A NEW MECHANISM OF ABSORPTION ANISOTROPY OF HIGH-ENERGY PHOTONS IN A CRYSTAL

A new orientation effect accompanying the passage of high energy photo ns through a crystal is described. The origin of this effect is connec ted with the inhomogeneity of the photon flux caused by the absorption of photons in the regions of intensive pair production near atomic nu clei. This leads to a decrease of the pair production rate when photon s are aligned within microradian angles of a crystallographic axis. Di ffraction of gamma-quanta hampers a manifestation of this effect, maki ng it pronounced only in the energy region where the process of synchr otron-like pair production arises. We have developed a technique, whic h allows us to determine the minimum photon energies needed to observe the effect under consideration The absorption anisotropy of gamma-qua nta must noticeably influence their absorption when photon incident an gles with respect to crystallographic axes are smaller than 10 mu rad. It is possible to observe this effect at present.