Sharif Digital Repository

The present M.Sc. thesis consists of two sections including the static calculation and neutron noise calculation in rectangular and hexagonal geometries. The multi-group, two dimensional neutron diffusion equations and corresponding adjoint equations are solved in the static calculation. The spatial discretization of equations is based on Average Current Nodal Expansion Method (ACNEM). Size of nodes is the same size of the fuel assemblies in modeling both of rectangular and hexagonal geometries. The results are benchmarked against the valid results for BIBLIS-2D and IAEA-2D benchmark problems. In the second section, neutron noise calculations are performed for two types of noise sources,... 

Magnetic resonance imaging (MRI) is a highly efficient method that can provide acceptable contrast between soft tissues. But the big disadvantage of this method is that its acquisition is slow. To find the reason of being time-consuming should the procedure be surveyed. In the magnetic resonance imaging, location information obtained using phase and frequency encoding gradients. So the output is matrix of image data in the frequency domain, which is called k space. For the formation of the k space phase, need to apply gradients several times and this is the main reason of dullness of the system. Therefore, in this project using software methods try to reduce the scan time as possible. Among... 

The present ph.D. thesis consists of three sections including the static calculation, neutron noise calculation and neutron noise source unfolding in VVER-1000 reactor core. The multi-group, two dimensional neutron diffusion equations and corresponding adjoint equations are solved in the static calculation. The spatial discretization of equations is based on Galerkin Finite Element Method (GFEM) using unstructured triangle elements generated by Gambit software. The static calculation is performed for both linear and quadratic approximations of shape function; baesd on which results are compared. Using power iteration method for the static calculation, the neutron and adjoint fluxes with the... 

High purity Germanium (HPGe) detector is a sub branch of semiconductor detectors which has very good resolution, very little dead time, able tobuild in large dimensions and suitable for any condition that it is using in vast fields from space investigation to radiation therapy. this detector is usually used to detecting gamma radiations furthermore the best resolution can be attained with decreasing leakage current. for analyzing about operation of the HPGe detector, it needs to initiate a model of this detector. in this studing has been used modelGEM-15190,POP-TOP which is built by ortec company. for initiating, it was used liquid nitrogen and accessory equipments like high voltage supply,... 

The analysis of gamma-ray spectra of low resolution detectors is difficult and sometimes impossible, as a result of photo peak’s overlapping. The usual methods of radiation spectra analysis based on fitting of peaks to mathematical curves or detecting of peaks with numerical calculation, are valid for high resolution detectors. However these methods are less successful for lower resolution detectors such as the common scintillators. The wide peaks in the spectrum maybe overlap and make it difficult to analysis. To solve this problem, we test here a method, based on the use of the artificial neural network. At first spectra of elements are converted to the patterns which are suitable for the... 

Radiation detection techniques have important applications including prompt gamma neutron activation analysis (PGNAA), radiotherapy dose measurement, medical imaging and homeland security. Pulse height distribution is also a useful parameter in Radionuclide identification. Gamma ray spectroscopy analysis is a common technique in measuring of radiation field to identify the radioactive source.
Probabilistic methods are commonly used for numerical simulation of Pulse height distribution. In Monte Carlo methods, each history is individually tracked and details of interactions are available. Using the Monte Carlo methods for calculation of pulse height distribution leads to more real... 

Microrobots design and manufacturing has been one of interesting fields in robotics in recent decades. They have been designed in various types so far. In this paper a two-leg microrobot is simulated and controlled by using LuGre friction model.
The proposed microrobot is driven by a piezoelectric actuator mounted between centers of two legs. The piezoelectric is actuated by a frequency near the natural frequency of the robot. The nonlinear dynamical equations of the system are obtained considering LuGre friction model. To control the system, the equations of motion are linearized using feedback linearization method. Then a stabilizing control law is designed and the robot model is... 

Neutron fluctuations in both low and high power reactors provide important information about the system. The origins of these fluctuations are different in both regimes. In low power the branching process is the reason of these fluctuations. But the random nature of technological processes such as boiling in the reactors cooling and mechanical structure vibrating such as control rod and fuel rod created the neutron noise. Mathematical descriptions and applications of neutron noise for each mode are different. In common mode, fluctuations in the neutron detection system, determine some parameters and determin the start abnormality in system. In this study the spatial dependence of the cross... 

Localization of a neutron point source using a designed computer program namely “MCMC-MATURE” is performed. The computer program analyses several detector responses in some certain media by Markov Chain Monte Carlo (MCMC) method and a new iteration algorithm. Identification of the possible regions of source position would be found by analyzing the initial fluxes generated by mesh tally of MCNPX computer code. The designed computer program is capable to generate the flux between detectors. “Regular-Sequential”, “Irregular-Sequential” and “Non-Sequential” are three methods used for sampling the generated random number in two dimensions. Each sample multiplied by a sampling function and lead to... 

In this project, the final goal is to create a team consisting of a UGV and a quadrotor capable of relative tracking and coordinated landing, with focus on quadrotor control. What we mean by cooperative control in this project is control of quadrotor for the purpose of cooperation with a UGV; This should not be mistaken with another sense of cooperative control in which the control algorithms are developed for both of the robots or are based on the interactive dynamics of the robots.In order to accomplish this goal, an experimental testbed consisting of a quadrotor and a UGV capable of communication and data exchange was developed as a first step. The quadrotor was constructed using... 

Precise knowledge of the laws which govern a system is of interest for two reasons. First, it paves the way to understand the subtle behaviors of the system, which are not understandable from simpler models of the system. Second, it helps in the design of experimental requirements needed to observe these behaviors. The behavior of neutrons in a system, which could be a reactor or a detector, is stochastic from two perspectives. First of all, since the place of the atoms of a medium are randomly sited, at least from a neutrons point of view, the collision sites are random places, which contributes to the stochasticity of the transport phenomena. This type of randomness is somewhat similar to... 

In operating nuclear reactor core, fluctuations (deviations from normal operating conditions) are usually produced and propagated. These fluctuations can be due to control rod vibrations, inlet coolant temperature fluctuations, inlet coolant velocity fluctuations and so on. The induced neutron noise can be detected by in-core neutron detectors. Noise source identifications (such as the type, location and propagating velocity) as well as the calculation of the dynamical parameters (such as moderator temperature coefficient in PWRs and Decay Ratio in BWRs) are of the main applications of the neutron noise analysis in power reactors.
Investigating the propagation noise in PWRs (specifically... 

The emergence of complex equations in engineering sciences leads to development of numerical methods for solving these equations. Obviously, each of the proposed Algorithms and various methods in this field were evaluated according to the limitations of time, software and hardware and based on these limitations the advantages and disadvantages of these methods were determined. Direct Discrete method is one of the modern methods used in solving the conservation equations. In this method, in addition to the advantages of numerical methods, equations will be produced in discrete space to avoid involving with differential equations. This method was first studied in the field equations. The...