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1.
V. N. Zabaev V. V. Kaplin S. I. Kuznetsov S. R. Uglov 《Physics of Particles and Nuclei》2014,45(2):508-515
Results of experiments conducted at the Tomsk synchrotron to study resonant X-ray transition radiation generated by relativistic electrons in periodic multifoil radiators are reviewed. Both the internal synchrotron beam and the external secondary electron beam from the pair magnetic γ-spectrometer with energies ranging from 300 to 900 MeV were used in the experiments. The radiators consisted of many thin amorphous foils of various materials. The generation of X-ray radiation in a compound radiator consisting of a multifoil radiator and a crystal is also studied. In this case, the resonant X-ray transition radiation generated in the multifoil radiator is diffracted in the crystal and emitted at Bragg angles, together with the parametric X-ray radiation generated in the crystal. Spectral and angular properties of the resonant X-ray transition radiation and diffracted resonant X-ray transition radiation are investigated. The ratio between the contributions from the diffracted resonant X-ray transition radiation and other types of radiation to the total coherent X-ray radiation flux generated by electrons in periodic structures and crystals is estimated. 相似文献
2.
The problem of particle creation from vacuum in a flat Robertson-Walker space-time in the presence of a varying electric field
is studied. The Klein Gordon equation is exactly solved when the scale factor is a(η)=A+Btanh(λη). The canonical method based on Bogoliubov transformation is applied. The pair creation probability and the density number
of created particles are calculated. The particular case of radiation dominated universe is considered where the total probability
is written as a Schwinger-like series. It is shown that the electric field amplifies gravitational particle creation. 相似文献
3.
《Physics Reports》2005,409(5):261-359
The features of electromagnetic processes are considered which connected with finite size of space region in which final particles (photon, electron–positron pair) are formed. The longitudinal dimension of the region is known as the formation length. If some external agent is acting on an electron while traveling this distance the emission process can be disrupted. There are different agents: multiple scattering of projectile, polarization of a medium, action of external fields, etc. The theory of radiation under influence of the multiple scattering, the Landau–Pomeranchuk–Migdal (LPM) effect, is presented. The probability of radiation is calculated with an accuracy up to “next to leading logarithm” and with the Coulomb corrections taken into account. The integral characteristics of bremsstrahlung are given, it is shown that the effective radiation length increases due to the LPM effect at high energy. The LPM effect for pair creation is also presented. The multiple scattering influences also on radiative corrections in a medium (and an external field too) including the anomalous magnetic moment of an electron and the polarization tensor as well as coherent scattering of a photon in a Coulomb field. The polarization of a medium alters the radiation probability in soft part of spectrum. Specific features of radiation from a target of finite thickness include: the boundary photon emission, interference effects for thin target, multi-photon radiation. The theory predictions are compared with experimental data obtained at SLAC and CERN SPS. For electron–positron colliding beams following items are discussed: the separation of coherent and incoherent mechanisms of radiation, the beam-size effect in bremsstrahlung, coherent radiation and mechanisms of electron–positron creation. 相似文献
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5.
The present Letter deals with consideration of high-energy electron–positron pair ionization losses in thin dielectric plate which it traverses after being emitted from substance where it is created. It is shown that in this case the Chudakov effect of reduction of pair energy losses takes place on much larger distance from its creation point than in the case of the pair motion in homogeneous infinite medium. It is demonstrated that due to transition radiation which appears during the pair emission from the substance the ratio of the pair energy losses in two plates situated on different distances from it is noticeably different from the case when the radiation is neglected. 相似文献
6.
The quantum electrodynamics(QED)in a spatially flat(1+3)-dimensional Friedmann-Lema?tre-Robertson-Walker(FLRW)space-time with a Milne-type scale factor is outlined focusing on the amplitudes of the allowed processes in the first order perturbations.The definition of the transition rates is reconsidered such that an appropriate angular behavior of the probability for creation of an electron-positron pair from a photon is obtained,which has a similar rate as the creation of a photon and an electron-positron pair from vacuum.It is shown that these processes are allowed only in the first order perturbations,since the photon emission or absorption by an electron or positron are forbidden. 相似文献
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8.
We have studied the behavior of the Feshbach-Villars equation (FV0) in comparison with the Klein-Gordon one (KG) in the problem of particle pair creation from the vacuum in an external electromagnetic field, considering two approaches: the Schwinger effective action method and the Bogoliubov transformation technique. In the first approach the vacuum to vacuum transition amplitude is calculated treating the FV0 field like a bosonic field. For the second approach, that uses canonical quantization, it is shown that the relative fields and their conjugate moments obey a commutation relation and not anticommutation one. The pair creation probability and the probability that the vacuum remains a vacuum calculated from the FV0 equation are, consequently, the same as those obtained from the KG one.Received: 12 January 2005, Revised: 24 March 2005, Published online: 4 May 2005PACS:
03.65.Ca, 03.65.Db, 03.65.Pm, 23.20.Ra 相似文献
9.
We have simulated two-dimensional classical XY-model in a microcanonical ensemble using the Monte Carlo technique. Simulations
were carried out on a square lattice having 25, 100 or 900-spins with periodic boundary conditions. The nearest neighbour
interaction potential was taken to beV(θ)=2J[1−cos100(θ/2)]. The system energy, mean square magnetization and vortex-density were calculated as functions of temperature. A sudden
change in the system energy, vortex density and mean square magnetization was observed at the first-order transition which
is associated with this choice of the nearest neighbour interaction potential. The transition temperature increases with decrease
in the system size. It is found that the creation of a vortex-antivortex pair costs more energy during the first-order transition
than the energy associated with a tightly bound vortex-antivortex pair. 相似文献
10.
We consider the process of electron-positron pair creation by an impact of ultra-intense laser beam on a highly relativistic
nucleus, with an exact account for its finite mass. It is shown that the probability rates of pair production increase tremendously
due to the nuclear recoil. Numerical calculations also show the existence of very narrow resonances in differential probability
rates of pair production, which are recognized to be Oleinik resonances, as they originate from poles of the photon propagator.
Using our exact treatment of the colliding nucleus, we analyze also the effect of dressing it by the laser field on the process
of pair creation. 相似文献
11.
A one-dimensional reaction-diffusion model consisting of two species of particles and vacancies on a ring is introduced. The number of particles in one species is conserved while in the other species it can fluctuate because of creation and annihilation of particles. It has been shown that the model undergoes a continuous phase transition from a phase where the currents of different species of particles are equal to another phase in which they are different. The total density of particles and also their currents in each phase are calculated exactly. 相似文献
12.
Stanley P. Gudder 《International Journal of Theoretical Physics》1981,20(5):383-395
It is shown that a separating or order-determining set of states on a quantum logic need not determine the expectations of observables. A formula is derived for the transition probability between states. Using this formula, it is shown that the propositions do not determine the transition probability in a certain sense. The form of the transition probability is derived for pure states on Hilbert space, dominated normal states on a von Neumann algebra, and absolutely continuous states on a measurable space. A metric is defined in terms of the transition probability. 相似文献
13.
J. Kvasnica 《Czechoslovak Journal of Physics》1969,19(12):1533-1539
The effect of the electron-positron pair creation on the intensity of radiation by an extreme relativistic plasma is studied. The degeneracy of the electron and positron gases is taken into account. It is found that the pair creation is of considerable importance for both the quantity and temperature dependence of the radiation intensity.Dedicated to Professor V. Votruba on his sixtieth birthday. 相似文献
14.
The process of pair creation by a photon in a constant and homogeneous electric field is investigated basing on the polarization operator in the field. The total probability of the process is found in a relatively simple form. At high energy the quasiclassical approximation is valid. The corrections to the standard quasiclassical approximation (SQA) are calculated. In the region of relatively low photon energies, where SQA is unapplicable, the new approximation is used. It is shown that in this energy interval the probability of pair creation by a photon in electric field exceeds essentially the corresponding probability in a magnetic field. This approach is valid at the photon energy much larger than the “vacuum” energy in electric field: ω?eE/m. For smaller photon energies the low energy approximation is developed. At ω?eE/m the found probability describes the absorption of soft photon by the particles created by an electric field. 相似文献
15.
V. V. Syshchenko N. F. Shul’ga 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2007,1(2):217-222
The transition radiation of relativistic electrons in nonuniform media is considered. Based on the equivalent photon method and the eikonal approximation in wave mechanics, a method for describing this process is proposed. For the case in which the permittivity depends on several coordinates, equations for the spectral-angular density of transition radiation are obtained. The main results obtained in the Born and eikonal approximations of the theory of transition radiation are compared. The equations obtained are used to analyze the transition radiation process for a fiberlike target. 相似文献
16.
Inelastic scattering of KeV electrons in thin films with energy losses corresponding to the infrared spectral region is discussed taking retardation into account, that is allowing for radiative modes. For sufficiently thin target films Cerenkov radiation does not play any role. Rather it turned out even for nonrelativistic electrons, that in the spectral region of negligible absorption, where for example excitation of phonons or surface phonons does not occur, the energy loss spectrum is exclusively due to the creation of transition radiation. By means of high resolution spectroscopy of electrons inelastically scattered from TiO2 films it is shown experimentally that this conclusion is indeed correct. 相似文献
17.
A.M. Perelomov 《Physics letters. A》1975,54(3):191-192
It is shown that the dynamical symmetry group of the problem of spinor particle pair creation in alternating homogeneous external field is the SO (5) group. The probability of pair creation is given by the modulus square of the matrix element of spinor representation of this group. 相似文献
18.
We show that while the statistics of static speckle patterns are generic, fluctuations in the change within speckle patterns are greatly enhanced in the localization transition. The probability distributions of the displacement of phase singularities and the standard deviations of the changes of phase and intensity with frequency shift of incident microwave radiation are given in terms of the same expression which describes the probability distribution of total transmission. This function depends only upon a single parameter, the variance of the corresponding variable. The changing statistics in the localization transition reflects the number of underlying electromagnetic modes with which the incident wave interacts. 相似文献
19.
A simple derivation is given for the leading term (n=1) in the Schwinger formula for the pair creation by a constant electric field. The same approach is applied then to the charged particle production by a charged black hole. In this case, as distinct from that of a constant electric field, the probability of the charged particle production depends essentially on the particle energy. The production rate by black holes is found in the nonrelativistic and ultrarelativistic limits. The range of values for the mass and charge of a black hole is indicated where the discussed mechanism of radiation dominates the Hawking one. 相似文献
20.
The probability of pair creation by a separable and non-local potential is considered following the Schwinger approach. It has been found that this probability is null. As a particular case, the separable δ-potential is considered and the probability is also found null. 相似文献