مجله پژوهش فیزیک ایران
سال بیست و یکم شماره 4 (زمستان 1400)

In this paper, the design and construction process of a traveling wave electron linear accelerator is presented briefly. The machine consists of an electron gun followed by a prebuncher, a traveling wave buncher, an accelerating tube and the diagnostics instruments. Solenoid magnets provide the beam focusing. A klystron has been used as the RF power source. The linac components are controlled and monitored by a comprehensive control system. All the sub systems of this accelerator are designed and developed based on the domestic technology. The output beam has a maximum energy of 4.5 MeV. The beam parameters like energy, intensity, transverse size and emittance are measurable and tunable. The IPM Linac is a unique tool for experimental R&D in accelerator and beam physics in Iran.

In this paper, we investigate optical properties of silver ellipsoid nanostructures (SENs) by means of discrete dipole approximation (DDA), when these nanoparticles are embedded into the water. Absorption, scattering and extinction cross-sections of the SENs were calculated by change of incident wavelength in visible and near infrared region. Moreover, height, wavelength and full width at half maximum (FWHM) of extinction cross-section peaks (due to plasmon resonances) were studied by change of nanostructure's size and dielectric constant of medium. Our results show that, there are only two peaks of transverse dipole and longitudinal dipole modes in this spectrum.

In this study, we investigate the trajectory of magnetic nanoparticle flowing through a microvessel in the presence of cylindrical magnet. By using the equation of motion of particle in the presence of magnetic and fluidic forces, the motion trajectory of magnetic particle in the microvessel is calculated. Our numerical results show that the probability of trapping magnetic particles in the straight microvessel is a function of the intensity of the magnetic field, particle radius, particle magnetization, and diameter of vessel. In this study, we investigate the effect of particle radius, magnet magnetization, particle saturation magnetization and vessel radius on the trajectory of magnetic nanoparticle flowing through the straight vessel. The results show that with increasing particle radius, magnet magnetization, particle saturation magnetization and also with decreasing vessel radius, the probability of trapping a floating particle in the channel increases

In this paper, we report on random lasing emission from colloidal solutions of graphitic carbon nitride (g-C3N4) microstructures. The g-C3N4 microstructures are dispersed in rhodamine B (RhB) dye solution to provide the necessary optical feedback via light multi-scattering events. RhB molecules provide optical gain via stimulated emission process under intense optical pumping. It is experimentally demonstrated that random lasing action occurs in the colloidal solution composed of dye and g-C3N4 microstructures, after a specific threshold. We study the pump dependent behavior of the proposed system. Since only amplified spontaneous emission is achieved from the solution of RhB dye without g-C3N4 microstructures, it is demonstrated that the existence of g-C3N4 microstructures has a key role in the observation of random lasing emission. Finally, we change the concentration of g-C3N4 microstructures and observe that the output intensity increases and the lasing threshold decreases by increasing the concentration of g-C3N4 microstructures. It is then verified that g-C3N4 microstructures can be a good candidate for the scattering medium in random lasers and the essential optical feedback for realizing random lasing emission is provided by light multi-scattering from g-C3N4 microstructures.

In the present study, we have systematically studied the role of surface energy coefficient as well as temperature dependence in the fusion hindrance phenomenon of the heavy-ion reactions using the proximity potential formalism. To this end, we have performed the calculations of the interaction potential using the original proximity potential 1977 (Prox. 77) and the fusion cross sections are calculated based on the coupled-channels (CC) approach. The considered fusion systems are including the heavy-ion reactions 11B+197Au, 12C+198Pt, 16O+208Pb, 28Si + 64Ni, 28Si + 94Mo, 58Ni+58Ni, 32S+89Y,34S+89Y, 12C+204Pb and 36S + 64Ni with conditions of Q <0 and charge product of the participant nuclei 392≤ Z1Z2 ≤784. Our preliminary calculations show the Prox. 77 model predicts the theoretical values ​​of the fusion cross-sections less than the corresponding experimental data especially in the energy regions below the fusion barrier. However, the imposing of the mentioned physical effects increases the calculated values of the fusion cross sections and thus improves their agreement with the experimental cross sections for the selected reactions. In addition, by considering the energy dependence on the surface energy constant γ0 of the proximity formalism at the low energy region we are able to reproduce well the fusion cross sections, the astrophysical factor S(E) as well as the logarithmic derivative L(E) in these regions.‎

In this paper, the electron acceleration by plasma wave in IFEL mechanism in the presence of a quadruple magnetic field and ion channel guiding effects has been investigated both analytically and numerically. The results illustrate that the increasing of the quadruple wiggler amplitude and wavelength up to an optimum value has considerable effects on the electron acceleration and its relativistic dynamics in laser ion channel. It was found that in the presence the optimum values of quadruple wiggler amplitude and wavelength, the electron energy gain increases more than 90% than that obtained in the absence of the wiggler. Moreover, the numerical simulations reveal that if the electrons are thrown with higher initial kinetic energy into the wiggler field, they can longer remain in the acceleration phase of the plasma wave and gain more energy from the wave. Therefore, it turns out that, in a laser-plasma accelerator, the electron acceleration and its relativistic dynamics can be tuned by the wiggler field strength, wiggler wavelength, and initial kinetic energy of electrons. The favorable results of studies in this field can be promising for the new generation of the laser-plasma accelerators based on the wiggler structures.

In the present work, the fully differential cross section of atomic helium ionization by protons impact at high energy ranges is calculated. The calculations of the fully differential cross section have been performed by using the three-body formalism in the first order Born-Faddeev approximation with an active electron model and four body formalism with the first Born approximation. In order to investigate the collision dynamics accurately, the first order Born-Faddeev approximation has been performed by using the single parameter and Hartree Fock as single-electron wave functions and in the first order Born approximation, the two-electron wave functions of Hylleraas and Silverman are used with considering the electron correlation. The fully differential cross sections at different ejected electron energies and momentum transfers are compared with the available experiment and theoretical results. The results show that the effects of electronic correlation are considerable at high impact energy range and ionization process.‎

The nucleon-nucleon correlations of asymmetric nuclear matter (ASM) in the 3S1-3D1 and the 3P2-3F2 states with the AV18 and the AV’6 potentials are studied in the lowest order constrained variational (LOCV) method. In these computations, the tensor (or the spin-orbit) correlations are considered in the 3S1-3D1 (3P2-3F2) state. The energy, as well as the healing distance of the ASM in the mentioned states, are reported. It is demonstrated that by decreasing the proton to neutron ratio, the non-central correlations (healing distances) of the coupled states grow. It is shown that the ASM non-central correlations and energies in the 3P2-3F2 state are more sensitive to the interaction than those of 3S1-3D1 state.

In this research, squeezing fragility due to thermal bath, in quantum squeezed state generation, is simulated. For this purpose, single mode dissipative cavity with non-zero second-order susceptibility is used. Cavity nonlinear medium is driving by laser pump with known frequency, and pairs of identical photons are created, with one-half frequency of driving pump. This process known as degenerate parametric down conversion. In the absence of any dissipation, simulation shows linear time dependent squeezing parameter, which is in agreement with theoretical results. In two photon loss of cavity in contact with cold reservoir, competition between gain and two photon loss, results in stable squeezing of initial vacuum, in steady state of system. At the end, has been shown that, non-zero thermal reservoir, omits the squeezing and leads the final cavity field to the thermal mixture of Fock states.

Cavity solitons as part of dissipative localized structures have been of great interest. In cavity, there must be the double balance between dispersion phenomenon and nonlinear phenomena and at the same time the cavity losses are made up for by pumping continuous-wave coherent driving which leads to the formation of  Spatio-temporal soliton. In previous studies z direction has neglected in the cavity. By taking into account of this direction the new type of solitons named “phase soliton” is introduced. In this paper, we studied the ring cavity in more detail and the intraction of duble phase soliton. We find out, switching  ON and OFF process of phase soliton. Also   the optimal conditions for switching ON/OFF was determined.

In this article we show that a single transparent wedge or a plate with a wedge part can be used as a very simple and useful interferometer with numerous applications. This interferometer permits to modulate phase distribution on interference fringes to evaluate quantitatively the parallelism of a light beam and aberration of a wavefront, to specify the spectral line shape in a wide range, to measure the light wavelength and refractive indices of solids and liquids. In addition, it provides suitable beams for holographic study of phase objects and fabrication of diffraction gratings.

In this paper, the decay of the  meson into two vector mesons  and  is investigated.The first observation of the decay was reported in 2017 by LHCb collaboration, they have obtained the value of B () = (5. 01 ± 053 ± 0.27 ± 0.06)×10-4. In this study, the Feynman diagram of  decay is drawn based on the standard model. In particular this diagram shows that the decay consists of tree-exchange internal w-emission graph and penguin- suppressed graph. The coefficients of a2, a3, a5 and a7 are calculated in the NLO scale. The branching ratio is calculated using the QCD factorization method, numerical values in the NLO (at mb scale) scheme is 5.33×10-4, for which are in good agreement with the experimental results. The more calculations accuracy increases, the b quark mass scales come down corresponding to that. The best answer close to the experimental value is in NLO scheme at mb scale of QCDF approach.‎

Recently, the production of high-speed ions has attracted the attention of researchers because of the important applications in fusion and medicine applications. In this study, the production of energetic ions of tens of giga electron-volts in the interaction of a femtosecond laser with a very thin layer of plasma has been investigated using Particle in Cell LIPIC ++ Code. Access to such energetic ions become possible by using a two color laser beam including the first and third harmonics and by means of the proper selection of many effective factors such as the ratio of intensities and relative phases of the two harmonics, material, charge and thickness of the target, angle of the incident pulse , the duration and intensity of the laser pulse, and the density of the plasma. The intensity of the laser is not relatively high in respect to the rate of acceleration, and it can be hoped that the proposed conditions will be appropriate way to produce highly energetic ions with energies greater than 35 GeV.

In this paper we will consider cosmological implications of the Rastall theory with a non-minimal coupling with baryonic matter fields. In Rastall theory, the matter energy-momentum tensor is not conserved and the non-conservation is related to the curvature. We will generalize this relation to become dependent on both curvature and matter fields. Cosmology of the model shows more matter abundance compared to the model. We will show that the dynamical system of the model is the same as with an additional degree of freedom.

Oscillations in various structures of the solar atmosphere, such as transverse (kink) oscillations of coronal loops, can be used in seismology. Transvers kink oscillations of coronal loops are often accompanied by solar flares. Despite the intensive study of kink oscillations of coronal loops in recent years, the excitation mechanism of these oscillations are still not known. In this paper, we aim to clarify the excitation mechanisms of transverse oscillations of coronal loops. For this purpose, first 458 oscillation events were identified by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) during its first ten years (2010–2019) with the use of the Helioviewer, JHelioviewer and Heliophysics Events Knowledgebase (HEK). Then, the association of these oscillation events with probable mechanism for exciting the kink oscillations such as flares, lower coronal eruptions and plasma ejections, and coronal mass ejections bursts were listed. Finally, about 138 suitable kink oscillations out of 485 oscillations with high-amplitude, long oscillation period and visible through the naked eye that were accompanied with other probable excitation mechanism of kink oscillations, were selected. This statistical analysis of the transverse oscillation coronal loops showed that that 102 of these 138 oscillation events (74 %) were associated with lower coronal eruptions or plasma ejections. About 38 oscillations out of 138 transverse oscillations (27.5%) were associated with coronal mass ejections/eruption. Also, 65 events (47 %) were associated with flares. The required speed of hypothetical drivers of transverse oscillations were calculated. The magnitude values of calculated speeds for shock wave of flares were found to be lower than 500±100 km/s in 87% of the cases. Also, the magnitude values of speeds for lower coronal mass eruption/ejection were obtained to be lower than 500±125 km/s in 94% of the cases. The magnitude values of these speeds are acceptable for lower coronal mass eruption/ejection. But, such low speeds do not favor the association of the oscillation excitation with a shock wave of flares, as usually assumed. Also, statistical analysis of start time and time difference of hypothetical drivers of transverse oscillations showed that there is no clear correlation between them. The results of this study indicated that shock wave of flares cannot be the main cause of transverse oscillations of coronal loops. So, this analysis shows that the most probable excitation mechanism of the kink oscillations of coronal loops are eruptions or plasma ejections rather than the blast shock waves ignited by flares. ‎

The study of many-body quantum systems, that fail to thermalize in the presence of disorder, has recently attracted lots of interests. This is due to the appearance of the many-body localized phase and breakdown of eigenstate thermalization hypothesis in such systems which can be described by the local integrals of motion. In this paper, we consider a disordered spin chain in the many-body localized phase and try to study the dynamics of entanglement generation in this system using the local integrals of motion. To this end, we, first, solve the non-interacting system analytically to describe the mechanism of entanglement generation for different kinds of initial states, exactly. Then, we generalize this approach to the interacting system to learn the dynamics of entanglement generation. Finally, we discuss the physical meaning of different behaviors in the dynamics of entanglement generation in the presence and absence of interaction.‎

In this study, an efficient and compact optical device for slowing light in corrugated photonic crystals with different corrugation patterns are discussed. The proposed structure shows relatively large group delay with wide bandwidth and approximately zero group velocity dispersion in near-infrared region. Also, due to the zero group velocity dispersion applied on transmitted pulse, high quality pulse can be obtained by using this approach. For comparison, three different photonic crystal structures containing triangular, sinusoidal and graded sinusoidal corrugation patterns were investigated. The group index as much as 5 with the bandwidth about 50 nm is achieved in the sinusoidal corrugated photonic crystal with 8 μm length. This slow-light structure is very promising for application in quantum memories.

Bound state equations are mostly solved in partial-wave truncated basis. In partial-wave method, we need to consider many partial waves to reach the accurate results. In this paper, we avoid partial-wave decompositions and directly work with vector variables to solve homogeneous and inhomogeneous Lippmann-Schwinger equations. We study binding energies of deuteron and atomic hydrogen using three-dimensional approach.

Using the density-dependent equation of states to describe the matter of rotating neutron stars, we construct equilibrium configurations of rotating neutron stars. The interaction between baryons is described by exchanging the scalar and vector mesons in the relativistic mean-field theory. The mesons coupling coefficients are functions of the environmental density. The sequence of equilibrium states is calculated for the four frequencies observed for rotating neutron stars namely, 25, 317, 716, and 1122 Hz. These sequences are constrained by static, Keplerian (mass-shedding sequence), and secular axisymmetric instability sequences. This allows the radius and mass range of the stars will be obtained in each of the models. We can also calculate the parameters of the fastest rotating star described by each model.

Potential energy surface was calculated for the ground electronic state of the triatomic ion ClO2− using the coupled-cluster method CCSD(T). Calculations were carried out for 1200 points on the potential energy surface, and the calculated points were fitted to the potential energy expression in terms of the internal coordinates, from which the quadratic, cubic and quartic force fields were determined. Using the second-order rovibrational perturbation theory, harmonic vibrational frequencies, anharmonicity constants and several other spectroscopic parameters were calculated, and accurate fundamental vibrational frequencies were obtained. Also, the energies of 30 lowest vibrational levels were calculated using the anharmonicity constants.

In this research, by assuming that the vacuum electric field fluctuations can convert a molecule (or an atom) into an oscillating electric dipole, the interaction potential of the two atoms or two non-polar molecules is calculated in terms of the molecular polarizabilities and the distance between them. Considering the net electric field at the position of a molecule as a sum of the vacuum electric field and the electric field due to the induced electric dipole of the other molecule, and substituting in the quadratic stark shift formula, the interaction potential of the two molecules is related to the vacuum electric field correlation function. By writing the interaction potential in terms of the imaginary parts of vector potential Green function tensor components (via the fluctuation- dissipation theorem and Kubo’s formula in statistical mechanics) and computing the required Green function components, the interaction potential between the two molecules is evaluated. The small and large distances limits of the general formula investigated and the consistencies with the previous works are shown.‎

Arsenene is one of the members of a large group of two-dimensional structures that in the present project, we have investigated the single layer structure and its nanoribbons based on density functional theory. In this study, after calculating the single layer band structure, we discussed the effect of width on the band structure of nanoribbon from the angle of quantum limiting phenomenon. The results show the different effect of quantum limiting phenomenon on different points of each band in the band structure, which is the cause of indirect-direct gap transition due to the reduction of the width of armchair nanoribbon. Also, the electrical conductance properties of arsenene single layer have been obtained by calculating the mobility of load carriers and the effect of uniaxial strain of crystalline structure on them has been investigated. In order to investigate the mobility, crystalline structure defects have been neglected and only phonon dispersion is considered based on Takagi relationship. In this process, the focus is not on the quantitative accuracy of the obtained values for the mobility of load carriers and the existing anisotropy between mobility in the two directions of armchair and zigzag has been the focus of the discussion. The results of the calculations show a significant anisotropy of mobility in the two directions of armchair and zigzag and the effect of uniaxial strain of crystal structure on it. Also, a significant difference between the mobility of electrons and holes in the direction of armchair is one of the key results.

In this study, we have considered time dependent evolution of advection dominated accretion flow (ADAF) in the presence of the toroidal magnetic field and radial viscosity. We have used time-dependent self-similar solutions for solving the 1D MHD equations in the spherical coordinates in the equatorial plane () and we have neglected terms with any θ and φ dependence. While the azimuthal viscosity υ as the turbulence factor in transporting the angular momentum and α-prescription for kinematic coefficient of viscosity is used in the most previous studies, recent studies show the disc structure can also be affected by the radial viscosity υr. In this work, we have assumed that the ratio is a dimensionless parameter 𝜉. We use ξ and β variables as free parameters to consider the effects of magnetic field and radial viscosity. The solutions indicate a transonic point in the accretion flow. This point approaches to outward by increasing the magnetic field and radial viscosity. Also, by adding strength of the magnetic field, the radial-velocity of the disc decreases and the disc compresses. Also, the flow is sub-Keplerian at all radii. The 𝜉 parameter has the same behavior in the inner and intermediate regions of the flow but in the outward of the flow, by adding the 𝜉 parameter, accretion rate increases and hence, it is expected that the disc has a shorter lifetime with radial viscosity.

Proton therapy is one of the best methods of treatment for liver cancer. In this research, the main parts of proton therapy system, with passive scattering nozzle, including range-modulating wheel, energy-compensated contoured scatterer and collimators were simulated. Then the proton absorbed dose in healthy and tumoral tissues was calculated by simulating the proton therapy of liver tumors. Furthermore the secondary neutron dose, that increases the risk of secondary cancers, was calculated. For this purpose, the neutron equivalent absorbed dose in tumor and healthy tissues were calculated. Furthermore, the MIRD phantom was located in front of the output of the proton therapy system. By simulating the proton therapy for tumor in depth of 11 cm in the liver with mean source energy of 200 MeV, the absorbed dose of proton in tumor estimated as 3.32 × 10-12 Gy/particle that is 7.26 times more than proton dose in healthy parts of liver. This ratio showed that tumor absorbs the maximum dose, while the healthy tissue absorbs the minimum dose. In the next step, the same procedure was done with mean source energy of 180 MeV for tumor in depth of 6 Cm. According to the results, the proton absorbed dose in tumor was 1.94 × 10-12 Gy/particle that is 9 times more than proton absorbed dose in healthy tissue. Also the maximum neutron equivalent absorbed dose in healthy tissue is of the order of 10-14 Sv that can be ignorable in comparison with proton treatment effects of proton therapy.

Quantum theory sets a bound on the speed of quantum evolution. The shortest time needed for a quantm system to evolve from an initial state to the target state is known as the quantum speed limit time. The study of this time in open and closed quantum systems has been the subject of much work in quantum information theory. Quantum speed limit time is inversely related to the evolution rate of a quantum process. This relation is such that the speed of evolution decreases with increasing quantum speed limit time and vice versa. In this work we study the QSL time for the case in which a qubit interacts with a quantum critical environment. We choose the environment to be an Ising spin chain in a transverse field. It is observed that for the quantum speed limit time has a direct relation with quantum coherence of the initial state of the system. We will also study the effect of perturbation coupling on quantum speed limit time. It is observed that the quantum speed limit time decreases with increasing the coupling parameter. It is also observed that the quantum speed limit time decreases with increasing the number of spin in spin chain.