimum value which depends on the particles energy. Smaller tumors are more recurrence because of the incompetent absorption of radiation energy, i. e., it dose not occure with the external beam iiradiation, and larger tumors are more recurrence because of the greater cell number. The results are shown that single agent targeted radiotherapy should not be used for treatment of disseminated cancers when multiple tumors of differing size may be present. The use of several radionuclides, including long-range and short-range beta emitters, concurrently or from combining targeted radiotherapy with external beam irradiation would be more effective than the reliance on a single radionuclide.

In this study, the thermal decomposition of thorium oxalate dihydrate (Th(C2O4)2. 2H2O) was investigated by using design of experiment-technique. The thermal decomposition experiments were carried out in a two-temperature procedure and the influence of the decomposition temperature of the second step, as well as, durations of both steps on the crystallinity, size, size distribution, morphology and specific surface area of the produced thorium oxide were investigated. For this purpose the experiments were designed by using Taguchi method. The results showed that the optimum decomposition temperature and duration of the first and second heating stages were 400 ° C for 4 hours and 750 ° C for 4 hours, respectively. The powder characterization showed that the cubic thorium oxide particles synthesized in the optimal conditions had uniform size distribution with an approximate size of 350 nanometers. Moreover, the crystallinity of ThO2 phase and specific surface area of these particles were 95% and 35. 23(m2 g-1), respectively.

2-Thenoyltrifluoroacetone (HTTA) has been proposed as a carrier in organic phase for the transport and selective extraction of yttrium using bulk liquid membrane system. The liquid membrane was prepared by dissolving HTTA in dichloromethane. It has been observed that the use of n-propylamine (n-PA) in source phase as a synergistic agent causes an enhancement in transport of yttrium ions. The extraction and stripping conditions have entirely been evaluated and described. The proposed method has been utilized for the separation of yttrium (III) from its binary mixtures with strontium (II) and some other cations such as Ni (II), Co (II), Ag (I), Fe (II), Al (III), Cu (II), Hg (II) and Cs(I) in aqueous solutions of pH 5. 4 in the presence of n-PA, while 1M nitric acid was serving as a stripping agent in the receiving compartment. Cyanide ion and 5-sulfosalicylic acid have been used as masking agents to minimize the interferences from different transition metal ions and Al (III) in source phase, respectively. At the achieved optimized conditions and a discrete experiment, 90Y in secular equilibrium with 90Sr in the source phase, was transferred into receiving phase and separated completely from its long-lived parent isotope.

Layered double hydroxide (Mg/Al; 3: 1) was synthesized by co-precipitation method and used to adsorb uranium from aqueous solutions. Various environmental parameters such as contact time, pH, initial uranium concentration and temperature were investigated. The maximum adsorption capacity occurred at pH=3 (99 mg/g). The adsorption of U(VI) onto LDH decreased with increasing pH at pH>6. 5, because of the formation uranyl carbonate complexes (69 mg/g). The thermodynamic parameters (i. e., Δ H0, Δ S0 and Δ G0) indicated that the adsorption process of U(VI) on LDH was an endothermic and spontaneous process. At pH<6. 5, the probable mechanism of adsorption of U(VI) was governed by inner-sphere surface complexation with OH groups on LDH surfaces, while the dominant mechanism at pH>6. 5 was inner-sphere surface complexation and ion exchange with NO3¯ . Based on the experimental results, LDH is a very suitable material for the removal of U(VI) ions from aqueous solutions in a wide range of pH.

The removal and recovery of uranium from aqueous media has been considered by many scientists and researchers since a long time ago. In this work it has been tried to produce the nano adsorbent that can separate the uranium from nuclear waste waters and the other aqueous media. For this purpose poly(styrene-acrylonitrile) nanofibers and their composite with polycarbonate nanofibers have been prepared and used as adsorbent of uranium after the chemical modification. The chemical modification was performed by the conversion of nitrile groups to amidoxime groups by hydroxyl amine solution and akaline treatment by sodium hydroxide 2. 5%. The amidoximation was confirmed by the infrared spectroscopy. The maximum capacities of uranium adsorption were 79. 8 and 38. 5 mg U/g ads for poly(styrene-acrylonitrile) and poly(styrene-acrylonitrile)/polycarbonate composite, respectively. The optimum pH was 4 for uranium adsorption. The desorption yield was more than 90% in Na2CO3 1M/H2O2 1M solution.

In this paper, separation and purification of uranium from scraps of aluminum oxide fuel plates with combined precipitation methods are reported. In this method, the virtual plate fuel fragments containing U3O8 were dissolved in caustic soda solution. Then, the suspension obtained from dissolution of the aluminum sheath, and particles of U3O8 was reacted with 40% HF solution. The product obtained was subjected to heat treatment to oxidize its U4+ by air oxygen. Next, the uranium in the product oxidized by the leaching process was leached and separated from the impurities and was precipitated in the form of the very pure compounds of AUC and ADU. These intermediaries were converted to pure U3O8 by calcination. The results of the analyses show that U3O8 produced in this way have higher purity compared to U3O8 produced from pure UF6 as well as from U3O8 from defective actual oxide fuel plates which in scientific sources have been purified by the solvent extraction process from the UNH. At the same time, in this method two samples of pure U3O8 powder with grain size of 86% and 94% (above 45 microns) are also produced directly from ammonium bicarbonate leached solutions through formation of AUC sedimentation, the characteristics of which recommend the applicability of this method in terms of chemical purity and grain size of U3O8 produced for enriched uranium in a fuel plate manufacturing line.

One of the main challenges in uranium bioleaching process is events related to improvement, acceleration and enhancement of the extraction. One of them is to provide a favorable environment and biological conditions for Acidithiobacillus ferrooxidans. While, the nutrients of bacteria medium have a significant impact on the activity and growth of bacteria, in the present study, two selective culture mediums were used in uranium bioleaching process at pulp densities of 2. 5 and 12. 5 %. The media are containing the usual 9k and enriched 9k medium with peptone and TSB (Tryptic Soy Broth). The uranium bioleaching process using the selective 2 media with different pulp densities were performed under optimum conditions. The results indicated that the uranium extraction at 2. 5% pulp density, using the 9k-New medium and 9k medium, have carried out during 2 and 3 days, respectively. In addition, at 12. 5 % pulp density, the total uranium in the ore was extracted during 3 and 7 days using the 9k-New and 9k media, respectively. Eh variations showed that the Eh in the 9k-New medium in compared with the 9k medium were increased 13-22%. According to the results obtained in this study, it is concluded that the use of nutrients such as peptone and TSB have significant impacts on the activity of bacteria and also the speed of uranium extraction. Thus, the optimization of the 9k medium using peptone and TSB is recommended for the uranium bioleaching process.

Blast disease, caused by fungus Magnaporthe grisea (Hebert) Barr, with asexual form Pyricularia grisea (Cooke) Sacc, is the main fungal disease of rice in the tropical and temperate regions of the world and also in Iran. Mutant plants derived from mutation breeding due to having the same genetic background with their wild-type are useful experimental material for comparative analysis and dissecting molecular mechanisms. For this purpose, seeds of two rice genotypes, including mutant variety (Pooya) and its wild-type parent cultivar (Mosatarom), were prepared from the Rice Research Institute of Iran and used in greenhouse tests. Evaluation of resistance components showed that Pooya mutant variety was resistant and Mosatarom cultivar was susceptible. The biochemical analysis under control and inoculated conditions revealed that the enzyme activities of catalase, peroxidase, polyphenol oxidase in the Pooya mutant variety were more than, while the TBARM index was lower than, the Mosatarom cultivar. According to the positive role of defense enzymes in controlling disease progression, the Pooya mutant variety had better than its wild-type parent cultivar against the blast disease, due to the maximum defense enzyme activity.

In this paper, the MCNPX code is applied for feasibility study of using the Isfahan MNSR as a neutron source to be used for neutron radiography. To produce a good neutron beam, in terms of intensity and quality, aluminum (Al) with a thickness of 0. 7 cm, bismuth (Bi), and lead (Pb) with a thickness of 1 cm are used as a fast neutron filter, and the gamma filter, respectively. The L/D ratio of the designed neutron radiography facility is 90 and the diverging angle is 2. 1 degree. The thermal neutron flux, the ratio of thermal neutron to gamma dose rate, and the thermal neutron content at the beam exit plane are evaluated to be 1. 47E+05 n/cm2. s, 2. 96E+06 n/cm2. mR, and 92. 5%, respectively. It was realized that if such a thermal neutron beam is built in Isfahan MNSR, many practical and scientific applications of the NR can be realized.