مجله علوم و فنون هسته ای
سال بیست و هشتم شماره 3 (پیاپی 41، پاییز 1386)

Quadrupole ion trap is widely used as an ion storage in gaseous phase and as mass spectrometer. In its classical approach, a sinusoidal voltage form is used to confine the ions in a small region. By using an impulsional voltage, on the other hand, it is possible to increase the mass spectrometer resolution so as to be applicable for separation of light isotopes. In this article we present the theoretical treatment based on the first and second ion stability region. The results show that the first stability region is more adaptable to the impulsional mode of ion trap operation.

In the last three decades, 99mTc-MDP and 99mTc-HEDP have been used as diagnostic radiopharmaceuticals for bone imaging agents. The radioisotope Department after many investigations decided to develop the synthesis of a biphosphonate derivative, named 1-hydroxy-ethylidene-1, 1-disodium phosphonate (HEDP). In this article, we discuss the method of synthesis, formulation, and labeling of lyophilised kit with 99mTc. The results show that our kit has a high radiochemical purity (>95%), according to the US pharmacopeia. In addition, the stability of lyophilised HEDP kit is more than one year at 4-8oC.

Zarigan Prospect Area is located at 50 km North of Bafgh, East of Yazd Province. This area is a part of central Iran intercontinental drift, formed during pre-Cambrian. Calc-alkaline magmatic process (500Ma) with felsic composition has brought about different types of metasomatism. Radioactive mineralized zone was associated with "Na-K-Fe-Si" rich hydrothermal fluid that intruded following the tectonic activities with E-W trend. Mineralization is related to albite, albite-epidote-Amphibole and silicified zones that emplaced in the margin of Diabasic Dykes trending E-W. The main host rock is felsic Tuff. The thickness of mineralization is between 0.3-2 meters, dipping 30-35ºN. Main minerals in the active zone are: Ti-magnetite, Davidite, pitchblend, and other radioactive minerals, quartz and some sulfide minerals such as pyrite (3-5%), which are found mainly as disseminated, irregular veinlets and dispersed lenses. Uranium and thorium grade varies between 50-2500 ppm and 50-5000ppm, respectively. Subsurface geological studies show that the activity is discontinued in zones and radiation is related to shallow to intermediate depths (40>m). The contents of Ce, Ti and Zr (Trace Els.) and Fe 2O 3 (major Oxide) are also high and notable in this system.

Up to now, various calculations have been done for evaluating fusion energy gain and time dependence of temperature of compressed pellets such as DT, D3He, DD, H11B and 3He3He in the absence of magnetic fields. Experimental results and their comparison with the results of simulations based on central spark ignition model and volume ignition model, prove the accuracy of our computational code. Industrial usage of fusion energy needs an increase in fusion gain and a reduction in driver energy. So that here, using volume ignition model for nuclear spin polarized pellets (in a magnetic field), the energy gain is calculated. The comparison between results associated with the polarized and non polarized fuel, shows that spin polarization is an effective method for reducing the initial needed energy for ignition (up to 35%) and increasing the fusion gain.

Trace amounts of cobalt-57 were separated from nickel and extracted into isopherone in the presence of thiocyanate as a complexing agent. The effect of various parameters on the separation yield was investigated. These include: concentration of the complexing agent, aqua and organic phases volume ratio and acidity of aqua phase. The extracted cobalt-57 was backextracted into concentrated hydrochloric acid and the effects of hydrochloric acid concentration and volume on backextraction yield were investigated. 4% (W/V) ammonium thiocyanate solution, pH=1.5-2 and lower organic to aqua volume ratio gives the highest separation yield. 99.57% backextraction yield was achieved for cobalt-57 through 5 steps of washing with 5 N HCl.

Free-air well-type ionization chambers are used in brachytherapy medical centers for measurement of brachytherapy source strengths. In this investigation, the HDR-33004 free-air well-type ionization chamber has been simulated using MCNP-4C computer code for several aluminum alloys as chamber wall material. The relative response (electric current) behavior of the simulated chamber for various source positions along the chamber central axis has been calculated and shows good agreement with measured values. We have also observed that the calculated and measured reference points are situated at the same positions. The results showed that the calculated electric current for unit source strength of 137Cs does not depend on the chamber wall aluminum alloy type, but for 57Co and 241Am sources, a strong dependency on the type of aluminum alloy as chamber wall material is observed. The presence of high atomic number elements such as zinc in some aluminum alloys resulted in higher response of the chamber. It is also found that for similar Al-7091 alloys the calculated and measured responses for 137Cs, 57Co and 241Am sources are in good agreement, showing that the alloy type of the chamber wall material would likely be an alloy similar to Al-7091. The results of this investigation can be applied for design of free-air well-type ionization chambers for low energy gamma sources.

Carbochlorination of ZrO2 is the main part of zirconium production process. In this research the effect of temperature and total gas flow rate on carbochlorination of ZrO2 in the presence of carbon black was investigated. The partial pressure of Cl2 in this study was kept at 0.3 atmosphere. The results showed that ZrO2 conversion is strongly affected by the temperature. It is also shown that at 1223 K, the process is affected by the gas flow rate. The activation energy of the process was 60kCal/mol and the chemical reaction on the oxide surface was the dominant controller of the reaction.

The Monte Carlo method was used to determine full energy efficiency of a high-purity germanium (HPGe) coaxial detector within an energy range of 53.2-2614 keV. Also, measurement was carried out for a standard Marinelli beaker of 600cm3, which was placed into the reference material of mixed gamma. The plot of the experimentally derived efficiency versus the incident gamma radiation energy showed variations at certain energies which is attributed to the detector’s characteristics. The results obtained by the Monte Carlo method and those of the experimental measurements resulted in a standard deviation of 2.3 to 7%. The method was also applied to determine self-absorption correction of the environmental radioactive materials which gave rise to a deviation of 3–12%.