A new mechanism of absorption anisotropy of high energy photons in a crystal

A new orientation effect accompanying the passage of high energy photons through a crystal is described. The origin of this effect is connected with the inhomogeneity of the photon flux caused by the absorption of photons in the regions of intensive pair production near atomic nuclei. This leads to a decrease of the pair production rate when photons are aligned within microradian angles of a crystallographic axis. Diffraction of γ-quanta hampers a manifestation of this effect, making it pronounced only in the energy region where the process of synchrotron-like pair production arises. We have developed a technique, which allows us to determine the minimum photon energies needed to observe the effect under consideration. The absorption anisotropy of γ-quanta must noticeably influence their absorption when photon incident angles with respect to crystallographic axes are smaller than 10 μrad. It is possible to observed this effect at present.