JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY
Year:2011 | Volume:- | Issue:3 (57)|Papers Count:9

An accurate, precise, fast and ease as well as the ability for measurements in depth are the characteristics that are desirable in measuring soil moisture methods. To compare methods (time domain reflectometry and capacitance) with neutron scattering for soil water monitoring, an experiment was carried out in a randomized complete block (RCB) design (Split Split plot) on tomato with three replications on the experimental field of IAEA (Seibersdorf-Austria). The treatment instruments for the soil moisture monitoring (main factor) consist of neutron gauge, Diviner2000, time domain reflectometer (TDR) and an EnviroScan and different irrigation systems (first sub factor) consist of trickle and furrow irrigations and different depths of soil (second sub factor) consist of 0-20, 20-40 and 40-60 cm. The results showed that for the neutron gauge and TDR the amount of soil moisture in both of trickle and furrow irrigations were the same, but the significant differences were recorded in Diviner2000 and EnviroScan measurements. The results of this study showed that the neutron gauge is an acceptable and reliable means with the modern technology, with the precision of ±2mm in 450 mm soil water to a depth of 1.5 meter and can be considorelas the most practical method for measuring soil moisture profiles and irrigation planning program. The TDR method in most mineral soils, without the need for calibration, with an accuracy ±0.01m3m-3 has a good performance in soil moisture and electrical conductivity measurements. The Diviner2000 and EnviroScan are not well suitable for the above conditions for several reasons such as much higher soil moisture and a large error measurement and also its sensitivity to soil gap and to small change in the soil moisture in comparison with the neutron gauge and the TDR methods.

Geostatistical methods are applied for modeling the mineral deposits at the final stage of the detailed exploration. By applying the results of these models, the technical and economic feasibility studies are conducted for the deposits. The geostatistical modeling methods are usually consist of estimation and simulation methods. The estimation techniques, such as Kriging, construct spatial relation (geological continuation model) between data, by providing the best unique guesses for unknown features. However, when applying this technique for a grid of drill-holes over a deposit, an obvious discrepancy exists between the real geological features and the Kriging estimation map. Because of the limited number of sampled data applied for Kriging, it could not appear as the same as the real features. Also the spatial continuity estimated by the Kriging maps, are smoother than the real unknown features. On the other hand, the objective of simulation is to provide some functions or sets of variable values, to be compatible with the existing information. This means that the simulated values have an average and the variance similar to the raw data and may even be the same as the measurements. we studied the Anomaly No.3 of Narigan uranium mineral deposit, located in the central Iran region and applied the Kriging estimation and the sequential Gaussian simulation methods, and finally by comparing the results we concluded that the Kriging estimation method is more reliable for long term planning of a mine. Because of the reconstructing random structures, the results of the simulation methods indicate that they could also be applied for short term planning in mine exploitation.

This paper evaluates the functionality of a designed small phantom for determining the accuracy and performance of megavoltage radiotherapy machines through an external quality audit. The small phantom was designed to check the photon beams at the reference and some non-reference conditions on a linac at two radiotherapy centers in Tehran. LiF TLDs were used for experimental dosimetry. A standard phantom with an ionization chamber and the Monte Carlo code were used to calculate the conversion factor of the doses in the small phantom to the conventional condition. The result of this study showed that the dose conversion factors derived from the measurements made in the designed and standard phantoms are in good agreement with those calculated from the MCNPX simulations. At the reference condition, the amount of difference between the simulation and measurement were 0.5 at 6 and 18 MV. The differences for the 7cm×7cm field were 0.2% and 0.3% respectively, while for the 20cm×20cm field were 0.1% and 0.6%, respectively for the above energy. Using the designed phantom, two similar Varian linacs were checked at the reference conditions and amounts of their deviation between the planned and measured doses were estimated. The amount of variations of the phantom dose conversion factor with the field size indicates that the small designed phantom is not only appropriate for the small field sizes but also for the large ones. The results confirmed the functionality of the designed simple phantom with TLDs as an appropriate mailing system to carry out dosimetric intercomparison among different radiotherapy centers.

In this study a new simple but a very effective method is introduced for the beam modeling of the invariant part of a medical linear accelerator. In this method, instead of segmentation of scoring plane and analysis of phase space file, the mirror image of a virtual point source, energy and angular distributions and dependencies between them are derived, directly. Then, the method was used for the beam modeling of a 6MeV photon beam of the Siemens ONCOR Impression accelerator, where the TALLYX capability of MCNP4C was used. Consequently a multiple point source model with angular dependent photon energy spectra was obtained. Then, the percentage depth dose curves and the lateral dose distributions in water phantom were calculated using the present model for three field sizes including 4cm×4cm, 10cm×10cm and 40cm×40cm, and the results were compared to those of full Monte Carlo simulations. The results showed that the agreement between them the for all the field sizes are excellent. Benefits of this method as compared with the phase space file analysis method including the ease of application and the errors removal caused by the spatial segmentation of the phase space data.

Uranium as a radioactive element is 500 times more abundant than gold and is widespreaded over the earth’s crust. The toxicity of uranium is much higher than its radioactivity. The removal of uranium from industrial and nuclear wastes is therefore an essential task. In this research, Zeolite Y was first synthesized and copper-tetraporphyrine was encapsulated in it’s pores. The adsorbent was characterized by different techniques including FT-IR, TG and UV-Vis spectroscopy. The adsorption of the studied cation was investigated at different experimental conditions. The effect of pH, initial concentration, time and temperature on the adsorption process was studied and optimized. The results showed that the adsorbent is a good candidate for the removal of the studied cation.

In this paper, design and construction of an IECF device which produces continuous neutron flux by the inertial electrostatic confinement fusion is reported. The device is a stainless steel cylindrical chamber of 60cm in height and 60cm in diameter. Inside the chamber two concentric stainless steel-made spherical electrodes of 13.5 cm and 41 cm in diameter were installed. At a deutron gas pressure in the range of 10-3 to 10-2 mbar a condensed plasma during the electric discharge at the central part of two sphere was observed due to the D-D fusion reaction. By using a neutron track detector and a GM counter covered by indium foil, a neutron flux of more than 106 n/S were recorded. A neutron dose rate of 100 mSv/h by the use of LB6411 neutron dosimeter was also detected.

An electrostatic accelerator tube capable of accelerating proton, deuteron, alpha beam and heavier ions up to an energy of 150keV has been designed and constructed. This tube can be operated with a Cockroft-Walton type high voltage generator. The construction of the tube is important from two different standpoints. First, because it will initiate the use of low energy accelerators for both scientific and industrial development in country and also this step will lead the country toward accelerator design technology, an issue which has been severely overlooked for the past few decades. The present accelerator tube consists of 11 different electrodes forming 3 cylindrical lenses, i.e., extractor lens, focusing lens and cooling lens. An accelerator column which includes 7 collimating lenses follows the cooling lens. The tube can accelerate 2H+ up to an energy of 150 keV. The accelerator column was successfully tested for the high vacuum and the voltage up to 150 kV. A radio frequency type ion source was used to check the performance of the tube. Measurements demonstrated that a beam current close to 850 mA can be readily obtained in the present system.

This paper deals a with the study of an innovative method for processing the Oman placer ores by alkaline leaching in ball mill autoclaves, where grinding and leaching of the refractory minerals take place simultaneously. This was followed by the selective separation of thorium and uranium from lanthanides by autoclave leaching of the hydroxide cake with ammonium carbonate-bicarbonate solutions. The introduced method is based on the fact that thorium and uranium form soluble carbonate complexes with ammonium carbonate, while lanthanides form sparingly soluble double carbonates. It was found that a complete alkaline leaching of Oman placer ores (98.0%) was attained at 150 and 175oC within 2.5 and 2h, respectively. Oman placer ores leaching was intensified and accelerated in a ball mill autoclaves as a result of the grinding action of steel balls, removal of the hydroxide layer covering ores grains and the continuous contact of fresh ore grains with alkaline solution. The study of selective carbonate processing of hydroxide cake with ammonium carbonate-bicarbonate solutions on autoclave under pressure revealed that the complete thorium recovery (97.5%) with uranium recovery (90.8%) and their separation from the lanthanides were attained at 70-80oC during 1-2h. The extraction of lanthanides in carbonate solution was low and did not exceed 4.6%.