مجله علوم و فنون هسته ای
سال چهل و دوم شماره 3 (پیاپی 97، پاییز 1400)

The present work measured the sign and the amount of nonlinear optical absorption coefficient and nonlinear refractive index of gold nanoparticles by Z-scan method. The Ti: sapphire laser is used in two modes: continuous wave and pulsed with 60 fs duration and a repetition rate of 80 MHz at the wavelength of 800 nm, with an average power of 28 mW. Gold nanoparticles were obtained by the laser ablation method with 20 ns pulses and a repetition rate of 10 Hz in SDS solution. Due to using femtosecond laser pulses with a high repetition rate, thermal and electronic nonlinear effects appeared. The results were compared with a continuous wave Z-scan at the same wavelength and exposure power to eliminate the cumulative thermal effect and separate the electronic and thermal nonlinear coefficients. The electronic and thermal nonlinear absorption coefficients were obtained 15×10-5 and 125×10-5cm.W-1, respectively. Kerr de-focusing effect occurred in both electronic and thermal nonlinearity, and the nonlinear electronic and the thermal refractions were calculated -41×10-9 and -34×10-9cm2W-1, respectively. The experiments show that the nonlinear coefficients of the sample prepared in this research are larger than the values obtained for the samples made by the chemical method.

Among the four stable isotopes of sulfur, the heaviest isotope, 36S, has found many applications in radioisotope production and neutron activation. In the present work, due to the very low natural abundance of 36S, the single withdrawal cascades are used to separate this isotope. The concentration distribution equations in the transient state are separated using the Laasonen method and linearized by the q iteration method to simulate the cascade. The code is validated using existing experimental results. To separate the 36S isotope to a high concentration of 90% by a fixed number of centrifuge machines, different arrangements of the square single withdrawal cascades, the feed stage location, and the feed flow rate were investigated. In the arrangement with 15 stages and eight centrifuge machines at each stage, the concentration of 36S in the reservoir reaches 95% after 1460 hours. The results showed that reducing the feed flow of the cascade and increasing the distance of the feed stage from the reservoir leads to an increment in the concentration of 36S in the reservoir.

In this study, flat membranes containing neat polyethersulfone and the mixed matrix membranes containing polyethersulfone and nanoparticles such as titanium dioxide(TiO2) and functionalized multi-walled carbonnanotubes (fMWCNTs) were fabricated by wet phase inversion. And the boron ions' rejection and permeat flux behavior of these prepared membranes were evaluated and compared using the nanofiltration process. The hydrophilic properties of the prepared membranes and their structure were evaluated by measuring the contact angle and the scanning electron microscopy method, respectively. To optimize the amount of boron ion’s rejection percentage and permeate flux on the neat polyethersulfone membrane, the operational parameters such as the weight percentage of polyethersulfone, pH, time, pressure, and boric acid concentration were investigated. Finally, the performance of mixed matrix membranes containing different percentages of nanoparticles was evaluated under these optimal conditions. The results showed that at optimal conditions (pressure=12 bar, polyethersulfone=20% (W/W), concentration of boric acid=20 ppm, time= 30 minutes, and pH=12), all the prepared mixed matrix membranes have higher boron ion rejection percentage and permeate flux than the neat polyethersulfone. The mixed matrix membrane containing fMWCNTs (0.7%wt) has the highest boron ion rejection percentage (95/79%).

A Polyvinyl chloride (PVC)-based polymer inclusion membrane (PIM) containing alamine336 as the extractant and Polyoxyethylene alkyl ether (POE) as the plasticizer was used for the Transport of uranium from sulfate solution. The effects of extractant and plasticizer concentration in the membrane, sulfuric acid concentration in the feed phase, stripping agent type, and concentration were investigated. The maximum flux of 1.82×10-7 mol/m2s was obtained using a PIM consisting of 40 wt.% alamine336, 23.21 wt.% POE and 36.79 wt.% PVC, 0.1 M sulfuric acid in the feed phase, and 0.5 M (NH4)2CO3 as the stripping phase. The effect of the initial concentration of uranium in the feed phase on uranium transport was also studied. The results show that in the studied range of uranium concentration, the Transport of uranium through the membrane was controlled by diffusion of uranyl ions through the feed phase mass transfer layer. The prepared PIM showed appropriate stability for the Transport of uranium for five consecutive experiments.

In the present work, we have simulated the collision of dust nanoparticles with graphite wall using LAMMPS code, based on the molecular dynamics method. Dust particles have different shapes and sizes depending on their production mechanism in Tokamaks. In this work, two types of dust grains have been considered: a spherical tungsten nanoparticle and a graphite nanoparticle with an oblate geometry that collides with a graphite wall. In the fusion device, ions, hydrogen atoms, and molecules collide with the dust grain and create stochastic torques, leading to minor variations in the angular momentum of the grain. Therefore, in the simulations, the dust rotation around its symmetry axis has also been considered in addition to the transfer velocity. For such nanoparticles, the threshold speed of nanoparticles that leads to surface damage has been estimated. The results show that, unlike tungsten nanoparticles, graphite grains do not play a significant role in the degradation of the graphite surfaces. Still, due to the speed of the collision, they may either stick to the surface or be damaged and return to the environment.

The Holmium-166 radionuclide is one of the most effective radionuclides used to treat bone marrow cancer and rheumatoid arthritis. Among the recommended radionuclides used in radiation synovectomy, 166Ho has got much attention due to suitable decay properties such as short half-life, its high beta energy, gamma-ray emission with suitable energy for nuclear imaging, and the possibility of large-scale production in medium flux reactor. One method to deliver 166Ho to the target tissue is via the 166Dy/166Ho-Chitosan in vivo generator. Compared with other similar radiopharmaceuticals, using the in vivo generator to deliver 166Ho, causes minimal non-target tissue exposure and increased absorbed dose in the target tissue. In this work, the absorbed dose of 166Dy/166Ho-Chitosan radio-complex for radio-synovectomy purposes was calculated by GEANT4 and MCNPX. The obtained results were compared with each other. In addition, the dosimetry results of the mentioned radio-complex have been compared with the common radio complexes used for radio-synovectomy.

In the present work, the propagation of nonlinear ion-acoustic waves is studied in a collisional plasma with superthermal electrons with a Kappa distribution function. Considering the basic set of fluid equations and the ion-neutral collisions, a modified nonlinear Korteweg-de Vries (K-dV) equation is derived by using the reductive perturbation method. It was found that only compressive ion-acoustic solitary waves can be propagated in this model. Also, the numerical results show that the ion-neutral collisions have significant effects on solitary wave structures. In other words, the amplitude (width) of the ion-acoustic solitons decreases (increases) with the increasing of the ion-neutral collision frequency. Moreover, the effects of the spectral index of superthermal electrons and ion temperature on the ion-acoustic solitons are also studied in the present plasma model.

In the present work, the X ray dose and hard X-ray spectrum corresponding to a 2.5 kJ plasma focus device was investigated. The X-ray dose using Argon gas at a pressure of 0.8 mbar and a distance of 23 cm from the top of anode was 0.8 mSv per shot. Using the ORNL phantom simulated based on the realistic human body, X-ray absorption dose was computed for soft tissue organs at certain distances from the device. The maximum absorbed dose was related to the distance of 30 cm for the testis in the male phantom (2.0890×10-14 mGy), and for the bladder and contents in the female phantom (2.6613×10-15 mGy). In addition, at the distance of 230 cm, the maximum absorbed dose was in the testis in the male phantom (3.5601×10-16 mGy) and in the skin for the female phantom (1.1004×10-16 mGy).

Recently,the use of fiber-reinforced polymers has become widely used in various industries. Carbon fiber reinforced polymers (CFRP) are widely used in the aerospace, nuclear, renewable energy, architecture, and marine industries. The complexity of the manufacturing process of these parts is always associated with the formation of various types of manufacturing defects. The existence of non-homogeneous structure in these parts has faced several limitations in the use of classical NDT methods in the inspection process. The active thermography method using infrared waves is today considered as one of the proposed methods in the inspection of composites. In the present work, samples with flat sheet geometry and curve sheet geometry of carbon fiber-reinforced polymer were tested using a pulse technique. Several different types of defects with different dimensions were manually created in these parts and inspection was performed using the thermography method. The results have shown that the use of radiant thermal stimulation with the transmission technique can well reveal the internal defects of the samples. The presence of different thermal conductivity of needle-shaped metal defects with 0.2 mm diameter, foreign particles with 2 mm diameter, and 10×10 mm2 delamination led to the appearance of these defects in flat and curved samples.

In the present study, high-density polyethylene (HDPE)/hexagonal boron nitride (hBN) and HDPE/Boron nitride nanosheets (BNNSs) nanocomposites with different contents were fabricated using the melt mixing method. The morphology, properties, and mechanical and thermal performance of composites and nanocomposites containing boron nitride were investigated. Also, the neutron shielding performance of the designed composites was investigated using the thermal column of the Tehran Research Reactor and foil activation method. The results were compared with those of using pure HDPE. HDPE/BNNSs nanocomposites have shown higher modulus and tensile strength, higher thermal stability, and better neutron shielding performance than HDPE/hBN. The results showed that by reaching hBN content to 0.5 wt. %, the neutron shielding of the composite was improved by 25% compared with the pure HDPE. However, there is a 43% increase in neutron absorption by nanocomposites compared with HDPE. The result of this work is expected to cause a natural synergy between applied nanocomposite and neutron shields and lead to the commercial production of Leigh-weight, inexpensive, and effective neutron-shield nanocomposites.

HWRR element is an instrumented fuel assembly constructed based on JCPOA conceptual design parameters for Arak reactor. The in-core experiments of the fuel are carried out in TRR core to evaluate neutronic and thermal-hydraulic parameters using an experimental facility called Open Loop Test Facility (OLTF). Safety analysis of the OLTF anticipated incidents is one of the necessary steps before its implementation. Therefore, three severe anticipated accident scenarios have been simulated, including two LOFA scenarios and the instant post SCRAM cooling by natural circulation. The neutronic calculation has been carried out by MCNPX code to determine fuel rods power and thermal-hydraulic analysis using CFD method. The analysis results show that the clad surface temperature violates coolant saturation temperature and void will arise in both LOFA scenarios. However, both clad and fuel temperatures keep significant margins to their design criteria and fuel rod integrity would be retained completely. The results also show that the coolant temperature remains lower than saturation temperature in the case of decay heat removing via natural cooling scenario.

In this study, the influence of grafting 198Au radioisotope on functionalized silica nanoparticles with a the biodistribution of this radioisotope compare to pure gold nanoparticles, was investigated. The Au radioisotope was prepared using neutronic bombardment of a highly pure metallic gold. The prepared radioisotope was coated on silica through an interface ligand. The biodistribution suggested that the hydrophilicity of the 198Au@MCM-41 nanosilica compare to pure gold nanoparticles was higher. Through the SPECT images and %ID/g measurement, it was found that the excretion of radiotracer from the body compare to pure gold nanoparticles became faster. The Au@MCM-41 nanocomposite could potentially be used in diagnosis and therapy of cancer.

Tc-99m is the most important nuclear medicine radioisotope produced from the decay of Mo-99. Currently, Iran's demand for Mo-99 is 120 Ci per week. More than 90% of the Mo-99 in the world is produced via U-235 fission. The supply chain of this radioisotope includes the Uranium target supplier, the nuclear reactor, the Mo-99 processing facility, and the Mo-99/Tc-99m generator manufacturer. Investigation of the domestic existing facilities of Iran shows that its production is feasible inside the country. The present study focuses on the Mo-99 production chain in Iran and presents the appropriate radiochemical method. Uranium targets in the miniplate form with irradiation capability in TRR were accepted as feed for processing unit facilities. According to the special limitations of Iran, the Modified AMOR process, which is a combination of AMOR and ROMOL processes, is identified as the appropriate method for the available U3O8-Al/Al targets. The researches and the experimental activities are proposed based on this method.

Poly (methyl methacrylate) (PMMA) is an inexpensive polymer widely used in different applications such as the fabrication of optical tools, sensors, and microfluidic medical devices. In the present study, the effect of emitted radiations from a Cobalt-60 gamma source with emission doses between 10-30 kGy on the optical properties of this polymer is investigated. The effect of gamma radiation on optical transmission and absorption, bandgap energy, Urbach energy, dispersive energies, and refractive index of this polymer is investigated, and the obtained results are presented. The results indicate that the absorption coefficient, the refractive index, and the optical conductivity of the PMMA polymer increase within this range of gamma radiation doses. The wavelength-dependent magnitudes of these quantities are measured and represented as graphs. Within this irradiation dose range, the bandgap energy of the polymer gradually decreases, which is in agreement with the optical conductivity increase of the samples. The results indicate the reduction of the bandgap energy of polymer from 4.461 eV to 3.482 eV by 30 kGy gamma irradiation dose. Increment of the refractive index and the absorption coefficient and the enhancement of the optical conductivity with the represented data in this work can be used to fabricate new tools with improved capabilities.

In the present work, using different volume percentages and different sizes of TiO2 (Titania) and Al2O3 (Alumina) nanoparticles, the important and basic parameters of VVER-1000 reactor including dynamic parameters of reactor (such as temperature reactivity coefficients) that play an important role in reactor dynamic analysis and core safety requirements are calculated. For this purpose, at the first the equivalent cell of fuel rod and the surrounding coolant nanofluid in the hexagonal fuel cell of the VVER-1000 reactor is determined. After that, by using the ANSYS FLUENT simulator software, thermo hydraulic calculations are performed in different concentrations and sizes of nanoparticles to study their effect on the parameters of the heat transfer coefficient, fuel, and coolant temperature. Then, using WIMS and CITATION neutron computing codes, the reactor core is simulated and the effect of coolant nanofluid and fuel temperature changes on the effective multiplication factor is calculated and analyzed. The fuel and coolant temperature reactivity coefficients are determined. These coefficients are calculated by varying the concentration and size of nanoparticles in the coolant.