Absolute linear polarization gauge for low-energy photons

The Σ-asymmetry of the reaction γ→+ ¹²C→ ⁸Be+ ⁴He→3α , through ⁸Be in the ground state is shown to be unity. We present an experimental setup, based on an arrangement of silicon detectors associated with a photon tagging system, which is able to extract the ⁸Be ground state events from the total reaction yield. The use of such a setup as an absolute gauge for the degree of linear polarization of a photon beam was studied by Monte Carlo simulation.