مجله علوم و فنون هسته ای
سال بیست و هشتم شماره 4 (پیاپی 42، زمستان 1386)

Thermoluminescence dosimeters are well known for their widespread applications in dosimetry specially neutron dosimetry. In low neutron fluences it is usual to use (n,α) reaction for direct measurement of neutron fluence, but in higher values, some gray filters are necessary. And also supralinearity because of the high absorbed dose makes the direct reading of TLDs difficult. After anealing of dosimeters the absorbed dose from the internal activity was used as a mass for neutron fluence. In this work thermal neutron fluence in the range between 1011 and 1013 n/cm2 in the reactor core of Tehran Research Reactor was measured using TLD-600 thermoluminescence dosimeters. The influence of irradiation-induced damage effect on the response of TLDs and their subsequent readings have been minimized. The measurements were made reproducible in this manner. The induced TL-light reader due to self-activity in TLD-600 dependens on the neutron fluence caused a conveniently measurable TL glow curve. The accumulated TL-light was measured after storage periods of 24, 48 and 72 hours. A short theoretical treatment is also presented at this work.

Baffles are used for decreasing bubbles diameter in order to increase the conversion rate along the bubbling fluidized bed reactors. The appearance of this phenomenon is due to bursting of the bubbles during the pass of bubbles from baffles. In this work, a computerized modeling and simulation have been performed in order to obtain a fundamental knowledge of the influence of the baffles on the bubble diameter and the specific mass transfer area. The height of the bed is 5m and its diameter is 0.3m. Paffles are located at 1 and 2m from the bottom of the bed. A two phase model together with a comprehensive fluid dynamical description of bubbling fluidized is presented. The effects of baffles and gas superficial velocity on the operating behavior of fluidized bed reactors are considered. The results are compared to the previously reported documents, and the experiments which have been carried out. MATLAB software is used in this simulation.

In this research, adsorption of molybdenum has been investigated by a new silica aerogel. This hydrophobic silica aerogel synthesized on the basis of TMOS (tetra methyl ortho silicate) precursor and in the presence of two co-precursors, tri fluoro propyl-tri methoxy silane and di-ethyl tri-methyl silyl phosphite. As the obtained results show, this aerogel is highly capable to uptake Mo in an optimum concentration of metal solution of about 10 ppm, the optimum pH about 4, contact time about 5 hours and the adsorbent dose about 3gr for 50ml of metal solution. The kinetics approaches show that the rate of this adsorption follows a first order reaction and the rate constant (Kad) is equal to 0.1248(h-1). The thermodynamic approaches have also been studied, and thereby the feasibility and the spontaneous nature of  Mo ions adsorption on aerogel have been demonstrated. A comparison between obtained results from silica aerogel and the activated carbon shows the more capability of the synthesized silica aerogel.

In spite of chickpea's use in Iran and its ability of being replaced to adjust the shortage of protein in dietary habits, yield production is very low. One of the main reasons for chickpea's low yield production is its sensitiveness to some diseases, pest and environmental stresses. Genetic variation in chickpea is very low, because of its self pollination. In breeding programs, genetic variation plays an essential role so that the induction of genetic variation in plant population is very important for the plant breeders. The induced mutation through different kinds of mutagenes is one of the important ways of genetic variation. In this research, first the sensitiveness of four cultivars (ILC.486, Philip86, Bivinich, Jam) were assessed to different gamma ray doses (100, 200, 300, 400 Gy). The results showed that with an increase in gamma ray dose, the growth rate of chickpea’s genotypes decreases. In this respect, the decrease of growth rate has a linear relationship with the gamma ray dose and it is independent from the genotypes. The root length is more sensitive to gamma ray doses than its shoot, and it was observed that at the low doses the root growth decreases, comparing to the shoot growth. On the other hand, in high doses of gamma ray growth abration (Ageotropism, Albinism and etc.) were observed. Some traits variation (such as leaf shape, leaf size, leaf color, Albinism, etc.) were seen in M2 generation, and finally to continue the project, three doses of gamma ray (150, 200, 250) were selected for the next year.

The pollution control is one of the major aims to a factory for preserving employee's health and outside environment. The best way to control the dust is to design machines in such a way that either producing the dust is prevented or the amount of produced dust which goes to the environment be less than a defined limit. If dust control is not possible, other ways such as blocking the production area, using localized air control system, and personal controls can be applied. In this work, an attempt was made to examine the quality of different disposable personal masks to be used in industry, especially in nuclear industries. To accomplish the purpose of the study, 21 samples were collected from 10 different companies. In order to choose the most appropriate mask, these masks were examined for their effectiveness with the atmospheric particle method. The quality factor was calculated by examining the pressure drop. This research indicated that there was a significant difference between the qualities of the examined masks. The lowest, average and highest quality factors for different masks, are about 0.002. 0.044 and 0.247, respectively.

Oxide coated cathodes are by far the most important thermionic emitter of electrons which are used in various electron tubes such as thyratrons. In this research, an oxide coated cathode, sintered with Ni-powder with cross section of 0.07cm2 has made and its electron emission parameters such as current density and the work function (Φ=1.62eV) have been measured.

87Y/87mSr generator is widely used in nuclear medicine. 87mSr(2.8h,Eγ=388keV) and the parent isotope 7Y(80.3h,Eγ=484keV) are used for skeletal scintigraphy and dosimetry modeling. Theoretical studies of cross section indicated that 88Sr(p.2n)87Y reaction in a cyclotron appears to be an attractive way for high production of 87Y. The aim of this study is to design and fabricate a suitable target for the above reaction. A software in C language has been written to calculate the products yields, and to determine the optimum energy of proton (21-27MeV) and the target thickness in order to get a maximum yield for 87Y and a minimum yield for the rest of products. An increase of yield from 0.41mCi/μA.h for Sr(NO3)2 target to 0.57mCi/μA.h for ClSr2 target has been achieved. This gain can be due to the following reasons:i) better heat transfer from the target to the cooling system (with optimizing the target holder),ii) higher melting point of target, iii) increase of Sr weight percent in the target, iv) more activity because of  keeping the target surface cool.

Based on a set of experiments, using a transversely exited (TE) oscillator-amplifier N2-laser system (OSC-AMP) with the AMP effective length of 31cm, measurements have been carried out for small signal gain, g0, and saturation energy density, Es, for different AMP gap separations. It was found that the gain-value depends on the AMP electrode gap separation, dAMP and thereby the corresponding gain coefficient dependency on the E/p, Te, and pd values are introduced. This experiment shows that in addition to laser excitation length dependency of the gain coefficient, the electrode gap-separation is also an important factor for determining the gain-value, where in the present system it is maximized for pdAMP~55 Torr.cm. In addition, it was found that, regardless of the type of lasers, and their geometrical configurations, the measured Es-parameter is linearly related to the output energy density, E0.