JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY
Year:2015 | Volume:- | Issue:71|Papers Count:18

In this study, an adsorbent material of poly vinyl alcohol (PVA)/ titanium oxide (TiO2)/ amino-propyltriethoxysilane (APTES) was synthesized by the casting method. The FTIR spectra indicated that PVA/TiO2/APTES nanohybrid adsorbent was functionalized by amine groups. The SEM analysis also showed that the TiO2 nanoparticles were dispersed well on the adsorbent surface. Several influential variables such as TiO2 content, APTES content, pH, contact time, initial concentration and temperature were studied in a sorption batch mode. The optimum conditions for thorium were specified in 20%W of TiO2, 10%W of APTES, within the contact time of 5 hours, adsorbent dose of 1 g/L, temperature of 45oC and pH of 5. The kinetic data were fitted to pseudo-first-order, pseudo-second-order and double-exponential models. Based on the results, the double-exponential model described the experimental data well. Three isotherm models, namely Freundlich, Langmuir and Dubbinin-Radushkevich were used for analysis of the equilibrium data. Based on the results, the Freundlich isotherm was better than other isotherms. The maximum adsorption capacity of the nanohybrid for thorium was 43.7 mg/g. Calculation of thermodynamic parameters showed that the nature of thorium sorption onto the nanohybrid was endothermic and spontaneous. The change of adsorption capacity after five sorption- desorption cycles was less than 20%.

Both of the LaBr3:Ce and NaI (Tl) detectors are inorganic scintillators that due to their high light output rate in comparison with organic scintillators and almost other inorganic scintillators are significant. In this research, experimental data for identical measurement of the sealed button sources with both detectors in the presence and absence of the shield were compared with the simulation data by using MCNP 4C code for the crystals of detectors. The obtained results from the radioactive sealed button sources measurements represented that for low energy gamma rays there are noticeable differences between the experimental and simulation data and that is highly due to non-negligible and effective attenuation of these low energy gamma rays in passing through the window and the shield of detectors included the crystals. The high energy gamma rays simulation data are, however, in agreement with the experimental observations. Also, all the simulation data as well as the experimental measurents showed that the efficiency of the LaBr3:Ce detector is higher than that of the NaI (Tl) detector. The simulation results for the shielded button sources are also in agreement with the experimental data in most ranges of gama energies.

Nb3Sn superconductor compound is the most widely used material for generating magnetic fields above 10T. But, this intermetallic compound is obtained by thermal reactions at high temperatures (>2000oC). Therefore, in recent years the researchers have investigated the processes that permit the formation of the Nb3Sn superconducting phases at lower temperatures (<1000oC). The aim of this study was preparation of nanocrystalline Nb3Sn intermetallic compound using mechanical alloying and heat treatment at low temperature. The phase transitions of milled powder before and after the heat treatment were characterized using X-ray diffractometry (XRD). The microstructural analyses were performed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The grain size and lattice strain were calculated using the Williamson-hall method. During the milling, mechanical alloying of Nb-Sn elemental powders resulted in the formation of a solid solution, while the heat-treatment led to the formation of Nb3Sn phase. The results showed that Nb3Sn XRD peaks appeared after the heat treatment at 600oC for the powder milled for 10h.

The adsorptive removal of heavy metals (U, Ni and Cu) from Esfahan Uranium Conversion Facility (UCF) wastewater was studied in the laboratory by means of batch method using a magnetic biosorbent composed of nanoparticles of magnetite coverd with sugarcane bagas. The findings indicated that the prepared magnetic biosorbent is suitable for the removal of heavy metals. Furthemore, pH of 5 and equilibrium time of 90 min were adequate to set out the optimum condition of heavy metal biosorption process. The kinetic data were fitted well to a pseudo-second-order rate equation. On the other hand, the results showed that biosorption capacity is decreased by increasing the biosorben dosage. The FT-IR analysis of the adsorbent before and after entering into the contact with wastewater showed that functional groups of hydroxyl, carboxyl and amine have the most important role in the heavy metal biosorption.

One of the main requirements in plasma focus researches is determination of the type and energy range of the produced ions in order to use them in applications and theoretical research activities. Furthermore, Thomson Parabola Spectrometer (TPS) is a very useful tool for measuring ion energy spectrum in a complex radiation field. At first, a typical TPS was built and tested. Then due to bugs in the prototype, a new TPS was designed and constructed with more accuracy and resolution. Some experiments were performed on the two different plasma focus devices by both spectrometers. The results of the new device showed a good performance in separating ions. The two types of CST and SRIM software were used to simulate different parts of this device. The results of the simulations and experiments showed a good agreement and the reliability of CST software for ion beam transport in TPS systems. CST enables us to set the parameters of the system before an experiment and also to diagnose the ions after the experiment.

In this study, DNA damage and statistics of hit in any compartments of B-DNA conformation of genetic material of living cells, induced by monoenergetic electrons, have been studied using Monte Carlo Geant4 (Geometry and tracking 4)-DNA toolkit. Simple 34 bp segments of B-DNA conformation, repeated randomly in high number, and monoenergetic electrons (1-20 keV) have been simulated in a volume of typical animal cell nucleus. The average yields of single strand and double strand damage for this energy range of electrons were 24.6 Gy-1Gbp-1 and 0.295 Gy-1Gbp-1, respectively. The highest hit efficiency is for phosphodiester volume of B-DNA model and the most single strand break damage yield has been calculated for 8 keV electrons. The averaged DSB to SSB fraction for this energy range electrons is about 0.031.

Developing of new infection imaging agents is a mandate in the detection of resistant species in the clinic due to the mortality of various new strains of bacteria including mycobacterium tuberculosis. In this study, various conditions were optimized for the rapid and efficient labeling of rifampicin antibiotic labeled with Tc-99m for ultimate use in infection imaging. Radiochemical purities were checked by RTLC using methyl ethyl ketone, and normal saline on Whatman No.1 paper. The time, temperature, ligand concentration, stannous ion amount, pH were optimized in the radiolabeling process and the best conditions were room temperature, pH 7, 20 micrograms of stannous chloride for 1 mg of rifampicin solid and 20 mCi of freshly milked technetium-99m pertechnetate. The complex demonstrated satisfactory stability in the presence of human serum and final formulations for 6 hours.

Tokamak divertor plasma is characterized by variety of plasma parameters such as plasma density and temperature, as well as plasma composition and overcoming plasma dynamics processes. A model was surveyed for theoretical study of the interaction of hydrogen with dust surface and the results is applied to the formation of H2 molecule on the dust grain surfaces in the tokamak divertor plasma. In this model, by considering both physisorbed and chemisorbed sites on the grain surface, the adatoms on the surface migrate from one adsorb site to other adsorb site by thermal diffusion and form H2 on the dust grain surfaces. The H2 formation rate on the high temperature dust surfaces in the divertor plasma region has been found for a range of gas temperatures and densities.

A Russian design of Lead- cooled Fast Reactor (LFR) with a mixed uranium-plutonium nitride fuel is chosen as a case study. In order to demonstrate the inherent safety considered in this proposed design in the framework of Generation IV of nuclear reactors, a precise simulation of core has been attempted using MCNP lattice features. The material cross sections have been developed by NJOY & MAKXSF at different temperature levels. Meanwhile, certain static and dynamic parameters such as core effective multiplication factor (keff), group-wise and effective delayed neutron fractions are derived. Thermal reactivity feedbacks are calculated by changing the core composition and layout in the MCNP and inspecting its effect on keff. A complete systemic model comprising neutronic, thermal hydraulic (for hot channel) and feedbacks sub-systems has been developed. The power reactivity coefficient and reactivity margin (indicative of the maximum reactivity available to insert into the reactor core) are derived afterwards and it is demonstrated that the BREST reactor is equipped with inherent safety, and its reactivity margin stands well below the value of beff. The reactor, therefore, does not undergo prompt-criticality phenomena in available reactivity insertion accidents. Meanwhile, certain transient analyses are taken into account to verify the reactor intrinsic safety. Besides, a stability analysis through the formation of state transition matrix for the system describing equations and calculation of its eigenvalues which represent the system poles has been conducted. A set of poles with negative real parts stands for a dynamically stable system which is also a measure of the inherent safety.

The radioisotope of 123I (13.2 h) is widely used in nuclear medicine diagnosis studies using single photon emission computed tomography (SPECT). At present, it is mostly produced by proton irradiation of highly enriched 124Xe in a gas target and based on the decay chain of 123Cs→123Xe→123I. Achievement of high purity and high activity of 123I requires the characterization and the optimization of production conditions such as geometry of gas chamber and optimum range of the projectile particle energy. In this research work, for achieving the maximum purity and high activity, the excitation functions of 124Xe (p, 2n) 123Cs, 124Xe (p, pn) 123Xe and 124Xe (p, 2p) 123I reactions were calculated using five different nuclear models. The theoretical results were compared with the experimental obsetvations. By using the excitation functions, the optimum range of the production was selected. The Monte Carlo method indicated the beam transport situation in the target body and energy distribution of protons in the gas. For this purpose the calculations were carried out by using MCNPX and SRIM codes. Then, the target geometry was designed as a Frustum-shaped. Finally, by means of the MCNPX code, the 123I production yield was estimated. Good agreement between the simulated results and the theoretical yields, as well as the experimental yields was observed.

The effects of gamma irradiation doses on spore germination of Trichoderma harzianum and its effects on morphological variation and antagonistic capability of the mutants to control Rhizoctonia solani were evaluated. Spore suspension of Trichoderma has been gamma irradiated with 0, 50, 100, 150, 200, 250, 300, 350, 400 and 450 Gry in Nuclear Agricultural Research School (Nuclear Science and Technology Research Institute, Karaj). Gamma ray effects on mycelial growth were evaluated by irradiation with 0, 400, 800, 1200, 2000 and 2500 Gry. The results showed that the 450 Gry gamma radiations completely blocked the spore germination and 250 Gry was the optimum dose to induce mutation in Trichoderma. Furthermore, gamma irradiation could change the morphological characteristics such as colony shape and color, sporulation and mycelia growth rate. The dual culture test showed that the mutated isolates have statistically higher antagonistic capability against R.solani than their parent strain. According to these results, the bio-control capability of Trichoderma could be improved through the gamma radiation.

In order to reduce the problems due to use of chemical insecticides it is required to apply safe and proper methods to control insect pest. In this work, the combination effect of gamma radiation and Carum copticum C.B. Clarke essential oil against Trogoderma granarium Everts larvae, which is known as the major pest in the stored products, was investigated. Experiments were carried out at 27±1oC and 65±5% R.H. under the dark condition and three cases were represented. They are: 1) application of gamma radiation and essential oil simultaneausly, 2) irradiation followed by the essential oil, 3) the essential oil followed by the irradiation. The mortality was recorded 24h after the initial treatment. Doses among 700-1000 Gy of gamma radiation and 14.25, 20.88 and 35.97 ml of oil were used. The study showed that the combination of gamma radiation with C. copticum oil increased the larvae mortality compared with the control one, so that the combination of 900 and 1000 Gy with doses of essential oil (14.25, 20.88 and 35.97 ml) increased the mortality to 100% after 20 days, where as these gamma doses alone could control only 20% of larvae after 20 days. The best interaction was obtained when the fumigated larvae were exposed to the radiation. The results showed that irradiation and essential oils can be used as a successful control of the stored product pests.

The studied area is situated in the Central Iran structural zone. Uranim, thorioum and REEs (Rare Earth Elements) mineralizations are hydrothermal type and metasomatic related to intrusive areas. Recognition of a geochemical anomaly from background is a basic problem in geochemical exploration. There are different kinds of methods that assist to delineate geochemical anomalies from background, ranged from the simple statistical methods to complex fractal ones. The fractal models are applicable in this branch (geochemistry) because of using all data and considering their special distributions and their new effective usage of surface geological and geochemical studies. In Saghand area, REEs show a high positive correlation with radioactive elements (uranium and thorium). Recognition of REEs’ geochemical anomalies from background was achieved using the concentration- area (C-A) fractal model by lithogeochemical data (91 samples) in the study area. (we have analyzed 15 elements and provided Ce, Y, Dy, Gd and La elements’ maps in this paper). In this method, the log-log plots of REEs were generated and their theresholds and mineralization populations were identified. The map of lithogeochemical anomalies were subsequently drawn and eventually the promising areas were identified. Furthermore, high intensive REEs geochemical anomalies were discriminated in western, NW, central, and southern parts of the study area. The REEs moderate anomalies are located in the metasomatic unitis associated with epidote and chlorite alterations in the central part of the study area. The southern anomalies of the region are located on the border where the basic dykes associated with the epidotic alterations are between metasomatic units and microdioritic ones. High intensive anomalies which are situated in the west of the studied area occurred within the metasomatic, porphyry microdioritic, and acidic volcanic rocks associated with the epidote alterations. The combinations of the geochemical and geological maps were found indicating that the radioactive element mineralization was of the metasomatite type and metasomatism was more than amphibolization and albitization. The primary rocks contain pyroclastic, diabase, porphyry dacite and gabbro has affected metasomatism and the main rock types created in the area include amphibole metasomatite, amphibole-albit metasomatite, albite metasomatite, amphibole-quartz- feldspar metasomatite, amphibole-feldspar-epidote metasomatite and amphibole-biotite-talc-chlorite-epidote metasomatite. The REEs appear as a complex with the radioactive elements in U and Th minerals (uraninite and davidite).

Although in the mid- twentieth century, the international community and law accepted and approved freedom of trade among nations as a fundamental principle and to enact it implemented international mechanisms and although the right of all states to peaceful uses of nuclear technology and international community duty to global development of this technology were confirmed in various international instruments, imposing some limitations and exceptions to this principle in some international documents related to the export and import of nuclear materials and broad albeit apparently judicial interpretation of the advanced nuclear states of these conditions and exceptions, led the free flow of goods in international trade to face discriminatory restrictions in practice. This caused doubt and uncertainity regarding applicability of the principle of freedom of international trade in nuclear materials. The present article focuses on the study and evaluation of the legal system of international trade of nuclear materials and its constraints within the framework of the WTO, as well as the non-proliferation of nuclear weapons rule.

During the cold start-up, the reactor is in sub-critical state. Therefore, the external neutron source cannot be neglected. In this research paper, the analytical solution of neutron point kinetics equations with a group of delayed neutrons in the presence of the pulsed neutron source in a pressurized-water reactor with 235U as a fuel is presented. The analytical solution is based on the expansion of the neutron density in powers of the prompt neutrons generation time. The point kinetics equations with this method are solvable for step and ramp reactivity and lead to better results compared with other analytical works, but are not solvable for sinusoidal reactivity. So, the neutron density response to sinusoidal reactivity is analyzed by using the fixed point and Lyapunov exponents method.