mojtaba mokari

X-ray detectors, which generally enjoy very good detection efficiency and spatial resolution, have many applications including in radiography and basic research. Many of the existing radiographic methods are extremely inefficient and time-consuming, making them improper for real-time applications. A solution to avoid such a problem has been to develop structured scintillation films such as CsI, which have high density and fast response, and at the same time, have the possibility of being grown as compact micrometer structures – suggesting a way to attain better image qualities. Employing the Geant4 Monte Carlo toolkit, we have used a simple geometry to serve as a radiography system, which includes a polymer layer as a camera, a structured layer of micro-columnar scintillators as x-ray converters, and an aluminum layer as a light reflector. Hence, for pencil-beam x-rays we investigated the dependence of blurring on the production depth of the resulting optical photons.

In recent years, the use of machine learning methods in various fields of agriculture is increasing, and these methods provide us with very good information for predicting and checking different levels of performance in plants. In the current research, according to the results of the preliminary experiment carried out previously with specific levels of salinity stress and fertilization (salinity stress levels of zero, 75 and 150 mM sodium chloride and fertilization levels of zero and 3 grams per liter of silica) which were previously carried out and using the nonlinear regression model (NLR) and Python programming language, the morphological and physiological traits of the fenugreek medicinal plant at the newly defined levels of salinity stress and silica fertilization (salinity of up to 300 mM level and silica fertilization in two levels of 1 and 2 grams per liter) were predicted without conducting practical tests and based on the levels of salinity and initial fertilization. The non-linear regression model is a widely used algorithm in data analysis where the relationship between variables is non-linear and can create meaningful relationships between variables using non-linear functions. The results showed that the positive effect of silica on the amount of chlorophyll fluorescence (Fv/Fm) can be seen from zero to 180 mM salinity level and the amount of greenness index (SPAD) from zero to 100 mM salinity level. It seems that according to the results of the present research, it is possible to use machine learning to investigate and analyze the morphological and physiological characteristics of the fenugreek medicinal plant at other defined levels of salinity stress and other defined silica fertilization with no need conduct a practical experiment.

Carbon ions’ dose distribution, in comparison with lighter hadrons, has certain therapeutic advantages due to their relatively higher biological effectiveness in tumors. Simulating the physical and chemical interactions of carbon ions in a sphere of liquid water of cellular scales, we derived the mean number of deposited energies per unit dose per a DNA segment of 216 bp as a function of deposited energy. As such, the frequency of complex damage was obtained from the point of view of a multiplicity of damage points on the DNA strands. Furthermore, the damage yields for different types of single- and double-strand breaks were obtained and, specifically, the mean number of simple single- and double-strand breaks per DNA segment were calculated as a function of deposited energy

Due to physical and chemical interactions with the cell DNA, ionizing radiations induce early and late damage to the genetic material. This type of damage, which is mainly caused by single-stranded and double-stranded breaks in DNA, and if not repaired by the cell, can lead to genetic mutations or cell death. In this research, the DNA damage of living cells, induced by protons and carbon ions, which are of great importance in radiation therapy studies, has been investigated with the MCDS code. In order to check the accuracy of the MCDS code results in this research, the probability of each type of damage and the yields have been calculated and compared with the results of previous works with Geant4-DNA. The results of this research, especially double-strand breaks, are very close to the results calculated with the Geant4-DNA code. There are also differences in the results due to the difference in the cross-sections of the two codes, especially in ionization and excitation interactions, as well as the reaction rates of chemical radicals. The results of this research regarding the efficiency of double-strand breaks can be very useful in the planning of treatment with protons and carbon ions.

Microdosimetry is an approach that can be very effective in improving the quality of radiation therapy. Based on the possible concept of deposited energy in microbiological tissues and environments, this knowledge can help to calculate and examine the quantities related to the effect of radiation. In this research, using the Geant4-DNA code in conjunction with experimental cross-sections and the µ-randomness method, the microdosimetry quantities known as the frequency-mean lineal energy and frequency-mean specific energy were calculated for low-energy electrons. The calculations concerned cylinders that are comparable in size with living organisms such as DNA, nucleosome, and chromatin fiber, distributed randomly in a sphere of water with a diameter of about the average size of the nucleus of human cells. The results were compared with the ones obtained based on the default cross-sections of Geant4-DNA. We found that the average values of (frequency-mean) lineal and specific energy calculated with experimental cross-sections were larger than those calculated with default cross sections. The maximum difference of these quantities was observed, in the so-called small and medium cylinders, at 0.1 keV and, in the large cylinder, at 0.3 keV. Also, for a volume comparable in size to DNA, a good correspondence between the results of frequency-mean lineal energy with experimental cross-sections and the electron DNA-damage in the cell was observed.

In this work, the platinum and gold nanoparticles colloids are fabricated by 18 ns pulsed laser ablation of pure platinum and gold plates in the distilled water. The formation of the nanoparticles has been evidenced by taking the UV-Vis absorption spectrum and observing the surface plasmon absorption band of gold and platinum nanoparticles as well as by transmission electron microscopy.The nonlinear optical properties of the platinum and gold nanoparticles in distilled water are measured by the closed- aperture Z-scan technique under exposure to a low- power continuous-wave laser at a wavelength of 532 nm. The observed asymmetric nature of the Z-scan measurements along with the fact that the laser light is CW suggests that the origin of the nonlinear refractive index is thermo-optic. The optical limiting performance of the platinum and gold nanoparticles are characterized by exposure to CW laser operating at a wavelength of 532 nm. The results show that nonlinear self-defocusing effect increases the performance of the optical limiting. The engineering of the experimental geometry can accomplish the tunability of the limiting threshold of optical limiters.

By defining random quantities related to microscopic structures, microdosimetry can provide accurate information about the effects of radiation. Using the µ-randomness method and the Geant4-DNA code, in a sphere of water for low energy electrons in the energy range of 0.1 to 4.5 keV, the microdosimetric values of the frequency-mean lineal energy, dose-mean lineal energy, frequency-mean specific energy, and dose-mean specific energy were calculated. In this study, target volumes including cylinders with dimensions (height × diameter) of 23 × 23 equivalent to DNA volume, 50 × 100 equivalent to nucleosome volume, and 300 × 300 angstroms equivalent to the volume of chromatin fiber were selected. Examining the frequency-mean lineal energy and dose-mean lineal energy, it was observed that the trend of changes in the energy of the primary electrons is similar to the trend of changes in the damage of the same electrons in the DNA. The research results are also compared with the existing results of the simulation with the PITS and KURBUC codes. Differences in the results of this study were observed with the results of PITS and KURBUC codes, which is due to differences in the cross-sections of the electron used in the codes under study. In the Geant4-DNA code, for example, for low-energy electrons, the ionization and excitation cross-sections are smaller than those obtained by other codes.

The ionizing radiations, through physical and chemical processes, lead to simple and complex single- and double- strand breaks, as well as base lesions to the DNA. In this study, taking into account all the physical and chemical processes involved in the interaction of ionizing radiation with matter, the initial damage induced to DNA was evaluated for 5.7 MeV alpha-rays from Radon 223 isotope. The probability of damage types was calculated in terms of the energy deposition and the probability of direct and indirect damage was investigated as a function of the number of breaks. The results show that, for low deposited energies, the probability of single-strand breaks is more than double-strand breaks. As the amount of the deposited energy increases, this pattern is reversed and the probability of various types of double-strand breaks dominates. The yield of double-strand breaks in the DNA segments, as a main target in radiotherapy, was calculated by the method of energy deposition in DNA samples and compared with previous works. Our results are in good agreement with experimental results.