Relativistic Electrons In Crystal Research Articles

Effect of crystal parameters and orientation on the angular distribution of diffracted transition radiation from relativistic electrons

The influence of the finiteness of the width of the total X-ray reflection region on the angular distribution of diffracted transition radiation of relativistic electrons in crystals is analyzed. Such an effect is investigated for different reflecting planes, diffracted X-ray energies, and electron beam energies and is found to be non-negligible and to substantially change the angular distributions of diffracted transition radiation under certain experimental conditions. The difference between the reflectivity and the δ function is shown to distort the angular distribution of the detected radiation and to limit the possibility of using this type of radiation to diagnose the parameters of beams of relativistic electrons and positrons with energies greater than 50 GeV.

Spontaneous Emission during the Channeling of Relativistic Electrons in Crystals with a Hexagonal Structure

Spontaneous Emission during the Channeling of Relativistic Electrons in Crystals with a Hexagonal Structure

CHARGE-NUMBER OF PULSES-CONVERTER

It is described the charge-number of pulses-converter, which was successfully applied in the ”Program-apparatus complex for investigation of gamma- and X-rays radiations, generated by relativistic electrons in crystals” [1] at Kharkiv linear electron accelerators. This device is in the condition for high energy electron (positron) beam charge measurements with accuracy 2·10−10 C and current measurements in the range of 10−10...10−8 A.

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.

Influence of multiple scattering of relativistic electrons on the linewidth of Parametric X-ray Radiation produced in the extremely Bragg geometry in the absence of photoabsorption

The multiple scattering effect on the linewidth of backward Parametric X-ray Radiation (PXR) produced in the extremely Bragg geometry by low energy relativistic electrons traversing a single crystal is discussed. It is shown that there are conditions when the influence of photoabsorption on the linewidth can be neglected, and only the multiple scattering process of relativistic electrons in crystals leads to the PXR lines broadening. Based on obtained theoretical and numerical results for the linewidth broadening caused by multiple scattering of 30 and 50MeV relativistic electrons in a Si crystal of various thicknesses, an experiment could be performed to help in revealing the scattering effect on the PXR lines in the absence of photoabsorption. This leads to more accurate understanding of the influence of scattering process on the linewidth of backward PXR and helps to better construct a table-top narrow bandwidth X-ray source for both scientific and industrial applications.

Frequency-angular characteristics of quasicharacteristic radiation in the case of plane channeling of relativistic electrons in crystals

In this paper, a theoretical study of the frequency-angular characteristics of short-wavelength quasicharacteristic radiation is presented. This radiation is produced as a result of transitions between the energy levels of transverse motion in the case of plane channeling of relativistic electrons in various crystals. Detailed numerical analysis shows that short-wavelength radiation, the parameters of which remain unchanged in a broad range of particle energies, exists at small angles in the domain of existence of the normal complex Doppler effect.

Parametric channeling and collapse of beams of charged particles with internal structure in crystals: 2. Parametric processes during channeling of atomic ions, nuclei, and relativistic electrons in crystals

Features of parametric effects during channeling of atomic ions, nuclei, and relativistic electrons (positrons) in crystals were considered. It was shown that parametric coupling between ion channeling states in the field of crystal axes and planes and electronic states in the ion volume leads to the possibility of “parametric collapse” of the beam, i.e., a decrease in the oscillation amplitude of the atomic ion in the channel due to periodic transfer of the ion oscillation energy to the inner electron of the atom. The same effect can be used to cool beams due to energy transfer to intrinsic nuclear states with low energy levels. It was shown that parametric cooling of beams with a decrease in the transverse energy can also occur during axial channeling of relativistic electron beams. This process results from the parametric coupling between channeling states, which are caused by the particle charge and electron spin states in an effective magnetic field induced in the moving coordinate system.

Coherent x radiation induced by relativistic electrons in crystals

We present the results of a theoretical study of coherent x radiation induced by relativistic electrons in crystals for observation angles exceeding ${\ensuremath{\gamma}}^{\ensuremath{-}1},$ where $\ensuremath{\gamma}$ is the projectile Lorentz factor. The assumption for the process includes both elastic and inelastic radiation mechanisms. The results were compared with available experimental data.

Study of incoherent x-radiation induced by relativistic electrons in crystals

Features of incoherent x-ray radiation, produced by relativistic electrons with energy of several tens of MeV in crystals, are studied for observation angles exceeding ${\ensuremath{\gamma}}^{\ensuremath{-}1}$ (\ensuremath{\gamma} is the projectile Lorentz factor) and for all possible momentum transfer. It is shown that the fivefold cross section has a pronounced structure, with sharp maxima and a minimum. A Monte Carlo procedure is developed to obtain a threefold cross section and, then, contributions of different radiation mechanisms are analyzed. The results of numerical integration are compared with experimental ones, and a good agreement between them is verified. The obtained results can be used both in experimental investigations dealing with interaction of charged particle beams with crystals, and to optimize parameters of x-ray sources based on the coherent x-radiation process.

Incoherent X-radiation produced by relativistic electrons in crystals

Differential and integral features of incoherent X-radiation, induced by relativistic electrons in crystals, are studied for observation angles θγ several times greater than γ-1, where γ is the projectile Lorentz factor. The existence of sharp maxima and a minimum of the five-folded incoherent differential cross-section as a function of the final electron angles, and a dip minimum when the cross-section is taken as a function of the photon energies, is demonstrated. At near backward observation angles the three-folded cross-section shows a maximum in the region of several keV photon energies. The obtained results allow us to optimize the conditions for coincidence experiments, minimizing the incoherent contribution to the total radiation yield, and helping to analyse results of finite-size detector experiments with crystal targets.

Simulating spectrum and polarization of coherent radiation by relativistic electrons in crystals

In the paper we attract attention to the fact that the inclusion of the actual dynamics of a particle moving inside a crystal at a small angle to one of its axes leads to a considerable distortion of spectrum and polarization characteristics of the coherent radiation obtained assuming the trajectory to be a straight line. It is essential that not only the radiation intensity but also the interference pattern of the radiation process undergo changes. That is important in quantitative analysis of measured data.

Axial channeling of relativistic electrons in crystals as a source for positron production

In the framework of studies of positron sources dedicated to linear colliders, crystals are considered as photon radiators in association with thin amorphous converters or as compact positron sources where photon production and pair creation occur in the same medium. The main features of such sources in comparison with conventional amorphous sources are described. Taking linear collider requirements for such sources, a crystal converter suited for the Japanese Linear Collider (JLC) is considered. Limitations caused by radiation damage are mentioned and indications on critical fluences are given. A proof-of-principle experiment has been undertaken in Orsay, observing radiation enhancement in a tungsten crystal oriented along the 〈111〉 axis and submitted to a 2 GeV electron beam. The main results are reported.

Effective positron source based on coherent radiation of relativistic electrons in crystal

A two stage positron source with a crystalline radiator is considered. The dependence of the positron yield on the primary electron beam divergence and the radiator materials is studied. At the high energy, the radiator from light elements provides a higher positron yield but needs beams with a less divergence.

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 γ 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.

Experimental study of the albedo of a beam of ? rays produced by ultrarelativistic electrons

A study has been carried out of the spectral dependence of γ-radiation scattered from targets irradiated with beams of γ rays produced by relativistic electrons in crystals. It is shown that the change in the spectral composition of the beam of γ rays incident on the target changes considerably the spectral properties of the scattered radiation. The spectra of the scattered radiation are studied as a function of the thickness and atomic number of the scatterer. It is shown that the atomic number of the scattering material can be determined from the ratio of the spectral components of the scattered radiation.

On the new type of radiation in channeling relativistic electrons in crystal

On the new type of radiation in channeling relativistic electrons in crystal

Computer Simulation of the Volume Capture Effect for Relativistic Electrons in Crystals

Computer Simulation of the Volume Capture Effect for Relativistic Electrons in Crystals

Molecular‐type channeling of relativistic electrons in crystals

AbstractChanneling of relativistic electrons in 〈110〉 direction in a diamond crystal and the channeling radiation spectra are investigated using computer simulation by the binary collision model and using the model of a continuum potential of the atomic rows. In a computer experiment the atomic‐ and molecular‐type states of channeled electrons are revealed, and the orientational dependence of the electron trapping probability in these states is obtained. The peculiarities revealed of the angular distributions and radiation spectra of electrons in the molecular‐type states allow to discover these states in the experiment.