Majid Khorsandi

Monitoring the level of radioactive contamination and the type of radiation in the environment is very important for the protection of facilities, employees, and people. Phoswich detector is one of the useful tools to identify different radiations and separate them from each other using different scintillating crystals. However, their design can be very diverse based on the type of particles analyzed and various parameters of scintillating crystals and needs optimization to have maximum efficiency. This work aims to optimize the scintillating crystal layers for the design of the three-layer alpha-beta-gamma phoswich detector based on Monte Carlo radiation transport calculations. The selection of the appropriate model for the type and thickness of each layer is based on the optimization of parameters such as energy accumulation, produced scintillation optical photons, attenuation of optical photons, and scintillation decay time …

Combination of two or three dissimilar scintillator materials as a radiation detector has found major role in environmental radiation monitoring. In this paper, a three-layer Phoswich detector including BC-400, YAG, and CsI was designed to efficiently discriminate gamma-ray in the beta events up to 3.2 MeV using a simple rise-time discrimination method. MCNPX Monte Carlo code was used to obtain interaction probability of beta and gamma-rays as well as optimum thicknesses of the layers in the designing process. The optical transport of the system was simulated by GEANT4. In this regard, the pulses from simultaneous beta-gamma emitter sources were detected and discriminated based on pulse's rise-time so that the minimum number of gamma-ray contaminating events was observed in the beta spectrum. The results showed that using the proposed configuration and the method, output pulses with a rise-time …

The performance characteristics of InGaN Double-Quantum-Well (DQW) Laser Diodes (LDs) with different barrier structures were studied numerically by Integrated System Engineering Technical Computer-Aided Design (ISE TCAD) software. Three different kinds of structures of barriers including quaternary AlInGaN and AlInGaN/AlGaN superlattice barriers were used and compared with conventional GaN in InGaN-based laser diodes. Replacing the traditional GaN barriers with quaternary AlInGaN increased holes and electrons flowing in the active region and thus, the radiative recombination enhanced the output power. However, it did not reduce the threshold current due to hole and electron overflowing. To investigate the ways of greatly reducing the threshold current, the structure consisting of AlInGaN/AlGaN superlattice barriers was proposed. The simulation showed that electrical and optical characteristics such as output power, Differential Quantum Efficiency (DQE), and slop efficiency were significantly enhanced for LDs containing superlattice barriers compared to the basic structure. This is while the threshold current was considerably reduced. The enhancement was mainly attributed to the improvement of hole injection and also the blocking hole and electron overflowing caused by the reduction of polarization charges at the interface between the barriers, the well, and the Electron Blocking Layer (EBL).

Charged coupled device (CCD) is an imaging sensor that can be used as a digital radiation position-sensitive detector in space applications, industrial and medical imaging, etc. Commonly, the CCDs used for X-ray imaging are expensive and needed more complicated control, electronic boards. In this work, a simple and low-cost commercial CCD model (TCD1304AP) has been used to implement X-ray imaging. Moreover, a CsI(Tl) scintillation crystal with different thicknesses of 2 and 5 mm has been utilized as an X-ray to light photon converter. The driving and data acquisition boards have been designed in straightforward implementation, which can be easily performed. Also, the appropriate integration times have been set to 10 ms and 420 ms for use in cases with and without scintillation crystals respectively. The results show that this sensor has an admissible response to X-ray imaging. There is about a below 8 …

Quadrupole mass filter device is a key component in mass spectrometers which analysis ion particles based on their mass to charge ratio; this mean by applying a specific potential on the instrument, crossing most of ions diverge and lost and just some are survived through crossing mass filter. Using multi-physics simulation, one may obtain deep knowledge on performance of the filter and investigate the effect of different variable parameters on operation of the instrument. In this paper by implementing COMSOL multi-physics software the impact of operating line slope stability, ion beam position displacement, and oscillation of potential field on ions filtering is investigated.

Volume fraction and regime identification are considered as two main goals in the multiphase flow measurement. By developing the applications of artificial neural networks (ANN), new approaches have been introduced in the multiphase measurements. In the present work, prediction of gas volume fraction and identification of five different flow regimes including Bubble, Dispersed, Pluged, Annular, and Slug regimes were carried out using the simplest form of a radiation measurement system and proposing a simple structure of ANN including two independent MLP networks which are working in parallel. All data used for training and testing the networks were recorded using a simple radiation-based setup involving a137Cs gamma-ray source and one NaI(Tl) detector in the experimental setup with real dynamic conditions of fluids in a test loop. Extracted features from the recorded spectrum by the detector include …

Gas-liquid two-phase flow is probably the most important form of multiphase flows and is found widely in the oil industry. The accurate prediction of the air and water flow-rates are important in two-phase flow. Nowadays, multiphase flow-rates measurement by gamma-ray attenuation technique is known as one of the most common precise methods. In this work, the air and water flow-rates independent of flow regime changes were accurately predicted within a two-phase flow loop in the laboratory. For this purpose, a combination of single beam gamma-ray, single detector and artificial neural network (ANN) were used in order to predict the flow-rates in the bubble, plug, slug, annular and dispersed regimes of gas-liquid two-phase flows. Two different types of neural networks (GMDH) were developed. The networks were developed based on four features extracted from recorded pulse height distribution in a dynamic …

In this work, the air and water flow-rates were accurately predicted within a two-phase flow loop using features extracted from a simple detector spectrum, independently of the changes in the flow regime. In this regard, a new method based on a single beam-single detector using single-energy of gamma-rays was proposed. The gamma-ray attenuation setup combined with Artificial Neural Network (ANN) was used to predict the flow-rates in various regime of gas–liquid two-phase flows such as bubble, plug, slug, annular and dispersed regimes. Moreover, the ANN was developed based on four features extracted from the recorded pulse height spectrum in the dynamic condition of the fluids. The results showed that the air and water flow-rates can be measured with an average of Mean Relative Error (MRE) less than 4.5%. Overall results revealed that using the proposed method, prediction of the flow-rates can be …