  The Na59 collaboration aims to measure the linear polarization of its photon
beam in the 20-170 GeV range, using an aligned thin crystal. The tracks of
$e^-/e^+$ pairs created in two different crystal targets, germanium and
diamond, are reconstructed to obtain the photon spectrum. Using the
polarization dependence of the pair production cross section in an aligned
crystal, photon polarization is obtained to be 55% at the vicinity of 70 GeV.
