نشریه پژوهش های نوین فیزیک
سال چهارم شماره 1 (پیاپی 6، بهار و تابستان 1398)

Recently, generation of terahertz radiation has become one of the most attractive topics in varieties of fields of physics. In the present paper, the two-section periodical circular waveguide excited by electron beam as a terahertz radiation source is investigated. By choosing the suitable parameters of system, the frequency of the propagating wave in second section (diffraction radiation frequency) is twice the frequency of first section (bunching frequency). The results show that with 20 kV beam voltage, the coherent diffraction radiation with frequency close to .036 THz can be generated. Since, the starting beam current density reduces, it is anticipated that this structure form an important part of future THz systems.

Within Weber’s approach, we study the classical and quantum scalar field theory in the Schwarzschild metric. By employing the localized coordinates and the Bateman – Caldirola – Kanai method, we find a Lagrangian density of the scalar fields from the deformed motion equation of them. Also, we show that approximated theory has an exact established solution and Green’s function by replacement the ordinary field’s mass with the u-mass. We know that the new fields do not obey the second quantization relation. So the classical and quantum scalar fields have different treatments in Weber’s method. Thus, we must admit a new background field for quantum cases. Locally homeomorphism between pseudo Riemannchr('39')s manifold and Minkowski one is considered.

Environmental monitoring, which is an inseparable component of nuclear safety, is always important. The need for regular, accurate and qualified implementation is essential. The gamma spectrometry method is widely used for the detection and measurement of gamma emitting radionuclides in natural samples. In the gamma spectrometry method, like all methods of measurement, the determination of measurement uncertainty is evident. The aim of this study is to measure the gamma-ray radionuclide activity of the soil sample and the correct associated uncertainty. A soil sample in a cylindrical container and weighing 243 grams was used based on the 661 keV peak of cesium and a high-purity germanium detector (80% relative efficiency) for calculations. According to the counting of 72000 second of the soil sample, the amount of cesium activity was 482 Becquerel. Also, the uncertainty of the above activity measurements was calculated 33.4 Becquerels. The results of this study indicate that the measurement of activity of gamma emitting radionuclide with relative uncertainty of 6.9% indicates the high reliability of the results. Also in the total uncertainty, the counting and efficiency uncertainty make the main contribution.

In this work, we determine the non-perturbative fragmentation function (FF) of B-mesons (meson including a bottom quark flavor), phenomenologically, at next-to-leading order QCD perturbation theory using data from electron-positron annihilation. In this regard, we apply all current experimental data from OPAL, ALEPH, SLD2002 and DELPHI collaborations. We also apply the Hessian method to calculate the error in determination of FFs. As an application, using our extracted results we shall make our predictions for energy distribution of B-mesons produced through top quark decay. Study of the B-meson energy spectrum can be considered as a convenient channel to search for the properties of top quarks at CERN.

In this paper, the electron energy gain and its relativistic dynamics in an ion-channel formed due to the laser pulse and under influence of the channel space-charge field and heliacal wiggler as well as the external magnetic field have been investigated. The equations for investigation of the electron dynamics are the tree-dimension Lorentz equations. For analytical analysis of the obtained equations, a three-dimension single particle code is used as well. The electron energy gain and the relativistic electron dynamics drastically are affected by the ion-channel potential and the helical wiggler and external uniform magnetic fields. The results of this paper can be significant in the selection of the appropriate parameters for plasma-based accelerators design.

Cr–doped SnO2 nanoparticles (SnO2: Cr NPs) synthesized by sol-gel process. Influence of structural parameters, intrinsic and extrinsic defects of NPs on physical properties and photocatalytic performance of nanoparticles were investigated by various analytical techniques. X-ray photoelectron spectra revealed that Cr ions incorporated in SnO2 lattice with chemical state of +3. The X-ray diffraction analysis disclosed that crystallite size and lattice parameters reduced slightly while dislocation density increased by Cr doping. The isotropic (anisotropic) lattice strain, crystallite size, young modulus, lattice deformation stress, and deformation energy density of nanoparticles were estimated by XRD line profile analysis using modified Williamson–Hall method assuming the isotropic strain model (ISM), anisotropic strain model (ASM) and energy density model (EDM). The tensile strain of SnO2 reduced by Cr doping and converted to compressive strain for higher doping level. Transmission Electron Microscopy (TEM) micrographs confirmed that average particle size reduces by Cr doping. Ferromagnetic behavior was observed in low level Cr-doped SnO2 NPs at room temperature and saturation magnetization decreased as doping level to 5 mol% increased. Band gap narrowing, mid-gap state absorption in UV-Vis spectra, and transition from tensile to compressive strain proved that the oxygen vacancies/extrinsic defects (Cr 2p) and microstrain play an important role in weak ferromagnetism and enhanced photodegradation of Cr doped SnO2 nanoparticles against rhodamine B (RhB) and methylene blue (MB) dyes.

The Chiral Magnetic Effect (CME) is a phenomenon in which, a chiral chemical potential in an external magnetic field lead to an electric current along the magnetic field. This phenomenon has been observed in systems containing quark-gluon plasma and recently in systems concerned with condensed matter physics. Interactions in these systems are strong. Therefore, the best approach to analyzing this phenomenon is gauge/gravity duality which is a good tool for studying systems with strong interactions. Since, Lorentz symmetry does not existed in some condensed matter models, here, the chiral magnetic effect in non-relativistic systems is studied by introducing a suitable gravitational dualism. We will see Lorentz symmetry is broken and non-relativistic z=2 Schrodinger symmetry appears which is realized by Anti-de-Sitter-Schwarzschild black hole. In our Holographic model, system’s properties are in a good agreement with the experimental result of strange metals at very low temperature. What is really important is that, the chiral electric current in our model for a non-relativistic system which is dual to strange metal is half of what is obtained in relativistic Anti-de-Sitter space-time before.