مجله علوم و فنون هسته ای
سال بیست و هشتم شماره 2 (پیاپی 40، تابستان 1386)

Finding the distribution of elements in a given sample is very important in biology, microelectronics and geology. By using a microbeam and scanning the samples, we can obtain a great deal of information about the distribution of elements. After the installation of a microprobe system in the Van de Graff Laboratory, we started applying this system. In this paper, we report some preliminary results on the distribution of elements in archaeological, geological, microelectronic samples. The aim of this paper is to describe the capabilities of the microprobe system in material analysis.

Electron beams are widely used in radiation therapy. Since the nominal electron energy value is not quite meaningful for physics or dosimetry purposes in treatment planning, depth dose data for electron beams must be determined and used. The purpose of this study was to obtain the depth dose data for the 6 and 8 MeV electron beams of a NEPTUN 10PC linac and evaluating its beam characteristics using Monte Carlo method. The linac electron beams were modeled using the BEAMnrc code. The DOSXYZnrc code was also used for the simulation of RFA 300 water phantom. The central axis depth dose and the beam profiles were calculated for the beam energies at the 10×10 cm2 field size. The R100, Rq, R85, R50 and Rp parameters were extracted from the normalized depth-dose curves. The calculated results were compared with the experimental data, where the agreement between them was very good. Since different linacs from the same manufacturer and model usually have the same structures, it seems that it can be possible to model different linacs based on a particular one from the same manufacturer by defining their energy spectra and the beam quality indexes. In addition, using this method enables us to assess the characteristics of the electron beam at the exit of the linac and the effects of every part of the linacs head structure on the electron beams. It may also be possible to study and evaluate the final dose distribution.

In this research we have determined neutrons spectrum and the intensity that produced from thallium target bombardment. We have applied SRIM and ALICE computer codes to thallium target and its copper substrate for 145 mA of 28.5 MeV incident proton beam from cyclotron Cyclone30. Because of the energy degradation of protons while passing through the thallium target and its copper substrate, the average energy of protons in different depths has been calculated by using SRIM computer code. Then, by applying ALICE computer code for each sub-layer, the neutron production cross sections and their energy spectrum have been calculated to determine the total neutron intensity and spectrum. Using the calculated neutron intensity of 1.22´1013 n/s as the source, the equivalent dose rate at the distance 6 meters from the target has been calculated by MCNP computer code and the result has been compared with the measured value. The 201Pb activity has also been calculated as 13.5 Curies. The measured 201Pb activity by Curie meter CAPINTEC CRC-712 is 13.1 Ci which is in reasonable agreement with the calculated value, bearing in mind the uncertainties in the proposed models and the measurements.

Configuration of Tokamak plasma has a dominant effect on its parameters. In the calculation of transport, there are some transport coefficients and quantities, where the knowledge of their precise values, according to the system of equations, is essential to be realized. Tokamak has a toroidal configuration, in addition to classical effects, it is necessary to study the neoclassical effects due to the field curvature. The trapped particles in strong electromagnetic fields oscillate on banana-shaped orbits which in turn affect many other collisional transport parameters. Here, a precise estimation of trapped particles based on the standard equilibrium model for an elliptical shape of Tokamak plasma has been carried out using Lin-Liu model. It should be added that in this calculation, the profile of the averaged magnetic field on the flux surfaces has been derived using analytical integration and consideration of an elliptic shape for ellipticity function in the limit of large aspect ratio and zero shift of magnetic flux surfaces. Having the fraction of the trapped particles, by following the formulation and using an appropriate model in various collisional regimes, the neoclassical conductivity of plasma in Damavand Tokamak is obtained and the respective variations have been found. The presented results can exploit the computation of transport and other quantities of Damavand Tokamak.

The main substrate of myocardial metabolism is fatty acids which constitutes the principal agent for myocardial consumption and provides almost 60-80% of the energy utilized by the heart in the resting state. Evaluation of cardiac metabolism is important for the assessment of some of cardiac disorders such as Ischemic Heart disease (IHD), cardiomyopathy (functional disorders) and Hypertensive cardiac disorders. Today, almost in all of the developed countries, PET is the first step for diagnosis and assessment of cardiac metabolic disorders. It is, however, too expensive to be used in all centers and are not available in all countries. In this regards, 123-IPPA was introduced as a substitute of PET system for evaluation of cardiac function (metabolism) and it is a complementary method for other Para-clinical methods. We decided to have a preliminary study on IPPA and due to the lack of 123-I, we had to use 131-I. The labeling of IPPA by 131-I, purification and sterilization of 131-IPPA done by the Chemistry Group of Cyclotron Ward and the bio-kinetic and imaging of rat, mice (Laboratory Animals) were performed in the Nuclear Medicine Group. After injection of a proper dose of this radiotracer, the imaging was performed in an appropriate time. In our first images, there were intensive accumulation of tracer in animals' thyroid glands, though after the intake of Lugol solution, the thyroid did not appeare and we had a number of excellent images of animal heart that was the target organ.

In this research five levels of  Saffron Corm weights (6-8-10-12 and 14 grams) and five dose of gamma radiation (0-2.5-5-7.5 and 10 GY) were used. There were 25 treatments with 4 replication. The statistical analysis were conducted on petiole and stigma length on both the irradiated and the controlled. There were no significant difference at 5% level and weight of Saffron Corms and the irradiation does on the petiole and stigma length. The chromosomal studies on the root tip showed the chromosome abnormality in corm weight of 8 and 10 grams and the doses of 7.5 and 10 GY. It can be concluded that irradiation of more than10 GY will cause abnormality and stops the emergence of Saffron. The best does of irradiation was found to be 5-10 GY.

The quantitative evaluation of uranium content in the Khoshomi boreholes has been mainly carried out based on logging and XRF laboratory data. In order to determine the correlation between aforesaid data, composition and chemical analysis has been accomplished at 115 zones by considering 3.05 meter intervals that is equal to the length of each drilling rod. In this relation, 55 parts with the core recovery coefficient more than 90% were selected and the correlation between their uranium and thorium contents were studied to determine the amount of radiation resulted from thorium. In the next stage, the regression equation was obtained using two methods, i.e. correlation between the total count and the uranium content, and the thorium depleted radiation and the uranium content. Using the first method, the average estimation error is approximately zero. But, as the estimated error variance is relatively high, complementary information is required for a favorable mining design.

The accurate determination of molybdenum (Mo) in biological materials is of considerable importance in medical science because of the essential role played by this element in human metabolism. Molybdenum is a component of enzymes responsible for the initial stages of nitrogen, carbon and sulfur metabolism of plants, animals and humans. This element is usually determined by neutron activation analysis (NAA) in variety of samples, but direct measurement of low levels of molybdenum in biological samples by NAA is difficult. Recently instrumental analysis procedures such as atomic absorption spectrometry (AAS) have been used in clinical measurements for determination of many trace elements in the biological samples. These techniques are much simpler and cheaper than NAA. In this paper we are reporting a method of sample preparation for determining molybdenum by using graphite furnace atomic absorption spectrometry (GF-AAS). This method is the most readily available technique for determination of molybdenum at the ng/g level in biological samples. It can be used for the routine hospital laboratory determination of molybdenum and has appropriate sensitivity and simplicity. The best and reliable results for molybdenum analysis was achieved by digestion of nails in HNO3 2N and was determined in the range from 0.11 to 5.10 μg/g.