Mohamed S. El_Tokhy

Development of coincidence summing and resolution enhancement algorithms for digital gamma ray spectroscopy

This paper discusses the correction of some of the main problems of digital gamma ray spectroscopy. These problems are the coincidence summing and energy resolution. The coincidence summing effects are evaluated using analytical techniques. Correction is made at different energies for both 137Cs and 60Co radioisotopes. A simple relation is derived between the coincidence summing correction factor and the energies under the conditions of the system configuration. This relation is deduced using the least square approximation method. Consequently, correction can be done at different energies of radiation sources under the constraints of the measured conditions. Furthermore, the coincidence summing algorithm is validated through comparison with published experimental results in the literature and good agreement is found. Coincidence summing correction factors are used to correct the values of the Full Energy Peak (FEP) efficiencies. Correction factors were calculated for predominant gamma emissions significantly affected by coincidence summing effects for both 137Cs and 60Co point sources. Also, a correction algorithm for the resolution–degradation in scintillation (NaI (TI)) gamma ray detectors using derivative methodology is presented. The derivative methodology is implemented by weighted sum of the original signal, the negative of its second derivative and the positive of its fourth derivative. We noticed that using both derivatives in combination improves the energy resolution, which is enhanced by 24.03%. From the obtained results, the FEP efficiency was enhanced by 1.58% due to coincidence summing correction. Consequently, accurate determination for the source activity can be achieved.

Block diagram modeling of quantum dot infrared photodetectors

The main objective of this paper is to evaluate the performance of quantum dot infrared photodetectors (QDIPs). The tools that we are used are the VisSim environment, along with the block diagram programming procedures. The benefits of using this modeling language are the simplicity of carrying out the performances measurement through computer simulation instead of setting up a practical procedure which becomes expensive, as well as the difficulty of its management. The roles that the parameters of fabrication can play in the characteristics of QDIPs are discussed through developed models implemented by VisSim environment. VisSim can be a powerful supplement to model the Poisson equation. MAPLE software is used to devise this model. The theoretical result confirms that implicit solution of QDIPs governed by dynamic equations provides exact handling of the device performance. As an example, dark current, photocurrent, and detectivity are investigated. In order to confirm our models and their validity on the practical applications, we make a comparison between the results obtained by MAPLE, VisSim, and that experimentally published, and full agreement is observed. The implemented models can help designers and scientists optimize their devices to meet their requirements.

Model Development of Quantum Dot Devices for γ Radiation Detection Using Block Diagram Programming

The main objective of this paper is to develop a model of quantum dot (QD) devices for incident γ radiation detection. A novel methodology is introduced to characterize the effect of γ radiation on QD detectors. In this methodology, we used VisSim environment along with the block diagram programming procedures. The benefit of using this modeling language is the simplicity of carrying out the performance’s measurement through computer simulation instead of setting up a practical procedure, which is expensive as well as difficult in management. The roles that the parameters of fabrication can play in the characteristics of QDs devices are discussed through developed models implemented by VisSim environment. The rate equations of the QD devices under γ radiation are studied. The effect of incident γ radiation on the optical gain, power, and output photon densities is investigated. The implemented models can help designers and scientists to optimize their devices to meet their requirements.