مجله علوم و فنون هسته ای
سال سی و چهارم شماره 2 (پیاپی 64، تابستان 1392)

: Removal of stable cesium and cesium-137 by living filamentous cells of Oscillatoria homogenea cyanobacterium from aqueous solution has been investigated. The removal levels of the stable cesium and cesium-137 were found to be 989ng Cs/mm3 biomass, and 2389 mBq 137Cs/mm3 biomass, respectively, after the contact time of 240 hours. The optimum pH for cesium uptake was 10±0.3. No significant change was observed at the pH values of 4, 6 and 8 for the cesium sorption by the cyanobacterium biomass. Increasing the cyanobacterium biomass caused more removal capacity. The maximum removal efficiency in the liquid culture containing 133 mg/L cesium and 20.53 mm3biomass/ml culturewas 5.75 mg/l. The removal efficiency were found to be 1.1% and 51.2% as the Cs-133 concentration, ranged beween 0.133 to 332.5 mg/l, respectively. At the 1200 Lux illumination, the maximum removal value was 1065 ng Cs/mm3 biomass, and in the presence of 332.5 mg/l cesium concentration (2.5 mmol/L), the sorption was obtained to be 4530 ng/mm3 biomass. The microprobe PIXE analysis and autoradiography technique were used to confirm the cesium sorption on the biomass. The sorption of the stable cesium and cesium-137 were fitted to Langmuir isotherm, and the model parameters were found to be qmax=854 ng Cs/mm3 biomass, 2272 mBq 137Cs/mm3 biomass, b=0.00011(R2=0.97), and b=0.000009 (R2=0.96), respectively.

Uranium is a radioactive element that occurs naturally in the earth’s crust. However, in some areas its natural abundance has been redistributed due to anthropogenic activities, where consequently results in high levels of contamination. In order to study the effect of mycorrhiza fungi and phosphorus on the uranium uptake by sunflower, a pot experiment is conducted under a controlled greenhouse condition. The experiment was carried out in a completely randomized design with three factors, including three species of arbuscular mycorrhizae (Glomus mosseae, Glomus intraradices, non-mycorrhizae), two levels of phosphorous (20 and 60 mg/kg), and one level of uranium (100 mg/kg). Plants were harvested after 60 days of experiment and dry weight of root and shoot as well as the uranium and phosphorus concentration in the shoot and root were determined. The results showed that mycorrhizae fungi increased the resistance of the plant against heavy metals. Also, mycorrhizae increased the uranium and phosphorous contents in the shoot and root of the sunflower plant. The dry weights of the shoot and root and also the uranium concentration in the shoot of the sunflower plant were significantly augmented by increasing phosphorus level. The results revealed that mycorrhiza symbiosis raised the uranium concentration in the root more than the shoot. Thus, it seems that arbuscular mycorrhiza has a potential for enhancing the phytostabilization of the sunflower plant.

Soil organic carbon (SOC) plays an important role in the global carbon cycle, and study of dynamics concerns the recent development of nuclear industry. Physical fractionation, radiocarbon dating and FTIR spectrometry methods are among the most important methods for determining carbon dynamics and thereby the magnitude of soil carbon response to land uses. In this study, methodologies of carbon dating and FTIR spectrometry were used to characterize impacts of land use on mean residence times and quality (functional groups) of soil organic carbon based on physical fractionation methods in three land uses including deciduous, coniferous forests and rangelands. The FTIR spectra showed that higher aromatic carbon proportion and its lower decay rate of organic matter in coniferous forest have caused more SOC content. Free and intra-aggregates particulate organic matters (POM) have been recognized as criterion indices for deciduous forest use. Compared to the other land uses, the higher aliphatic to aromatic carbon ratios were obtained in litter and intra-aggregates POM of deciduous forest. The highest14C age in both forest land uses (deciduous and coniferous) was measured in the Bhorizon, while in the rangeland occurred at the A horizon. Aromatic functional groups as well as 14C age are suitable parameters for homification processes.

In this study, a computer program is implemented to calculate the neutronic parameters of a multiplier system by Monte Carlo method. This program is able to perform the calculation of various parameters such as the effective multiplication factor, neutron flux distribution, and effective delayed neutrons of the system. This program calculates the prompt and the total multiplication factor of neutrons separately, then it can be used to calculate the effective fraction of delayed neutrons by the use of the eigenvalues and also the prompt method. The results obtained for the effective neutron multiplication factor and the neutron flux distribution are compared with the experimental measurements and the results of using MCNP4C code. In this approach a good agreement between them was obtained. The comparison between the obtained results for the effective fraction of delayed neutrons of the prompt method with those of the experimental measuremants and other applied methods showed that the prompt method is a suitable approach for the calculation of the effective fraction of delayed neutrons.

Recent dvances in nanotechnology have enabled us to accumulate high atomic-number nano-materials, such as gold nanoparticles (GNPs), in tumor cells selectively using different techniques and take the advantage of the dose enhancement factor resulting from the presence of such high-Z elements as the vicinity of cancerous cells as a radiosensitizer agent. In this research, the GNPs with an average diameter of 50nm were synthesized and conjugated with folic acid. Different concentrations of this nanoconjugate were incubated with MCF-7 cells for 24 hours and its cytotoxicity was investigated. The results showed that increasing the nanoconjugate concentration up to a critical amount, affects the cells viability. The radiosensitizing effect of the folate nanoconjugate, with a concentration of 50μg/mL, on the MCF-7 cells was assessed under 2Gy of x-ray radiation, generated by an orthhovoltage radiotherapy machine, at various energies of 120, 180, 200 kVp, using the MTT assay. Significant differences in the cell survival were noted among the groups exposed to x-ray radiation with and without the nanoconjugate. A maximum dose enhancement factor of 1.34±0.03 was obtained for the 180kVp X-ray beam. The findings enable us to decrease by one third of the prescribed dose while having the same level of damage to cancer cells. Also, this dose reduction results in lower exposure to the normal tissues located close to the target.

Bone metastasis is a major consequence of several cancers. The prostate, breast, lung cancers are mostly associated with the bone pain. Different radioisotopes are used for the bone pain palliation. 175Yb is proposed as a proper alternative to other radioisotopes due to its relatively long half-life (T1/2=4.18 days), maximum energy beta particle Eβ-=470 keV (86%), low abundance gamma emission, low cost, and easy production. In this study, 175Yb was obtained by thermal neutron bombardment of a natural 174Yb2O3 sample in the 5MW Tehran Research Reactor (TRR). The radionuclide purity of the 175Yb was ascertained by recording gamma ray spectra using a gamma spectrometer with a HPGe detector. Radiolabeling was completed in one hour by the addition of EDTMP at room temperature and pH=8-9. The quality control and biodistribution studies were carried out in normal wild-type rats. The radiochemical purity was determined by ITLC and the results were found to be higher than 99%. This study showed favorable biodistribution features of 175Yb-EDTMP which are indicating its significant accumulation in the bone. Also, it was observed that clearance of the activity from other organs accrued after 4 days. This research presents 175Yb-EDTMP as a suitable radiopharmaceutical with a proper half-life and low dose for the bone palliation of skeletal metastases.

The extraction and concentration of rare earths from leach liquor of apatite concentrate of central Iran were investigated using combined precipitation and solvent extraction methods. Precipitation was carried out to remove undesirable ions and solvent extraction method using tri-n-butyl-phosphate (TBP) as an extractant was employed to separate and concentrate rare earth elements. The XRD studies demonstrated that fluro-apatite, ancrite and calcite are the comprising minerals in the examined mica (apatite) and fluro-apatite is the predominant mineral. The amount of rare earth element-oxides including Y, Ce, La, Pr and Nd were determined by means of X-ray florescence (XRF) analysis. The other chemical composition of apatite consists of: SiO2, CaO, Fe2O3 and P2O5. First, acid leaching operation was carried out by using nitric acid. The analytical investigation of the obtained leach liquor indicated that interfering ions include: Fe(II), Mg(II), Ca(II), S(IV), P(V) and F(I). The precipitation studies confirmed that the process was rapid and highly efficient to remove the interfering ions without removing rare earth elements. The effect of different variables such as extractant concentration, nitric acide concentration, temperature, contact time and Vorg./Vaq. were investigated and the optimum conditions for separation of lanthanides by TBP were determined. Selective stripping of lanthanides from the loaded organic phase were studied using nitric acid. The separation of rare earths by TBP was observed to be significant and more than 90 percent of rare earth elements were extracted. The thermodynamic functions of lanthanides extraction process have been calculated.

The spacer grids in nuclear fuel assembly are one of the equipments that affect the fluid flow distribution with the creation of turbulence and driven fluid flow in a sub-channel. In the present paper, the fuel bundle in the VVER-440 nuclear reactor that contains 60 fuel rods and 4 spacer grids has been simulated and solved by a numerical method. Three turbulent models were used. The results showed that using spacer grids over the fuel bundle led to an increase in the heat transfer coefficients. However, these grids increase the pressure drop. The results of this research can be used to design and manufacture the fuel assembly and obtain the relevant thermo hydraulic parameters to optimize the heat transfer of fuel rods.

Vanadium is an expensive and practical metal in different industries, and in Iran, in particular uranium ore residues contain a considerable amount of this metal. In this investigation reductive dissolution of vanadium using two strains, acidithiobacillus ferrooxidans and acidithiobacillus thiooxidans, in two pulp densities, of 0.5 and 1g/l, were surveyed at 30˚C, and 180 rpm. Acidithiobacillus ferrooxidans adapted to the medium sooner than the acidithiobacillus thiooxidans and had a better result in dissolution of vanadium. In 0.5 and 1g/l, more than 90% of vanadium was disolved by acidithiobacillus ferrooxidans during 6 and 12 days, respectively and by acidithiobacillus thiooxidans in a period of 9 and 20 days, respectively. The experimental data were fitted to first and second order kinetic models, and it was observed that vanadium dissolution followed the second order kinetic model correctly.

The aim of this work is to introduce the application of a rotary kiln system to be used in enamel industry for the purpose of melting lead silicate glass. Due to low volume of lead silicate glass produces during a day or a year, and the necessity to spend a large capital investment for using customary glass melting furnaces, it was decided to apply a rotary kiln system for melting lead silicate glass. In order to be assured for the high corrosion and temperature resistance, alumina refractories were used as a refractory for the inner lining of the rotary kiln. The lead silicate glass after melting and mixing inside the kiln and fritting was grinded inside a ball mill with alumina lining and balls to a powder of mesh size finer than 75 micron. The melting, fritting and milling were repeated 5 times. The results showed that there was neither entered any impurity from the refractory particles nor observed any color and composition change due to entrance of aluminum element to the lead silicate glass melt. The homogenization of the glass composition and the removal of the bubble from the glass melt was carried out extremely well.