x / 99 04 02 9 v 1 2 8 A pr 1 99 9 Birefringence of high - energy γ - quanta in the single crystals

Problems of the experimental observation of the birefringence of high energy γ-quanta propagating in single crystals are discussed. 1 Introduction The birefringence of γ-quanta with energies > 1 GeV propagating in single crystals was predicted in [1]. The main process by which γ-quanta are absorbed in single crystals is the electron-positron pair production. The cross section of the process depends on the direction of linear polarization of the γ-quanta relative to the crystallographic planes. As a result of interaction with the electric field of the single crystal, a monochromatic, linearly polarized beam of γ-quanta comprises two electromagnetic waves with different refractive indices, so that linear polarization is transformed into circular polarization or vice versa. This polarization phenomenon would be observed for symmetric orientations of single crystals with respect to the direction of motion of γ-quanta. The general case of the propagation of γ-quanta in single crystals was considered in [2, 3, 4]. In these papers it was shown that the propagating γ-beam is a superposition of the two elliptically polarized waves and unpolarized γ-beam obtain some degree of circular and linear polarization after passage through a single crystal. In case, describing in [1], the beam of γ-quanta is a superposition of the two linearly polarized waves and unpolarized beam obtain only some degree of linear polarization after propagation in single crystals. It is important to note that no experiments have been performed to date to corroborate the transformation of γ-beam polarization in single crystals, despite the notable lapse of time since the publication of [1]. It is at least two essential purposes for experimental investigations of the birefringence in single crystals. There are: 1)The nature of phenomenon is a manifestation of the nonlinearity of Maxwell's equations for the electromagnetic vacuum. Of course, a single crystal contain carriers of electric charge (electron, ions, etc), but their direct presence is significant only if the frequencies of the electromagnetic radiation passing through the single crystal are low, while at high frequencies the fields formed by these charges play the main role. Thus the observation of the birefringence in single crystals is indirect experimental proof of existence of the similar effect in electromagnetic vacuum (see [5] and the literature cited therein); 2) Some possibilities exist to utilize this phenomenon in experiments on modern accelerators (see [4, 6, 7] and the literature cited therein).