Sharif Digital Repository

This paper presents a bit-flip tolerance in SRAM-based FPGAs which suffers from high energy particles, alpha and neutrons in the atmosphere. For each of protections, the applicability, efficiency and implementation issues are discussed. Moreover, the area, the power and the protection capability of the methods are mentioned and compared with previous work Based on the results of experiments and their analysis, one method is selected as best one. The selected method is much better than previous work e.g., duplication with comparison, triple modular redundancy which impose two and three area and power overheads, respectively. © 2007 IEEE  

The objective of this paper is to introduce a new direct method for neutronic calculations. This method, called Direct Discrete Method (DDM), is simpler than the Neutron Transport Equation and more compatible with the physical meanings of the problem. The method, based on the physics of the problem, initially-runs through meshing of the desired geometry. Next, the balance equation for each mesh interval is written. Considering the connection between the mesh intervals, the final discrete equation series are directly obtained without the need to first pass through the set-up of the neutron transport differential equation. In this paper, a single and multigroup neutron transport discrete... 

In this paper, we describe an innovative method to model and solve spatio-temporal behavior of nuclear reactor cores via three-dimensional multilayer cellular neural networks. This method uses electrical elements and the existing duality between neutronic and thermal-hydraulic parameters of nuclear reactors. The relevant electrical circuit can be simulated by existing professional electrical circuit software. This research goes beyond our previous efforts to use a neural computing approach in the nuclear field. Modeling and solving simple nuclear reactor kinetic equations is now expanded to a complete dynamic calculation, integrating the core thermal-hydraulic models and the relevant... 

In an attempt to explore the significance of transport theory in neutron noise, localization of a noise source by Green's function based on transport theory is investigated. There are considerable differences between Green's functions based on diffusion and transport, such as small dimensions, near edges, high heterogeneity medium and high-frequency source of perturbation. These differences are expected to significantly impact unfolding, reconstruction, and identification of the neutron noise source. Improvement in noise source unfolding methods is essential in terms of safety aspects and reactor performance enhancement. Since gaining the ability to monitor nuclear reactor based on noise... 

The purpose of the present study is to develop the neutron diffusion solver and neutron noise simulator based on the Boundary Element Method (BEM). The 2-D, 2-G neutron/adjoint diffusion equation and corresponding neutron/adjoint noise equation were solved using the mentioned method. The developed neutron static and noise simulator based on the finite element method gives accurate results when the more number of the elements is used. The motivation of the present research is to use the boundary element method to reduce the computational cost. The boundary element method attempts to use the given boundary conditions to fit boundary values into the integral equation, rather than values... 

In this study, the SD-HACNEM (Sharif Dynamic - High order Average Current Nodal Expansion Method) neutron noise simulator in two energy groups using a second-order flux expansion method for two-dimensional rectangular X Y-geometry has been developed. In the first step, the calculations were performed for the steady state and results of ACNEM (Average Current Nodal Expansion Method) and HACNEM (High order Average Current Nodal Expansion Method) were examined and compared. To solve the problem, the power iteration algorithm has been used to calculate the distribution of neutron flux and neutron multiplication factor by considering the coarse-mesh (each fuel assembly one node). To validate the... 

Proton therapy (PT) is an emerging external beam radiation therapy characterized by superior dose distribution compared to conventional modalities. In the present study, an optimal GATE model was developed and then validated for a double scattering proton nozzle based on the previously constructed model. To this aim, a double scattering treatment nozzle was modeled in the GATE platform. To accelerate the GATE simulations, a virtual range modulation wheel (vRMW) and a variance reduction technique (VRT) were implemented. Proton beam flatness, symmetry, and delivery efficiency, secondary neutron dose, and dosimetric performance were characterized through a set of GATE simulations. The findings... 

The safety and optimal performance of nuclear reactors require online monitoring in the core. The present paper describes a method that avoids the solution of the time-dependent neutron diffusion equation, and it uses online readings of the fixed in-core neutron detectors to reconstruct the three-dimensional (3D) neutron flux distribution. The essential idea of the nodal synthesis method is the separation of time and space-dependence of the neutron flux distribution. The time-dependent section of the flux distribution is determined by in-core neutron detector readings, and the space-dependent section is obtained from pre-computed harmonics of the neutron diffusion equation. In online... 

Applying the available neutron flux for medical and industrial purposes is the most important application of research reactors. The neutron radiography system is used for non-destructive testing (NDT) of materials so that it is one of the main applications of nuclear research reactors. One of these research reactors is the 5 MW pool-type light water research reactor of Tehran (TRR). This work aims to investigate on materials and location of the beam tube (BT) of the TRR radiography system to improve the index parameters of BT. Our results showed that a through-type BT with 20 cm thick carbon neutron filter, 1.2 cm and 9.4 cm of the diameter of inlet (D1) and output (D2) BT, respectively... 

Using tight binding band picture for 2D graphite, and the Hubbard interaction, recently we obtained a gapless, neutral spin-1 collective mode branch in graphite [Phys. Rev. Lett. 89, 016402], In this paper we present a detailed RPA analysis of the Neutron Scattering cross section for this collective mode. Near K-point and very close to Γ-point, the intensity of neutron scattering peaks vanishes as q3. This is shown using a simple Dirac cone model for the graphite band structure, which captures the small-q behavior of the system. As we move away from the Γ- and Κ-points in the Brillouin zone of the collective mode momenta, we can identify our collective mode quanta with spin triplet excitons... 

The bond valence sum method has been developed to high pressures considering B0(p) for calculating the valences of atoms. This approach has the advantages of finding a universal B0(P) for all the atoms -at least in YBCO, ability to evaluate the valency of each atom, and charge neutrality requirement of the unit cell. As a result, a new structural refinement has led to a more exact structural detail. The position of apical oxygen is found to be specially crucial for hole distribution between the superconducting CuO2 planes and Cu-O charge reservoir chains. Under pressure, the hole concentration in CuO2 planes increases, but in the Cu-O chains decreases, consistent with the pressure induced... 

The normal state resistivity of single phase polycrystalline Gd(Ba 2-xPrx)Cu3O7+δ samples with 0.0 ≤ x ≤ 0.50 have been investigated. The two-dimensional variable range hopping is dominant in the normal state resistivity of the samples. The conduction shows that Pr-doping strongly localizes the carriers in normal state, and finally causes the suppression of superconductivity. Based on the resistivity measurements, the effect of Pr substitution in 123 structure of HTSC at Gd or Ba site is to increase the pseudogap temperature Ts, although, Pr at Ba site has a stronger effect on the suppression of T s and superconductivity. Pr-doping not only reduces the carrier density and induces pseudogap,... 

The objective of this paper is to introduce a new numerical method for neutronic calculation in a reactor core. This method can produce the final finite form of the neutron diffusion equation by classifying the neutronic variables and using two kinds of cell complexes without starting from the conventional differential form of the neutron diffusion equation. The method with linear interpolation produces the same convergence as the linear continuous finite element method. The quadratic interpolation is proven; the convergence order depends on the shape of the dual cell. The maximum convergence order is achieved by choosing the dual cell based on two Gauss' points. The accuracy of the method... 

Thermal neutron analysis (TNA) technology has been used for the non-destructive detection of explosives. The system uses a relatively weak 252Cf neutron source (1.03.107 n/s) and two 3″3×″ NaI(Tl) detectors. The presence of explosives is confirmed via detection of the 10.83 MeV prompt gamma-ray associated with nitrogen decay. The MCNP4A code was used to simulate the neutron and gamma transport through the system. The thermal neutron flux in the activation position was measured using gold and indium foils. The measured thermal neutron flux was lower, by not more than 9.5%, than that of simulation. In this report the results of the preliminary tests on the system are described  

Knowledge of the complete multiaxial residual stress distribution in engineering components is essential for assessing their integrity. Often, however, only limited measurements are made. Here, an analysis is presented for determining the multiaxial distribution from a limited set of measurements. These measurements are used with an assumed plastic strain distribution. Residual stress measurements were made on hot forged and shot blasted steel bars using X-ray and neutron diffraction techniques. The residual stresses were measured on the surface and at selected interior points of the specimens. The predicted multiaxial distributions were compared with experimental measurements obtained using... 

In this study, new method for NAA purposes at 30 kW Isfahan MNSR is suggested. An algorithm based on ANN is proposed to quantitatively predict the unknown elements with no need standard sample. A three-layer feed-forward ANN with back-propagation algorithm has been used to determine concentration of selenium and fluorine in Multiple Sclerosis patients and healthy people blood samples. Predicted concentration of elements show good agreement between new method and experiment results. The correlation coefficient between the experimentally determined and predicted values are 0.99104 and 0.99364, respectively. This method is a rapid and precise approach for elemental analysis. © 2022, Akadémiai... 

In this study, the Geant4 toolkit is utilized to present a new approach for simulation of the D-T interaction. The neutron production cross-section and the energy/angle distribution of neutrons produced as the D-T data libraries are incorporated in the Geant4, and their performance is evaluated. The spectra shape of the produced neutrons of the D-T interaction simulated by the Geant4 show good agreement compared to the results of the comparative codes (i.e. MCUNED, ENEA-JSI, and DDT). However, some differences are observed, especially, in angular range of 90-95 degrees. The reason for these differences as well as the results of the proposed approach in comparison with the results of the... 

In this study, in order to maximize the reaction rate of neutron activation (NA), an approach using combination of the MCNP code, the feed-forward neural network with the Bayesian regularization (FFNN-BR) learning algorithm, and the genetic algorithm (GA) is proposed. The MCNP code calculates the reaction rates based on the different moderator dimensions/ target positions. The calculated reaction rates with appropriate features (i.e. RT, R2S, and Z2S) are applied for training of the FFNN-BR. The trained neural network is utilized for estimating the reaction rates of the generated individuals by the GA. The results show that the trained neural network estimates the reaction rates with... 

The alkaline treatment condition plays a crucial role in governing the ultimate properties of flax fibers. In this study, flax fibers were modified with mild alkalization and severe mercerization conditions to give fundamental insight into how the molecular-scale changes in cell wall fine structure and cellulose supramolecular structure can affect the macroscopic properties of fibers. SEM, FTIR, XRD, TGA, and DSC techniques were employed to characterize the variations in morphology, composition, crystalline structure, and thermal properties of fibers. Also, tensile tests evaluated their reinforcing performance in polypropylene-based composites. The results indicated that alkalization in 5%...