JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY
Year:2016 | Volume:- | Issue:78 |Papers Count:12

The direction and magnitude of the magnetization of a permanent magnet has some deviation from the desired value after the manufacturing. This paper describes the physical and mechanical designs and finally the manufacturing process of a the Helmholtz coil for the first time in Iran in order to measure the permanent magnets magnetization for using in a planar undulator. The Helmholtz coil calibration has been discussed by using a current source and Hall probe with the necessary precision. The final precision for an easy-axis magnetization measurement is 0. 03%, and accuracy is 0. 015%. 160 permanent magnet blocks have been measured by the Helmholtz coil. The measurement results of the magnetization components are presented and results are used in fabrication of the first undulator at the ILSF.

With the change of an ion trap geometrical shape, ring and end-cap electrodes, and also damping force effects, the first and second stability regions are studied in a stretched Paul ion trap. In this article, according to a new idea, we changed the trap geometry based on the change in distances between the ring electrode (2r˳ ) and end-cap electrodes (2z˳ ). For this purpose, the geometrical parameter n=(r˳ /z˳ )2 was introduced in our calculations. Also, for the damping effects, we entered a viscous damping factor (k) in the Mathieu equation. The set of differential equation governing the motion of the confined ion is considered, taking into account the effect of damping force and the ion trap geometry. The Mathieu type differential equations were solved using Runge-Kutta Verner fifth-order and sixth-order method (RKV56). Comparisons were made with the corresponding stability diagrams without considering the effects of damping force in an ideal ion trap 2 2 (r  2z ). The numerical results showed that, for a given ion trap mode i. e., rf only mode, the damping force and the trap geometry played important roles in the relocation of the stability diagrams. The first and second stability regions in the presence of the damping force, according to trap’ s geometry, are reported for the first time.

A whole body counter is used for in vivo measurement of body radioactivity to access the internal exposure of radiation workers, as well as, the internal exposure of the public. The chair-type WBC is more suitable than the other geometry for rapid monitoring in radiation accidents. In this study, a transportable in vivo monitoring system with the chair-type geometry has been designed, and evaluation of the counting efficiency has been performed to calibrate the system effectively. The counter incorporates Nal (Tl) detectors (5cm dia. ×5cm), housed in a collimator, and the chair is shielded using 2cm thick lead layers. For calculating the seat angle of the chair and collimator angle, a Bottle Mannkin Absorber (BOMAB) phantom model has been used. The counting efficiencies have been obtained by using Monte Carlo simulation and from the conventional calibration experiment. For the calibration experiment, a torso phantom containing a point source is used. The minimum detectable activity (MDA) for 137Cs for 10min counting interval is 448± 47 Bq. The results indicate that the calibration of the whole body counter by the MCNPX code can be substituted for the actual calibration. It is shown that, the Monte Carlo simulation is an inexpensive alternative method to obtain the counting efficiency of the chair type WBC for design and accurate calibration purposes.

The reuse of sludge in agriculture leads to the transfer of some pollutants into food chain, thus hazarding the public health. The pathogens, heavy metals and nutrients in the sewage sludge from two wastewater treatment plants in Tehran-Iran, Shahid Mahallati and Ekbatan, were investigated in three independent samplings. Moreover, the reduction of pathogens after irradiation by 10kGy gamma ray from 60Co was studied. The obtained results indicated that the heavy metals and nutrients in both of the wastewater treatment plants comply with Environmental Pollution Agency Standards and the pathogens counts reduced to the extent of the permitted level after irradiation. Viable Ascaris eggs in Ekbatan sludge was more than permitted level even after irradiation. According to the obtained data, just the sewage sludge of Shahid Mahallati treatment plant produced class A biosolids by irradiation which means that it can be applied to the agricultural lands, public contact sites and even home gardens. The odor of irradiated samples reduced as compared with the control ones. Vector attraction reduction processes must be conducted before use. The capability of the mentioned dose of gamma ray in converting the municipal sewage sludge into a sanitary fertilizer, depends on the microbial contamination level, specially the numbers of viable Ascaris eggs.

Measurement of cadmium ratio is one of the basic parameters in nuclear reactors. In this paper, the amount of cadmium ratio for the Esfahan Heavy Water Zero Power Reactor (EHWZPR) in two pitches of 18 and 20cm have been measured. For the cadmium ratio measurements Mn-Ni foils were used. The activity of the Mn-Ni foils were obtained by plastic scintillator and NaI(Tl) detectors for beta and gamma rays. Also, changes of the cadmium ratio in the axial direction of the reactor, asymptotic region or stable spectrum were obtained. The length of stable spectrum of the reactor increased to approximately 19cm, in pitch of 20 to 18, due to the reduced number of fuel rods and critical height of heavy water. To verify the measured values, the Esfahan Heavy Water Zero Power Reactor was simulated with the MCNPX-2. 6. 0 code. The results of simulation were in good agreement with those of the experiments.

Development of a qualified thermal-hydraulics and the severe accident model of nuclear power plants (NPPs) is of crucial importance in their design, optimization and safety evaluation. This is also the first step in the safety analysis of the IR-360 NPP for which its design is domestically in process. Without an approved and “ qualified" model, deterministic safety analysis (DSA) results are not reliable. In fact, the quality of the developed model should be assessed to ensure the reliability of the analysis results. This study attempts to develop a qualified MELCOR model for the IR-360 nuclear power plant in the SNAP nuclear analysis software. By selecting the appropriate nodalization of the problem and their proper connections, the most important thermo-hydraulics parameters such as pressure and temperature of the fluid, mass flow rate, direction and magnitude of the flow in the primary loop, etc are calculated. A comparison is made between the design parameters and calculated values to obtain the deviation of the model values from the design data. The calculated deviations shown to be below the acceptable limits, specified by the DSA practice including the suggestions of the International Atomic Energy Agency (IAEA). This confirms the qualification of the developed model for the safety analysis of the plant in the next steps.

Two radioisotopes of 18F (T1/2=109. 7 min, Iβ += 97%, Eβ += 0. 63 MeV), and 13N (T1/2=10min, Iβ +=100%, Eβ +=0. 96 MeV) decay almost completely via positron emission. Due to this characteristic, these radioisotopes are used in PET (positron emission tomography) camera for detection of cancer cells. In this article, after calculating the excitation function for nuclear reactions leading to the 18F, 18O (p, n) 18F, and 13N, 16O (p, α ) 13N formation using the ALICE-91 nuclear code and by a comparison of the results with the experimental data, the best range of energy to produce with a cyclotron accelerator and the amount of heat deposited to the target material, was determined. For the waste heat removal, a miniature heat exchanger was designed and manufactured. A thermal design of the heat exchanger by the Aspen HTFS+ software was created, and its mechanical plan sheet was drawn using the SolidWorks software. After the fabrication of the heat exchanger and recirculation liquid target located at the liquid target room, 13N was produced via pure water proton bombardment with 17. 5 MeV energies verifying the theoretical calculations.

Designing ideal radiopharmaceuticals for use as the bone pain palliatives requires the utilization of a moderate or low energy β-emitters with a stable carrier molecule. In this direction, cyclic polyaminophosphonic acids are known to form thermodynamically more stable and kinetically more inert complexes with lanthanides, compared to their acyclic analogs. In this study, DOTMP as the cyclic polyaminophosphonic acid and bone-seeking ligand, and 47Sc radioisotope as a low energy β-emitter with the maximum energies of 0. 600MeV and 0. 441MeV and the short half-life of 3. 47d were considered and the therapeutic potential of the bone seeking radiopharmaceutical 47Sc-DOTMP was assessed by measuring its skeletal uptake in the animal model. Because of the limited availability of 47Sc, this study was performed upon using 46Sc radioisotope which is chemically identical. 46Sc was produced with an activity of 2. 3 (85. 1 MBq) mCi by irradiation of natural 45Sc2O3 target at a thermal neutron flux of 3. 5×1013 n/cm2. s in 48h at the Tehran Research Reactor (TRR). 46Sc-DOTMP was prepared in radiochemical purity of about 90% in a chelant-to-metal ratio of 60: 1. The in-vitro stability of the complex was evaluated at room temperature for 48h. Then, the biodistribution studies of the complex in 5 groups of mice were carried out for 7d.

Magnetic nanoparticles modifdied with Cyanex 302 were used for the separation and preconcentration of Th(IV) and U(VI) from synthetic nitrate solutions. The capacity of magnetic nanoparticles (≈ 10 nm) coated with Cyanex 302 for simultaneous separation and preconcentration of thorium and uranium from the nitrate medium was studied by means of the batch method. The effects of analytical parameters, including the amount of Cyanex 302, pH, and initial metal concentration on the extractive behavior of metal ions were systematically studied. The results showed that the optimum weight ratio of Cyanex 302 to magnetite nanoparticles was 10% and the optimum pH of solution for the simultaneous extraction of Th(IV) and U(VI) was equal to 6. The maximal capacity of the magnetite nanoparticles modifdied with 10 w% Cyanex 302 was found to be 60 mg l-1 of thorium and uranium. The influences of the fission products [Cs(I), Sr(II)] and interfering ions, including Fe(III), Cr(III), Mg(II), Mn(II) and Al(III) were also investigated.

Polyvinyl alcohol (PVA) with the desired bio-properties and relatively low cost has attracted special interest to make hydrogels, especially with the wound dressing application. On the one hand, irradiation is an appropriate method to prepare hydrogels based on PVA. In this method, the irradiation conditions, especially the irradiation dose, influence significantly the physical properties and therefore affect the performance of the hydrogel. The main objective of this research was to investigate the effect of electron beam irradiation dose on the physical and thermal (crystallinity) properties of PVA hydrogels. The hydrogels were prepared by irradiation of the aqueous solution of PVA (7 wt. %) at different doses. The gel content, equilibrium swelling degree and dehydration behavior of the hydrogels were evaluated. The chemical structure changes of the PVA due to irradiation and thermal behavior of the dried PVA gels were probed respectively by FTIR and DCS experiments. In the wake of increasing the dose, the gel content of the hydrogel increased marginally, while its swelling decreased significantly. There was no obvious effect on the hydrogel dehydration by changing in the dose. The FTIR results showed that besides the crosslinking, the PVA chains degradation was also augmented with the dose. According to the DSC results, increasing the dose caused reduction of the crystallization and melt temperatures of the PVA and increment of its crystallinity.