Formulae for the spectral and spectral-angular densities of radiation by relativistic electrons in an external nonuniform field are explored in the quasiclassical approach by taking the recoil and nondipole radiation factors into account. To compute with the formulae, a numerical method is set out. The extreme cases relevant to the radiation from an angle-type trajectory and to the constant-field approximation are considered. The results of exact and approximate calculations are presented for the radiation by high-energy electrons in the field of a single atomic string into the crystal.

The problem of increasing an efficiency of a positron source based on interaction with a target of electrons and photons of high energy is considered. It is shown that using targets of the special shape for this purpose, such as a pencil type, allows essentially (up to several times) raising an efficiency of a positron source.

In this work, the possibility of different techniques to measure real spectral-angular distributions of radiation under conditions of multiple photon generation is analyzed in dependence of experimental requirements. The technique based on Compton scattering, on narrow collimation of direct gamma-quanta beams, on pair magnetic spectrometer use and on measured opening angles of electron–positron pairs are examined. It is shown that for the measurement of photon spectral-angular distributions and photon multiplicity one can employ the narrow collimation technique. The real photon spectra within the limited emission angle may be measured with a pair magnetic spectrometer. An estimate of the multiplicity of the photons, which are registered by a total absorption spectrometer as one photon and the average energy of these photons may be obtained by measuring the opening angle of the electron–positron pairs generated by the photons in a thin converter.

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.

Coherent radiation of ultrahigh-energy (hundreds GeV) electrons in an oriented crystal is considered. It is shown that, even in conditions of essentially nondipole electron radiation in the averaged potential of an atomic chain or plane, a strong interference of radiation formed on various segments of the electron trajectory is manifested. The interference significantly affects spectral properties of radiation,

Spectral-angular and polarization properties of the gamma-radiation produced by ultrarelativistic electrons in an aligned monocrystal are investigated. An efficient source of circularly polarized gamma-quanta of high energy may be created on the ground of collimating in certain directions the coherent radiation of electrons scattered by atomic strings of a crystal.

In the motion of relativistic electrons at a small angle to one of the crystallographic axes, coherence and interference effects manifest themselves in the radiation, owing to which the gamma-radiation intensity of particles in the crystal may far exceed the intensity of radiation in amorphous medium. These effects can be used as the basis for creation of intense radiation sources with a high spectral-angular density of radiation. The intensity of electron radiation in the crystal is known to be proportional to the target thickness. Therefore, to create gamma-sources, it is advantageous to use thick crystals. However, with an increasing target thickness the average square of the angle of multiple electron scattering by atoms also increases, and this results in broadening of the angular distribution of gamma-quanta emitted, and also in the attenuation of the coherence effect of electron radiation in the crystal. Besides, in thick crystals the radiation yield can be appreciably influenced by electron energy losses and by the absorption of emitted gamma-quanta. The present paper is concerned with investigating spectral-angular distributions of 1 GeV electron radiation in thick single crystals. The main attention is here focused on the analysis of influence of the above-mentioned factors on the radiation, and to the determination of the optimum crystalline target thickness from the viewpoint of elucidating the conditions, at which the maximum spectral-angular gamma-radiation density magnitude is attained. Let us consider the radiation with the relativistic electron beam incident on the crystal along one of its crystallographic axes. In thick crystals the greater part of beam particles executes an infinite above-barrier motion with respect to crystal atom strings lying parallel to the crystallographic axis. Therefore, to the first approximation one can assume that this group of particles makes the decisive contribution to the radiation. In its above-barrier motion the electron sequentially collides with different strings of atoms. If the motion occurs at angles to the crystallographic axis, ψ, of about several critical angle values of axial channeling, ψc, the scattering and radiation of the particle from different atom strings can be considered independent [1]. In this case, the spectral-angular radiation distribution will be determined, first of all, by the special features of electron radiation in the field of a single atom row string. As a result of incoherent multiple scattering of the particle by crystal atoms, the particles are redistributed in the angles ψ. If the average scattering angle values exceed the characteristic value of the angle of relativistic electron radiation υk ~ γ, then the formation of spectral-angular distribution of radiation is significantly influenced by multiple scattering of the particle in the crystal. With due regard for the multiple scattering, the average spectral-angular radiation density can be written as