Al-Omari M. The features of parametric X-ray radiation and ionization of atoms at the propagation of high-energy electrons in crystals.

For studying the spectral-angular characteristics of parametric X-ray radiation (PXR) with the propagation of high-energy electrons with energy of 7 MeV in crystals based on the experimental setup «Röntgen- 1», the method of excitation and registration of PXR in the geometry of reverse scattering, in particular in the field of observation angles, was developed and worked out. 150°–180° relative to the direction of propagation of the electron beam. This allowed to provide a higher signal level of 1–3% of the total radiation background level, which is sufficient for reliable registration of the PXR spectra, with the appropriate choice of accumulation time in the registration channel. In order to increase the intensity of PXR, it is theoretically provided for the possibility of narrowing the PXR cone and the increase in the angular density of PXR in the propagation of relativistic electrons in thin crystals in the region of small angles of slipping the electron beam relative to the target's surface. The spectral-angular distributions of the PXR intensity were experimentally determined by the propagation of high-energy electrons in monocrystalline silicon and high-oriented pyrolytic graphite (HOPG) in the geometry of the backward registration. It was found that the angular orientation of the intensity of the maxima (220) Si and (002) HOPG contains two symmetric maxima, which represent the cross section of the cone of the PXR perpendicular to the axis of the cone plane. It has been experimentally shown that when propagation of a beam of high-energy electrons in powder samples of a diamond with crystallite sizes d = 0.3–42 μm, at the backward of registration (θ = 151°) the ratio of the intensities of the PXR (111) and (220) maxima decreases with increasing diameters of diamond crystallites. In particular, in the transition from particles with a diameter d = 0.3 microns to particles d = 6 microns, this reduction is 1.9 times. Under the condition of excitation KαL1 spectra of the Ti, V, and Cr by electron beams (25 keV), experimentally established that the decrease in the relative intensity of the χ = I(3P)/I(1P) du to the transition from metals to the corresponding oxides, it is in the 1.6–1.9 times. It is shown that in the vanadium oxides in the V2O3 – VO2 – V2O5 series, the growth of an effective positive charge of the atom V is accompanied by a monotonous decrease in relative intensity χ from 2.4 to 1.8. And also offered a model of the effect of reducing the relative intensity in the I(3P)/I(1P) in KαL1 spectra. At the excitation of KαL1, KαL2 and KαL3, spectra Al by electrons in the energy range 4.5–100 keV experimentally determined the probability of formation of two (P2) and three (P3) additional 2р vacancies in ionization of 1s shell. Comparison of these values with the values calculated in the model of independent emission of 2р electrons due to the (shake–off) SO process, it show that for the metal Al compering with the semiconductor of silicon the magnitude P2/P2(SO) is 1.2 times less and the magnitude P3/P3(SO) is 1.7 times less, respectively.