Volume capture of ultrarelativistic electrons in the axial channeling regime

Using computer simulation the volume capture effect of ultrarelativistic electrons in the axial channeling regime in crystals is investigated. The thickness, temperature and orientational dependences of the beam fraction captured in the channeling regime in the volume of the crystal are obtained.     

Anomalous passage of ultrarelativistic electrons in thick single crystals in axial channeling

The dynamics of ultrarelativistic axially channeled electrons in thick crystals is studied. It is revealed that a certain fraction of initial electrons have anomalously large dechanneling depths. It is shown also that the dechanneling depth in heavy and light crystals are comparable. In some cases, the number of channeled electrons can strongly increase at the expence of quasi-channeled electrons.

The problem of quasichanneling is also considered.     

Electromagnetic radiation of channeling electrons and positrons

General formulae for the spectral and angular distributions of radiation of relativistic channeled particles have been derived. These formulae are valid both for γ-quanta radiation and for radiation in the optical region. The problem of experimental detection of this radiation is discussed.     

The X-ray radiation of ultrarelativistic electrons in a crystal

The properties of the coherent X-ray radiation of the ultrarelativistic electrons in a crystal are considered. The total number of X-ray and resonant γ-ray quantum emitted in a crystal under diffraction conditions are calculated.     

Linear polarization of channeling radiation from axially channeled electrons

Abstract

The degree of polarization of channeling radiation emitted by axially channeled electrons has been calculated using the many-beam method. The polarization was found to be substantial, and to increase monotonically with the channeling angle. The many-beam results are compared with those obtained from the single-string approximation and are found to be significantly different.     

Large-angle channeling radiation from relativistic electrons in optically transparent crystals

In the work within the frame of quantum electrodynamics are obtained new formulae describing the large-angle photon emission from channeled electrons with taking into account of the dispersion of refractive index. Calculations based on these formulae show that the spectral and angular distributions of large-angle optical and ultraviolet radiation from planar channeled sub-GeV electrons in optically transparent crystal reflect the band structure of transverse energy levels of channeled electrons. Comparison with ordinary Cherenkov radiation spectrum reveals that channeling (depending on the beam energy) leads to sufficient change of the large-angle emission spectrum.     

“Emergency” channeling radiation due to collisions with point defects

Conditions and causes of a new effect of “emergency” channeling radiation due to collision with point defects have been obtained. Numerical calculations have shown that this effect may be considerable.     

Generation of X-ray radiation during planar channeling of relativistic electrons in crystals

A classical model of the emission of radiation by relativistic electrons in a crystal has been developed using the form of the potential maximally close to its actual form. The dynamics of electrons with energies 20–25 MeV performing channeling in crystals is simulated numerically. The generation of electromagnetic radiation that accompanies this motion has been considered. It has been shown that, in the given electron energy range, this radiation corresponds to the X-ray spectral band with characteristic photon energies of up to 40 keV. The radiation yield is estimated. The requirements to the electron beam parameters are formulated based on the results of the simulation. It has been shown that numerical simulation gives results that correlate with the analytic results obtained earlier and with the experimental data.     

Dependence of diffraction radiation on the energy of an ultrarelativistic particle

The possibility of a strong dependence of the diffraction radiation of an ultrarelativistic charged particle on its Lorentz factor is discussed. It is shown that the distribution of diffraction radiation arising when the ultrarelativistic particle flies parallel to a thin dielectric layer with finite sizes depends strongly on the Lorentz factor of the particle.     

Low mobility materials and Debye dielectric loss due to electrons

It is shown that substances which exhibit Debye type of dielectric loss due to electrons in the bulk also show very low electronic mobility. Measurements are suggested to confirm this. Relevant substances are ionic crystals with positive ions of high charge, such as oxides, and possibly certain molecular solids. In substances of the above type the band model has broken down. Relevant theoretical methods are outlined, using electron wave functions centered on the positive ions, rather than (as in previously developed methods) on their lattice sites. The perturbation giving rise to transitions between these localized states is composed of four terms, each a different kind of average of the electron-lattice interaction. One of these terms explicitly contains the effect of the localized electron on the phonon spectrum.     

Orbital angular momentum of channeling radiation from relativistic electrons in thin Si crystal

We propose to use channeling radiation (CR) from relativistic electrons as a source of high energy twisted photons in the MeV range. We calculate numerically the orbital angular momentum (OAM) of radiation produced by electrons with the energies $155÷2500$ MeV for the axial and planar channeling in the thin Si crystal. We obtain that the average OAM of CR in this case is approximately $1÷6?$ per photon with the photon energies about $1÷2$ MeV.     

Investigation of the spectral and angular distribution of gamma radiation of ultrarelativistic electrons in crystals

A technique and experimental apparatus are described for measuring the properties of radiation from relativistic electrons in crystals as a function of frequency and angle. The results of these measurements are compared with calculations and with the results obtained by other workers.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 54–62, June, 1991.     

The measured energy loss of high energy electrons in aluminum

The energy distributions of electrons of about 54, 75 and 97 Mev have been measured before and after passing through aluminum absorbers of thicknesses ranging from 0.730 to 5.574 gm/cm². The electrons were accelerated by the LINAC of the Naval Postgraduate School. The most probable energy losses agree with the theory ofBlunck andWestphal for all thicknesses; the half widths of the distributions agree with theory except for large thicknesses, where they exceed the theoretical values. These results are in contrast to those ofBreuer, which indicate systematically large half widths and most probable energy losses which are greater than theory for thicknesses greater than about 2 gm/cm². Since our data agree with those ofBreuer, the difference occurs in the treatment of the theory.     

Spectral and total intensity of radiation of relativistic electrons and positrons with planar channeling

The spectral and total intensity of radiation of relativistic electrons and positrons is considered within the framework of a Langevin approach to the theory of transit of fast charged particles across a crystal. It is shown that one of the terms of the total intensity of radiation increases exponentially rapidly along those segments of the path that are in regions in which the potential of the planar channel of the crystal has negative Gaussian curvature. Surgut State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 42–44, September, 1997.     

Parton energy loss due to synchrotron-like gluon emission

A quasiclassical theory of the synchrotron-like gluon radiation has been developed. The calculations show that the parton energy loss due to the synchrotron gluon emission may be important in the jet quenching phenomenon if the plasma instabilities generate a sufficiently strong chromomagnetic field. The resulting gluon spectrum disagrees with that obtained by Shuryak and Zahed within the Schwinger’s proper time method. The article is published in the original.     

The measured energy loss of high energy electrons in various metals

The energy distribution of electrons of about 53, 75 and 93 MeV has been measured before and after passing through Be, Sn and Gd absorbers of various thicknesses. Earlier data for Al, Cu and Pb absorbers are reviewed. The electrons were accelerated by the LINAC of the Naval Postgraduate School. The most probable energy loss and the half widths agree with the theory of Blunck and Westphal. An improved semi-empirical formula for the most probable energy loss is presented.     

Emission brightness,photon yield,and radiation losses of ultrarelativistic electrons in oriented thick crystals

The brightness E_rad/ of -radiation produced in oriented single crystals and amorphous targets of various thicknesses by electrons with E₀=900 MeV has been measured experimentally. Comparison with theoretical calculations reveals that the radiation channeled in the axial direction in diamond has the maximum brightness. The measured angular distributions and spectral composition of the radiation have been used to determine the photon yield in the cone with angle _c=0.6 mrad and it is shown that diamond has no competitors in this respect. It is concluded that the use of targets made of single crystals with Z as small as possible (diamond and beryllium) is preferable.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 8–20, June, 1991.We wish to express our sincere gratitude to Professor E. Uggeroi for providing a perfect tungsten single crystal.     

High energy electrons in the earth's radiation belts

Special experiments performed aboard the space stations Salyut-6-SoyuzProgress, Salyut-7-Soyuz T-13-Kosmos-1669, and the artificial earth satellite IK Bolgariya-1300 discovered, significant electron and positron fluxes with energies of more than decades of MeV in the earth's radiation belts. Spatial and angular characteristics of these fluxes have been studied. Study of the charge ratio of the electron-positron component has shown that it is electron-based. This indicates that in outer space near the earth some efficient mechanism capable of accelerating electrons to energies of more than decades of MeV exists.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 38–43, September, 1986.The authors consider it their pleasant duty to express gratitude to V. M. Gracev, S. V. Koldashov, A. V. Popov, and S. E. Ulin for their preparation of the equipment and conduct of the experiments.