m. johari

In the current research work, the alkaline precipitation method was used for the primary separation and purification of uranium in the solution which obtained from the dissolution of the evaporation pool scrap (C36) of the uranium processing plant. In this method, the effect of various parameters such as pH, temperature, stirring speed, aging time and seeding on the uranium precipitation yield as a sodium diuranate and the amount of impurities such as sodium and fluoride in the precipitate were evaluated. The results show that by increasing the pH of the solution up to 14, the separation yield increases up to 98.1%. Nonetheless, using the seeding method, the pH value is reduced to 12  and the separation efficiency increases to 99 %. Also, the results show that increasing the aging time and stirring speed increases the separation percentage and decreases the amount of sodium and fluoride impurities in the precipitation, while increasing the temperature leads to an increase in the separation percentage of uranium and impurities, too. In general, by applying the seeding process, pH adjustment up to 12, aging time of 12 hours, temperature of 50°C and stirring speed of 250 rpm, the best conditions for the primary uranium separation as a sodium diuranate with the minimum amount of major impurities in the precipitation were obtained.

Corrosion of steel bars in reinforcement concrete is the most important factor in the destruction of concrete structures. Till now, several protection methods for reducing the rate of corrosion of steel in reinforced concrete structures have been used, which corrosion inhibitors due to economical, easy to apply and efficiency, compared to other methods, faced with more attention. In this study, the effects of the simultaneous use of sodium nitrite and sodium-potassium tartrate inhibitors have been investigated. For this purpose, open circuit potential tests, electrochemical impedance spectroscopy and cyclic polarization were used in simulated concrete pore solution. This study aims to reduce the consumption of sodium nitrite due to environmental problems reported for it and also its destructive effects on the mechanical properties of concrete. Electrochemical impedance spectroscopy showed that the combination of these two inhibitors, improves the corrosion resistance by 91%. This rate is higher than the best performance of each of them, and finally, the synergistic parameter of 2/2 was calculated for this combination. According to the scanning electron microscopy images and the parameters obtained from the fitting of the Electrochemical impedance spectroscopy data, it seems that the simultaneous use of these two inhibitors at appropriate concentrations leads to the formation of a flat, uniform and chloride-resistant layer. Also, according to the results of the cyclic polarization test, the simultaneous use of these two inhibitors increases the pitting potential to 691 mV. Generally, it improves the resistance of steel specimens to pitting corrosion.

Corrosion of steel in concrete is the most important reason for the premature destruction of concrete structures. The use of corrosion inhibitors is a suitable way to control the corrosion of reinforcement in concrete. These chemicals are added in small amounts to the corrosive medium to reduce the rate of corrosion by affecting the rate of anodic, cathodic, or both reactions. In this paper, we investigate the corrosion inhibitory effects of disodium hydrogen phosphate, sodium molybdate, and sodium nitrite in simulated concrete pore solution in two concentrations of 1.8% and 3.5% NaCl. Hence according to the tests performed in simulator solution containing 1.8 wt.% NaCl salts, the nitrite, phosphate, and molybdate inhibitors added in 0.2, 0.0002, and 0.15 M, resulted in the efficiencies of 69, 59 and 81 percent, respectively. Also, in scanning electron microscopy micrographs, it was found that the use of these three inhibitors dramatically reduces the number and distance of surface pits compared to the control sample.

Mandibular second premolars are the third most frequent impacted. By evaluating the three-dimensional position of the impacted tooth and timely treatment, possible problems and damage to adjacent structures can be prevented. This study was designed to assess the position of Impacted Mandibular Second Premolar (MnP2) as well as the effect on adjacent structures using CBCT imaging due to the lack of adequate studies in this field.

This cross-sectional study was performed on 25 impacted mandibular second premolars. Two radiologists assessed and compared CBCT images to determine the following variables: unilateral/bilateral, position of the crown, root resorption of the adjacent permanent teeth, root dilaceration, depth of impaction, type of impaction, pathology incidence, residual primary tooth, position and distance to inferior alveolar nerve canal and the mental foramen.

In most cases, unilateral impaction was seen (19(76%), p=0.063). Crown position of most of MnP2 was displaced lingually (17(68%), p=0.324). Vertical and distoangular position of tooth were more common (12(48%) and 5(20%), p=0.922). Root resorption of the adjacent permanent teeth and dental pathologies did not occur in any of cases. Most of Mnp2 were categorized under the classification as mild (14(56%), p=0.270).

According to the results of the present study, it is unlikely that the MnP2 of young patients analyzed in this study would adversely affect adjacent structures.

While the benefits of cone-beam computed tomography (CBCT) are well known in maxillofacial imaging, the use of this modality is not risk-free. The aim of this study was to evaluate the exposure doses received by patients during maxillofacial imaging with CBCT. Entrance surface dose (ESD) was measured by using thermoluminescent dosimeters (TLDs) attached to the eyes lids, parotid glands and thyroid of 64 patients in two imaging centers (A and B). Phantom dosimetry was performed by a cylindrical poly-methyl methacrylate (PMMA) head-size phantom and an ionization chamber for different exposure parameters. NewTom VGi and Planmeca Promax 3D CBCT scanners were used at centers A and B, respectively. The mean ESD of the eyes, parotid glands and thyroid were 2.57, 2.33 and 0.28 mGy in center A, 0.35, 2.11 and 0.37 mGy in center B, respectively. ESD of the eyes revealed a significant difference in two centers; in center B, it was 86.4% lower than center A. In the phantom dosimetry, the measured doses of NewTom VGi were 2.63 and 2.08 mGy, respectively by changing field of view (FOV) size from 8×8 cm2 (height × diameter) to 6×6 cm2. For Planmeca Promax 3D, it ranged from 0.98 to 3.24 mGy depending on exposure parameters. There is a wide range of radiation doses dependent on the units, patients and selected scan parameters. Inappropriate selection of exposure settings, especially FOV size, can seriously increase patient dose.