مجله علوم و فنون هسته ای
سال سی‌ام شماره 1 (پیاپی 47، بهار 1388)

In this study, a pulse shape discriminator (PSD), incorporating zero-crossing method has been developed. The separate measurements with 241Am-Be and 252Cf sources undertaken by BC501A liquid have shown that the purposed and the common-used PSD’s are in good agreement. The improved characteristics of the presented PSD are FOM=1.36 at a threshold of 60keVee and 1.5µsec dead time which allows the count rates up to 50kHz.

Uranium as a natural radioactive heavy metal, widely disperses throughout the earth's crust. In many cases, the natural abundance has been re-distributed due to anthropogenic activities, resulting in radionuclide contamination in groundwater and surface soil. A pot experiment had been conducted in the Agricultural College Research Greenhouse, at the Ferdowsi University of Mashhad under the controlled condition. The effect of six levels of uranium (0, 50, 100, 250, 500 and 1000 mg U kg-1) on physiological characteristics and chlorophyll contents in sunflower and soy bean were studied in a completely randomized design as a factorial experiment with three replications. Plants were harvested after 40 days and before the reproductive stages. Root and stem length, root dry weight, stem dry weight, biomass and chlorophyll contents were determined. The shoot and root length, fresh and dry mass as well as leaf area and chlorophyll contents showed a significant negative correlation with the applied uranium concentrations. The influence on plant growth was also measured in terms of tolerance index TI and grade of growth inhibition GGI. The results showed that TI increased and GGI decreased with the applied uranium concentration. Biomass and tolerance of sunflower during the experiment on higher uranium concentrations showed that sun flower is more resistant against uranium toxicity.

In geochemical stream sediment surveys in Moghangegh Region in north west of Iran, sheet 1:50,000, 152 samples were collected and after the analyze and processing of data, it revealed that Yb, Sc, Ni, Li, Eu, Cd, Co, as contents in one sample is far higher than other samples. After detecting this sample as an outlier sample, the effect of this sample on multivariate statistical data processing for destructive effects of outlier sample in geochemical exploration was investigated. Pearson and Spearman correlation coefficient methods and cluster analysis were used for multivariate studies and the scatter plot of some elements together the regression profiles are given in case of 152 and 151 samples and the results are compared. After investigation of multivariate statistical data processing results, it was realized that results of existence of outlier samples may appear as the following relations between elements:- true relation between two elements, which have no outlier frequency in the outlier sample.
- false relation between two elements which one of them has outlier frequency in the outlier sample.
- complete false relation between two elements which both have outlier frequency in the outlier sample.

Ortho- tyrosine detection method can be used for detection of irradiated protein rich foods. Tyrosine isomers produced by gamma radiation of aqueous phenylalanine solutions at wide dose levels (0.1-50kGy) were examined to obtain basic information for o-tyrosine detection method of irradiated foods. Determination of tyrosines produced in aqueous phenylalanine solutions were carried out by high performance liquid chromatography and fluorescence detection. The detection limit of o-tyrosine was 0.01ppm and the linear range of calibration and the relative standard deviation of analysis was 50 ng and 4-13%, respectively. The amounts of the tyrosines increased with the irradiation level up to 10kGy and no further tyrosine formation was observed when the dose level was increased. At a constant dose level, the yield of tyrosines initially increased with the phenylalanine concentration, while with further increase of phenylalanine concentration no effect on increase of tyrosine yield was observed. When the dose rate was varying from 2.3kGy/h to 1.2kGy/h with a total amount of 10kGy in each case, there was no significant effect on tyrosine isomers formation was observed. Also the results showed that tyrosine yield was affected by temperature, pH and the presence of oxygen.

The radiation stability of polypropylene produced in Bandar Emam Petrochemical Co. and stabilized with two phenolic antioxidants (Irganox 1010, Irganox 1076) and two hindered amine light stabilizers, HALS, (Tinuvin 622, Tinuvin 770) have been investigated. The effectiveness of the stabilizers at 0.2% concentration on the polypropylene samples irradiated at 25 kGy has been followed for 6 months after irradiation. The buildup of carbonyl group and trends of the change in bend strength and MFI for the stabilized samples with Irganox 1076 and Tinuvin 622 show the post-irradiation embrittlement of these samples. The negligible change in carbonyl group, bend strength and MFI for the samples stabilized with Irganox 1010 and Tinuvin 770 indicated the better effectiveness of these two stabilizers.

Ceramics have been extensively used for gaseous molecular separation. In our present research, the procedure to fabricate membrane filters along with SEM studies for multi-layered structures are explained and the importance of high temperature and pressure are discussed in detail. The base material of the multi-layered filters base ceramic material was produced at high pressure of 1400oC, within a period of an hour. Meanwhile, the over layer was generated on the base material by Ni evaporation, using electron beam technique as well. Our studies indicated that the granular ceramics, as a base material, which was formed by sintering contains porosities and cavities due to the applied pressure. The SEM studies show, that the size of porosities ranges from tens to hundreds of microns. Our results are also discussed in terms of the importance of pressure and temperature in fabrication of these membranes.

Sodium fluoride is one of the most important adsorbents in enrichment facilities, where it is availabe in the form of powder and pellets. Linear and parabolic curve of the reaction between uranium hexafluoride and sodium fluoride, in the form of powder, in comparison with the parabolic curve of sodium fluoride in the form of pellets is shown that it is the best shape for the sodium fluoride adsorbents. But, it is impossible to determine these properties only by comparison of UF6 and NaF reaction kinetics and, selecting the shape and dimension requires the study of the effects of loading and pressure drop. In this paper, effects of adsorbents shape on pressure drop and capacity is studied. Based on these studies, it was realized that as the dimension of adsorbents decreases, the active surface area increases and cansequently, the final capacity of the adsorption decreases.

This study was performed with the aim of determination of dose calibrators’ accuracy in nuclear medicine centers. Thallium-201 radiopharmaceutical was used for comparison of dose calibrators with each other and with the reference. After the measurement which was carried out in 12 centers located in tehran and other cities, and according to the data obtained from the reference, it was concluded that dose calibrators in 10 centers are with positive and 2 centers with negative errors, as compared with the reference.

Strontium-89 is one of the most important radioisotopes used in nuclear medicine for therapy of bone pain caused by bone metastases. That is due to the beta radiation with sufficient energy for destroying metastatic sites in bone tissue. The routine application is ensured by introducing 89SrCl2 radiopharmaceutical and then injection of a specific dose in human vein, where it leads to reduction of bone pains. In this research, 89Sr was produced in the Tehran Research Reactor (TRR) for both natural Sr (includes 84Sr and 88Sr) and enriched Sr (includes 88Sr of %99 purity) for the comparison and preparation of 89SrCl2 radiopharmaceutical. Natural radioactivated Sr which produces gamma radiation was injected in mice and then based on gamma spectroscopy in different tissues, a calculation was made for the dose absorption rate, defined by %ID/g. Also, radioactivated enriched Sr-88 was injected in mice and the %ID/g was calculated due to distribution of the beta radiation in mice tissues. In our biodistribution we observed a rapid blood clearance followed by the high absorption of activity in bone tissues. These data have shown that the prepared compound is a well defined radiopharmaceutical for the bone pain palliation in metastatic lesions.

The spent fuel assemblies (FAs) of Bushehr Nuclear Power Plant are planed to be transported by TK-13 casks. Each spent fuel transportation cask holds 12 spent FAs and has a thick steel container to provide shielding. The calculations have been performed for FAs with burn ups of 60 MWd/kg and a 3-years cooling period. The ANSYS®10.0 general finite element analysis package was selected for this analysis, since it is an analytical tool, widely used for licensing of spent nuclear fuel casks. The selected model included all the significant heat transfer paths within the casks and between the casks and the external environment. The computational model was subjected to the thermal environment of the tunnel during the fire transient using boundary conditions derived from the results of the fire dynamics simulator computational fluid dynamics code. The model of cask constructed in ANSYS®10.0 consists of a detailed 3-D representation of a symmetric half cross section of the spent fuel transportation cask and a complete cross section of the surrounding tunnel wall. In this model, the cask is oriented horizontally within the tunnel. This orientation gives the cask''s outer surface the maximum exposure to the highest temperatures in the fire environment. This includes exposure from the tunnel surfaces by thermal radiation exchange and the flow of hot gases generated by the fire, which results in significant convection heat transfer to the package during the fire transient. The results of this evaluation strongly indicated that neither spent nuclear fuel particles nor fission products would be released from the spent fuel transportation cask. The internal temperature of TK-13 cask which was analyzed through the fire tunnel scenario did not reach the level that could result in rupturing of the fuel cladding.