Polarimetry of Short Pulse Gamma-rays and Positions

We have made a basic study of a polarized positron source for the next generation linear collider, JLC[1][2]. This is based on a new idea that polarized positrons are pair-created from polarized γ -rays produced through Compton scattering of circularly polarized laser lights o relativistic electron beams[3][4]. Since a pulse duration of γ -rays thus produced is extremely short i.e. 20 psec, the polarization of γ -rays cannot be determined by an ordinary method in which one measures an individual scattering process of a γ ray on an electron in a magnetized iron. Using the simulation code GEANT that the intensity of γ -rays penetrating through a magnetized iron depends on the relative spin direction of γ -rays and electrons. We will rep ort a design of a polarimeter both for polarized γ -rays and positrons based on simulation studies.