مجله علوم و فنون هسته ای
سال بیست و نهم شماره 1 (پیاپی 43، بهار 1387)

The Ion Beam Techniques have opened a new window to study crystal structures and imperfections of crystals. In this paper, we try to briefly describe concepts and applications of
RBS-Channeling to determine crystal parameters and disorders. Some experimental results of the analysis of semiconductor materials are presented in this paper, which has been obtained by means of
RBS-Channeling technique.

The effects of gamma radiation on Mozafati date were evaluated in order to find microbial and chemical changes. For this purpose, the date samples were stored at different temperatures, 25°C (room temperature), 4°C (refrigerator) and -18°C (freezer) for a period of 6 months. At each temperature, 4 samples were considered as a control (unirradiated) and three others as irradiated with doses of 0.5, 1.0 and 2.5 kGy by the use of gamma irradiation. Every month, the samples, at each condition, were checked to detect the total microbial, mold and yeast contaminations. The same date samples were also analyzed to chemical and quality controls (sugar and moisture). Finally, the unirradiated samples were compared with the irradiated ones. It was concluded that the proper condition to decrease microbial contaminations and chemical changes, and to increase the shelf-life and stabilize quality of the Mazafati date is the dose rate of 0.5 kGy at 4°C temperature.

The objective of this investigation was to determine the potentials of some indigenous fluorescent Pseudomonads for siderophore production and their effects on 65Zn absorption in 2005. For this purpose, 201 strains of Pseudomonas putida, P. fluorescens, and P. aeruginosa were isolated from different locations representing rhizosphere of wheat (Triticum aestivum L.). The potentials of these strains for siderophore production were evaluated by chrome azorel-S assay (CAS blue agar) through color change. High siderophore producing super-strains were selected for the extraction of siderophores. These isolates were grown in SSM (standard succinate medium) for 72 hrs at 28C. The bacterial cells were removed by centrifugation (10000 g for 20 minutes) and the supernatant was filtered through filter membrane (0.22 μ) and used as the source of siderophore source. The evaluations of Zn uptake and translocation were carried out with the complexes of bacterial siderophores and 65Zn compared with the standard siderophore Desferrioxamine in a randomized complete block design with three replications. This experiment was conducted on two wheat genotypes different in Zn-efficiency under hydroponic condition. The results revealed that among the three most effective siderophores producing strains considered, the P. putida produced a siderophore complex that showed efficiencies of 83% compared with the standard siderophore (DFOB) in the uptake of Zn and was statistically in the same group as the control. The effect of bacterial siderophores in the uptake of labeled 65Zn by wheat was significant, indicating that the chemical structures of the siderophores from different strains were different. The effects of wheat variety on 65Zn translocation to shoots was also significant, where the efficient Tabasi variety contained 46% more Zn in shoots than the inefficient Yavarous variety. It was concluded that the siderophore complex from P. putida was the most effective in translocation Zn to shoots, particularly in efficient Tabasi genotype. Siderophore effectiveness in Zn availability decreased in the order of Sid-DFOB> Sid-P. putida>Sid-P. fluorescens> Sid-P. aeruginosa. Due to the availability of P. putida in absorbing Zn, the siderophores of this group of bacteria can be named as zincophore.

In this study a mathematical model is developed in order to simulate fluorination reaction of uranium dioxide leading to produce uranium hexafluoride. The model considers homogeneous reaction for intermediate solid and heterogeneous one for unreacted shrinking core. Also, this study tries to clearly show the shortcoming of those foregoing models that take surface reactions for both solids. In fact, one may not trust the accuracy of those models due to ignoring the importance of the diffusion phenomena into the intermediate solid and taking place the reaction within it. On the other hand, by neglecting the undeniable effects of operating conditions, including temperature and particle size on gas concentration distrbution and reaction rates may introduce large deviations. For this mentioned purposes, the governing equations are derived on the basis of the mass conservation law and have been solved numerically. Besides, for the first time, some dimensionless equations and groups are introduced to predict the reaction rates and the amount of the main and the intermediate products for using numerical procedure. Comparing the results with the corresponding experimental ones represents the desirable accuracy of the model. After validation of the model, the effect of some operational variables such as temperature and initial particle size have been investigated on the reaction rates and the conversions.

Characterization studies and determination of liberation degree are first stages of mineral processing. These studies are very important for determination of optimum comminution conditions, selection of preseparation process and determination of suitable processing methods. Khoshoomi mine with the average uranium grade of 1540ppm, is located at 150km northeast of Yazd. The characterization studies of this ore are made by XRD method and microscopic study, also degree of liberation studies are made by microscopic section. These studies are done by three powder samples, twelve thin sections and twelve polished sections. The major minerals such as Feldspar (Albite), Plagioclase (Orthoclase), Biotite, Chlorite, Carbonate and minor minerals such as Sphen, Zrconium, Actinolite, Tremolite, Pitchblende and Betafite were identified based on the results of these studies. Accordingly, by microscopic studies and heavy media method, the liberation degree of Orthoclase, Albite, Biotite and Uranium minerals were determined as 320, 290, 190 and 110 micron, respectively.

The investigation of β- particle interaction with matter has many applications in nuclear industrial and medical science. In this work, we have impose different loads on Al-Mg-Zn alloy and Al metal sheets with different thickness to investigate the effect of elastic stress on the absorption coefficient of β- particles of 90Sr. Also, we have modulated and analyzed the loads on specimens, using ANSYS9 program to determine the distribution of stress within the specimens. The results show a valuable increase of µ -value due to loading the specimens by certain amounts of stress, where the µ- value decreases as the stress on the samples increases.

In this paper, production of  high grade pure graphite in Bonab Research Center is reported. Firstly, we will explain the various graphite production process and the results of crystal lattice analysis such as XRD, density and chemical analysis are proposed. The density of manufactured sample is 1.86 g/cm3 which makes it suitable for many high sensitive technical applications. This is the highest grade purity that has been achieved in Iran. The process of manufacturing and the structural diagnosis of the prepared graphite is explained.

In this project, the activity concentration of some radionuclides in rice samples, collected from Guilan province have been analyzed and the results have been compared with rice samples imported from other countries. For this purpose, sixteen types of rice samples from different region of Guilan and four imported rice samples have been collected. The collected samples have been analyzed in order to determine the activity concentration of number of radionuclides such as 40K, 226Ra, 232Th and 137Cs. A gamma spectroscopy system with a high purity germanium detector (HPGe) has been used for the radioactivity measurement. The highest activity concentration in the rice samples belongs to potassium-40. The mean activity of 40K, 220Ra, 232Th and 137Cs were (30.23±5.51), (3.30±1.75)10-2, (3.78±1.65)10-2 and (2.65±0.99)10-2 Bq.Kg-1, respectively. It can be concluded that all the activity concentrations are comparable with the values that have been, imported for other countries.