Математика, 2005, ¹2 ON THE PARAMETRIC X-RAYS ALONG THE VELOCITY OF AN EMITTING PARTICLE V. Likhachev1 1 , N. Nasonov1 , A. Tulinov2 , P. Zhukova1 Laboratory of Radiation Physics, Belgorod State University, Belgorod, Russia 2 Moscow State University, Moscow, Russia The forward PXR from relativistic electrons crossing a thick crystalline target (the thickness of the target exceeds an absorption length) is studied theoretically with account of the contributions of PXR, transition radiation and bremsstrahlung to the formation of a total emission yield. <...> The peculiarities in an emission spectrum observed in the recent Tomsk experiment are explained on the basis of the developed theory. 1. <...> INTRODUCTION When a fast charged particle crosses a crystalline target it can emit X-rays due to the coherent Bragg scattering of its Coulomb field by system of parallel atomic planes of the crystal. <...> This emission mechanism well known as the parametric X-rays (PXR) has been studied theoretically and experimentally in detail [16], but this statement is true for the emission flux propagating to the Bragg scattering direction only. <...> An additional PXR flux propagating along an emitting particle velocity has been observed last time only [7, 8]. <...> Two different experimental procedures have been used in experiments [7, 8] in order to separate a low-power PXR signal on the background of broadband bremsstrahlung and transition radiation. <...> A thin light crystal has been used in [7] to suppress an influence of photoabsorption and multiple scattering (and bremsstrahlung consequently). <...> The main contribution to background in the experiment [7] was formed by transition radiation. <...> Mentioned advantages of the discussed approach was attended by one substantial disadvantage consisting in the occurrence of an additional X-ray flux due to dynamical diffraction effect in the transition radiation emitted from a crystal [9]. © Likhachev V., Nasonov N., Tulinov A., Zhukova P., 2005. 98 An alternative experimental procedure was used in the experiment [8]. <...> In addition to this there were no dynamical effects in the transition radiation contribution since a photoabsorption length was less then the thickness of the target. <...> It has been shown in the experiment that the structure of total emission spectrum in the vicinity of Bragg frequency where PXR yield was concentrated depends strongly on the value of orientation angle between the velocity <...>