CIRCULAR POLARIZATION OF HIGH-ENERGY $gamma$ RAYS BY BIREFRINGENCE IN CRYSTALS

It was shown in a previous work that thick single crystals can be used as polarizers and polarimeters for highenergy gamma rays because of coherence effects in pair production. As a consequence of the effects previously discussed, it is shown here that single crystals are also birefringent. This makes it possible to use a crystal of appropriate thickness as the high-energy analog of a quarter-wave lengih plate to convert linear into circular polarization, and vice versa. In this way it will be possible to produce and analyze circularly polarized gamma beams of very high energy. (H.D.R.)