ISSN 1063-7850, Technical Physics Letters, 2006, Vol. 32, No. 5, pp. 392–395. © Pleiades Publishing, Inc., 2006. Original Russian Text © V.G. Baryshevsky, K.G. Batrakov, I.D. Feranchuk, A.O. Grubich, A.A. Gurinovich, A.S. Lobko, A.A. Rouba, P.F. Safronov, V.I. Stolyarsky, B.A. Tarnopol- sky, A.P. Ulyanenkov, 2006, published in Pis’ma v Zhurnal Tekhnicheskoœ Fiziki, 2006, Vol. 32, No. 9, pp. 50–57. 392 The parametric X-ray radiation (PXR) that is gener- ated when relativistic electrons propagate through an oriented crystal target has been studied both theoreti- cally and experimentally in sufficient detail (see, e.g., monograph [1] and review [2]). The most characteristic feature of PXR in the relativistic case is the quasi- monochromatic emission (with the possibility of fre- quency tuning) at both small and large angles relative to the direction of the incident particle beam. In contrast, the coherent and noncoherent bremsstrahlung is pre- dominantly concentrated along the incident beam direction, although both types can also, in principle, exhibit partial diffraction on the crystal planes. In the case of nonrelativistic electrons, the angular distribu- tions of emission according to all mechanisms become virtually isotropic, which makes possible interference between the PXR and the coherent bremsstrahlung (CB) [3]. In what follows, the total coherent (CB plus parametric X-ray) radiation generated by nonrelativis- tic electrons in a crystal will be referred to as CB&PXR. In the total radiation spectrum, even the intense CB&PXR peaks are masked by the bremsstrahlung background and can be revealed only using a detector possessing high spectral and angular resolution. The investigations of CB&PXR are stimulated by the fact that, according to recent estimates [4], the spec- tral density of this radiation in a narrow frequency interval ∆ω/ω ~ 10 –3 is comparable with the spectral density of synchrotron radiation. Therefore, it is possi- ble to create a quite compact tunable source of mono- chromatic X-ray radiation for crystallographic investi- gations and structural analysis. At present, several experimental investigations of the radiation generated by nonrelativistic electrons in crystal targets have been reported [5–7], but no quanti- tative interpretations of the peak intensities have been proposed until now, because the observed radiation was considered only in terms of the mechanism of CB emis- sion. The CB&PXR model proposed in [3] makes pos- sible adequate interpretation of such radiation spectra and our experiments are aimed at further verification of this theory. Below, we report the results of experimental investigations of the properties of X-ray radiation and their interpretation in terms of the theory [3] for elec- trons with energies in the 50–100 keV range. Let us first briefly consider the main requirements on the experimental setup and conditions. Charged par- ticles in a beam propagating in a crystal target exhibit elastic and inelastic collisions, which lead to an increase in the angular and energy dispersion of the beam. The influence of electron scattering in a crystal on the CB&PXR characteristics becomes significant when either the full width at half maximum (FWHM) (∆v/v) of the velocity distribution or the FWHM (∆θ) of the angular distribution of particles in the beam is Coherent Bremsstrahlung and Parametric X-ray Radiation from Nonrelativistic Electrons in a Crystal V. G. Baryshevsky, K. G. Batrakov, I. D. Feranchuk, A. O. Grubich, A. A. Gurinovich*, A. S. Lobko, A. A. Rouba, P. F. Safronov, V. I. Stolyarsky, B. A. Tarnopolsky, and A. P. Ulyanenkov Institute for Nuclear Problems, Belarus State University, Minsk, Belarus * e-mail: gur@inp.minsk.by Received December 29, 2005 Abstract—X-ray radiation generated by nonrelativistic electrons interacting with a crystal target exhibits sev- eral distinctive features in comparison to the relativistic case. The difference is related to the interference of the parametric X-ray radiation and coherent bremsstrahlung, which takes place for the nonrelativistic electrons. The characteristics of this radiation have been studied in the Bragg and Laue geometries in an electron micro- scope using a beam of electrons with energies in the 50–100 keV range. The necessary requirements on the tar- get parameters, the measuring instrumentation, and the experimental geometry are established. Variation of the X-ray radiation frequency depending on the angle of electron beam incidence on the target in the region of non- relativistic electron energies has been observed for the first time. The X-ray radiation frequency has been also studied as a function of the primary electron beam energy. Tunable soft X-ray radiation with quantum energy in the range below 1 keV is obtained. The radiation quantum yield per electron within a unit solid angle amounts to ~10 –8 . PACS numbers: 61.85.+p, 13.88.+e DOI: 10.1134/S1063785006050087