مجله علوم و فنون هسته ای
سال سی و چهارم شماره 4 (پیاپی 66، زمستان 1392)

An innovative method has been used to calculate electron beam energy spectrum using depth-dose curve. The depth-dose distributions of the electron beam with different primary energies emerging from the electron accelerator were measured in water phantom after passing through a lead scatterer plate, using a computer-controlled plane-parallel chamber dosimetry system. The obtained depth-dose curves of the electrons were considered as the primary data to calculate the electron beam energy spectrum. Considering that the empirical depth-dose curve is a combination of the single-energy electron depth-dose curves, the electron energy spectrums were calculated via mathematical methods based on the superposition principle. The depth-dose curves for single-energy electrons were also calculated using the EGS4 computer code. The results for the energies of the electron beams were found to be 8, 12, and 18MeV.

The purpose of this research is to investigate the energy and the angular distribution of nitrogen ions in SBUMTPF1 plasma focus device (3.2 kJ, 25 kV, 10.4 µF), using a polycarbonate solid state nuclear track detector. In this experiment, the operational voltage of the device is 23kV and nitrogen gas, under 0.5 mbar pressure, is used as a functional gas. In order to detect the ions more clearly, a 200 and 500 micron pinhole is utilized. Various thicknesses of aluminum filter were coated on the films. Detectors were set at 21.5cm away from the top of the anode and the angle toward the anode’s top was set at zero degree in order to determine the energy distribution of nitrogen ions. Also, a polycarbonate film with 1200 nanometer aluminum filter was used for determining the angular distribution, where it was set 10 cm away from the anode’s top, positioned at 0, 15, 30, 45 and 60 degrees in angle toward the anode’s top. Detector films were irradiated by nitrogen ions. The range of nitrogen ions in aluminum was calculated by the use of SRIM code. In addition, the appropriate thickness of aluminum filters in a range between 1200 and 2630 nanometer were obtained by this inwestigate to collect data by means of polycarbonate detectors.

The biosorption characteristics of uranium(VI) on reference and indigenous strains of live A.niger were evaluated. The influences of pH (3.0-7.0), biomass concentration (0.05-0.5 g dry biomass /100mL), initial uranium concentration (10-500mg/L), and contact time(30-1440 minutes) were investigated. In order to determine the residual concentration of metal, inductive coupled plasma spectrometry was used. The results indicate that the maximum biosorption of U on reference and indigenous biomass occur at pH=5 as 82.30% and 74.19%, respectively. The biosorption equilibrium was established in 60 and 120 minutes for reference and indigenous biomasses, respectively. The maximum biosorption was observed at a concentration 0.2 g dry biomass/100 mL for both biomasses. The maximum biosorption capacity of U was developed at an initial concentration of uranium 500mg/L as 105 and 143.5 mgU/g dry biomass for reference and indigenous biomasses, respectively. The adsorption process of reference and indigenous live A.niger could be well-defined by Langmuir isotherm with R2 values of 0.9972 and 0.9979, respectively. The obtained results indicated that the reference strain of live A.niger is more efficient for biosorption of U from aqueous solution in comparison with indigenous strain.

Facilitated transport kinetics of uranium (VI) from a phosphoric acid medium into another phosphoric acid medium as a receiving phase through a bulk liquid membrane containing di-2-ethylhexyl phosphoric acid (HDEPA) as a carrier was studied. The influence of phosphoric acid concentration in source and receiving phases, carrier concentration, type of solvent, stirring speed and temperature were investigated. The kinetic parameters (ke, ks, tmax, Jmax) were calculated for the interfacial reactions, assuming two consecutive, irreversible first-order reactions. The activation energy values were calculated as 29.40 and 19.51 kJmol-1 for extraction and stripping, respectively. The values of the calculated activation energy indicated that the extraction process was controlled by the mixed regime (both kinetic and diffusion), and the stripping process was merely diffusionally controlled. In comparison with HDEPA optimized conditions, though with adding trioctyl-phosphine oxide into membrane phase as a synergic agent, the extraction rate remained approximately constant but the stripping rate diminished dramatically that led to the decrease of the transport kinetics.

The present work deals with successive uranium and thorium recovery from the sulfate leach liquor of the ore deposit of the 5th Anomaly of Saghand using liquid-liquid extraction technique, where trioctylamine (TOA) and di-(2-ethylhexyl) phosphoric acid (D2EHPA) were used. The solvent extraction of uranium by trioctylamine in kerosene was investigated using Taguchi method. The extraction parameters were pH, extractant concentration, contact time and aqueous/organic volume ratio. The optimum conditions were determined as the extractant concentration of 5%, aqueous/organic volume ratio of 1, pH=1.6 and the contact time of 3 minutes. Under these conditions, the uranium extraction percent was 98.7% in a single step extraction process. For a deeper investigation of the achieved results by Taguchi method, the effect of different parameters such as contact time, temperature, concentration of extractant, and pH were considered. Thorium extraction from uranium extraction raffinate was performed by D2EHPA 4% in kerosene at pH=1.5-2 in a three step extraction process. The kinetic studies showed that the extraction follows a second order  kinetics. The optimium conditions for the selective stripping (back extraction) of uranium and thorium from the loaded organic phases were obtained when 5.0 M nitric acid and 1 M sulfuric acide were used, respectively.

In this study nano-crystalline zeolite beta is synthesized with tetraethyl ammonium hydroxide as a template with the aim of separation of Uranium (VI) from radioactive waste, and characterized by XRD, IR, XRF and BET surface area measurements. Furthermore, ion-exchange properties of synthetic nano-crystalline zeolite beta were evaluated for batch system by calculating the percentage of uranium ions adsorption. The effects of variables such as initial concentration, pH and contact time between the exchanger and liquid phase, on the adsorption of the U(VI) ions were investigated and optimized. The results revealed that in the optimal conditions including the initial concentration of 80 ppm, pH=4, and contact time of 120 min, the percentage of U(VI) ions adsorbed by the synthesized zeolite beta was 94%.

The pressurizer component controls and maintains the pressure within the primary loop in Pressurized Water Reactor (PWR). It plays a vital role in the safe operation of PWRs. In this paper, the dynamic behavior of a pressurizer in transient condition is simulated. A numerical model based on three control volumes is considered to simulate the behavior of the pressurizer in transient condition. These three areas include the vapor region, saturated water in contact with vapor region and the region where the surged water is mixed with the water within the pressurizer. In the developed model, wall condensation, spray condensation, evaporation, bulk boiling and the energy absorption through the heater and heat transfer through the wall to ambient phenomena are taken into account. The mass, energy conservation with water-steam state equations are used to calculate the pressurizer pressure, water level and temperatures of each region. The presented model is developed as a software package so as the user can simulate all the available transient with a great ease. Specifically, by using the developed software, heater on/off, spray, in-surge, out-surge and opening of relief valve can be simulated by the user action or through predefined scenarios. The Massachusetts Institute of Technology (MIT) pressurizer test facility experimental data for in-surge, out-surge and out-surge after in-surge transients, are used to validate the developed model.

In this study, a simple method for the AUC powder preparation from uranyl fluoride solution, which is more effective for uranium recovery from AUC effluent is presented. At first, the uranium was precipitated in the form of ADU with more than 99.99 percent efficiency by ammonia solution. Then, through overflowing the solution, most of the fluoride ions were removed from the precipitated uranium. By adding ammonium carbonate solution to the ADU slurry, the AUC with stochiometry formula with high efficiency was prepared. The remained uranium in the AUC liquid waste was recovered by ADU precipitation in 99.99 percent. In this step, the uranium concentration in the final waste solution was decreased to less than 1ppm, where it is an important factor for enriched uranium. The ADU slurry was recycled to the next cycle of the AUC production. In this study, the NH4+ concentration, CO32-/UO22+ molar ratio and temperature effects were studied on the properties of the AUC powder and the precipitation efficiency. The results show that the NH4+ concentration is only effective on the fluoride separation and precipitation efficiency. The AUC precipitation efficiency depends on the uranium concentration in the ADU slurry. Also, the uranium recovery depends on the uranium concentration in the AUC waste. Decreasing the CO32-/UO22+ ratio to a minimum value caused the maximum particle size of the AUC crystals to be on an average value of 121 microns. The results of the XRD and SEM for the AUC powder are also presented.

Electromagnetic Isotopes Separator (EMIS) has been installed in Karaj since 1991 in order to separate isotopes of a wide range of elements. Iron is successfully separated. Iron element has four stable isotopes, 58Fe, 57Fe, 56Fe and 54Fe. The natural abundance of 54Fe is 5.8%. The 54Fe isotope is used for production of radioisotope 55Fe which in turn is used as an electron capture detector and in X-ray fluorescence. The copper pockets and graphite front plate were designed and fabricated for separating and collecting Fe isotopes. After the selection and preparation of charge material, the electrical parameter of ion source and electromagnet were recognized. The mass spectra of iron isotope were recorded. The deposited 54Fe isotope was extracted from copper pocket and purified by electrodeposition, solvent extraction and purification methods. Chemical and enrichment analyses of 54Fe isotope were made by ICP-AES and TIMS, respectively. The formation of 54Fe2O3 was confirmed by the X-ray diffraction.

A PC-Based gamma-ray spectrometer has been developed with communication capability through the USB port. A 12-bit pipelined Analog-To-Digital Converter (ADC) associated with a FPGA operating at 12MHz is employed for pulse height analysis from a built-in pulse amplifier. Data Acquisition via USB port is programmed in the FPGA. The USB transfer rate was 921600 bits per second. The software implemented in the Lab-View software environment for saving, analyzing and displaying data on PC in the energy range of 4096 channels was used. The overall system performance was tested using a Na(Tl) crystal coupled PMT scintillation detector, and gamma standard radioactive sources of Cs-137 and Co-60. The integral nonlinearity of ±0.45% was obtained by an experiment. Both low cost and compact size of the system as a result of design specification were also verified. A 7.6% energy resolution was adopted for Cs-137 out of 662keV. During the same experiment, values of 6.64% and 6.16% were determined with Co-60 source (in 1.17MeV and 1.32MeV energies).

An imaging detector system based on scintillation detectors is designed, fabricated, and optimized for using in diagnostic radiology, industrial radiography, nuclear medicine, and research domain. The X ray from a Siemens Stabilipan Orthovoltage (SSO) unit after passing through an object, which may be a living sample or an electronic device, produces a planar distribution of visible light on a Gd2O2S:Tb3+ (GOS), which is the image of the object under the examination. The image quality parameters, including the contrast and resolution were determined by the inpatient quality indicator (IQI) tests. The imaging practices were adopted for different X ray tube voltages (kV), and focal-spot surface distances (FSD). The data corresponding to the imaging quality parameters were subsequently analyzed and plotted by MATLAB and ORIGIN softwares. The results for the image quality parameters, that is, the contrast and resolution, for different X ray tube voltages were found to be fairly close to each other. Thus, the imaging system has the capability to be used for different X ray energies and radionuclides with relatively desired results. The study is considered to be an initiative for fabricating industrial fluoroscopy and radiation surveillance systems.

In this work, the bubble removing from lead silicate glasses containing 70% PbO in different time durations and temperature conditions is compared with that of the ordinary soda-lime glass. Batches of lead glass powders weighing 50gr inside alumina crucibles were heat treated at 900, 950, 1000, 1050 and 1100˚C for time durations of 15, 30 and 45 minutes. A sample of soda-lime glass was heat treated at 1400˚C for 5 hours and poured in a steel mold. The effect of viscosity and density of melt on the rate of bubble ascending inside lead silicate and soda-lime silicate glass melt are discussed. By using the data of the total density of glass (glass containing bubble), the density of glass without bubble and the mean bubble size measurements, the total volume of the bubble and the variation of the volume and the number of the bubbles at different time durations and temperatures were determined. The rate of bubble removing in lead silicate glass is affected by the thickness reduction of the bubbly layer on the surface of the melt, then the bubble number reduction rate of the bubbly layer at different time and temperatures was considered as the kinetics of bubble removing.