New Research in Physics

Abstract Multipacting which occurs due to high amplification in secondary electrons, is a typical phenomenon in the radiofrequency structures. The Coulomb force between the secondary electrons induces space charge and consequently saturates the multipacting phenomenon. A realistic study of this phenomenon requires considering the effect of space charge. Simulation of the space charge effect by CST PIC STUDIO software is not simply possible and pose some challenges for users. In this paper, it is described how to consider space charge in a single-side multipacting simulation for a simple model. The effect of space charge on the simulation results has been investigated and the threshold of the the radio frequency field amplitude for multipacting occurrence has been obtained.

Abstract Optical pumping is a process used in physics and quantum mechanics to manipulate the energy levels of atoms or ions using light. It involves the absorption and emission of photons by atoms, which can change their electronic configurations and energy states. In this paper, optical pumping with Liouville equation approach is used to investigate optical pumping in alkali atoms. For this purpose, circularly polarized light is applied to the atomic system, which causes a transition between atomic sublevels and changes the population of sublevels. Also effect of relaxation and repopulation are considered in the evolution of the population sublevels. Here, we use optical pumping with Liouville equation approach for investigation of population evolution in Cesium atom.

Abstract In this article, the boundary layer of an active collisional thermal plasma in contact with a metallic plane wall in the steady state has been studied using the plasma fluid equations. The spatial variations of plasma functions including the electric potential, ion kinetic energy and the I − V characteristic curve have been investigated from the plasma-presheath edge to the floating point and the effects of the plasma parameters including, ion temperature, ion-neutral elastic collision and ionization rate on the plasma functions are investigated. In the full solution approach of the plasma boundary layer, the fluidal equations experience a singularity when the ion velocity grows up from zero at the plasma-presheath edge and reaches to the ion thermal velocity . Totally removing the singularity creates a well-defined eigenvalue problem with a smooth solution to the model equations. By using the smooth solution, dependency of the plasma functions to the plasma parameters including, the ion temperature, the ionization rate and the elastic collision frequency have been examined.

Abstract "Algebraic cluster model" (ACM) is used to describe the relative motion of the cluster by considering vibrational and rotational degrees of freedom.In this research, using the two-body ACM Hamiltonian, the quantum phase transition in the transition region U(3)↔O(4) for odd nuclear structures such as: ⁸Be،⁹B، ⁹Be, and ¹⁰B has been investigated. The energy surfaces, the expectation value of the boson number operator as a function of the control parameters of the calculated Hamiltonian, and also the effect of pairing the odd nucleon with the even-even boson nucleus at the critical point are discussed. Experimental data confirm the numerical results.

Abstract We investigate the stellar mass-size relation of galaxies and their specific star formation rate (sSFR) in both high-density and low-density environments. The study is based on data obtained from the Millennium simulation in z=0. According to our research, the size of massive elliptical and spiral galaxies is unaffected by their environment. These studies show that low-mass spiral galaxies are larger in voids than in dense environments. Also, among the elliptical galaxies, we observed a group of low-mass galaxies that were more compact despite the same mass. Due to the effects of ram pressure stripping and gravitational interaction, massive spiral galaxies tend to have lower star formation rates. The size of low-mass spiral galaxies is affected by dense environments, resulting in larger sizes in voids. Our analysis indicates that the abundance of cold gas has a greater impact on star formation rate than the halo mass of galaxies in all environments.

Abstract In this article, The silicon-based PIN-type photodiode were designed and fabricated for alpha radiation detection. The energy resolution is one of the most important parameters in this type of detectors; the increase in energy resolution depends on the reduction of the fabricated photodiode dark leakage current. So one of the most important goals in this research is Design and Fabrication of photodiode with low leakage current and high energy resolution. The C-V and I-V electrical tests and the 241Am alpha spectrum measurement are carried out after the completion of the manufacturing process and an excellent spectral response was observed.