A polarized photon beam produced by coherent pair production in oriented graphite

Abstract Attenuation by coherent pair production in higly oriented, compression annealed, pyrolytic graphite has been used to polarize a 16-GeV bremsstrahlung beam. The polarizer consists of 61 cm of graphite crystals, whose reciprocal lattice vectors are oriented at 10.5 mrad to the normal to the beam direction, and can be rotated by 90° about the beam line to rotate the plane of polarization. A functionally identical assembly of length 30.5 cm was used as an analyzer to measure the polarization of the beam with the SLAC pair spectrometer. The beam produced intensities greater than 4 × 10 8 equivalent quanta per beam pulse and had a measured polarization of 0.255±0.020.