where E is the energy of an x-ray quantum, eV. For example, for the energy of the characteristic radiation of the K series of
copper, θcr ≈ 4 mrad. Thus, the angle of capture by an individual capillary equal, obviously, to two critical angles, is very
small. At the exit from the capillary system, we also obtain low divergence of the beam of x-radiation, the value of which
within the framework of a geometrico-optical treatment is equal to the critical angle. In contrast, in the individual cases
described by the wave theory the divergence of the beam of x-radiation may be even less than the critical angle .