GDH at GRAAL with polarized H D target

Within the GRAAL collaboration, we have constructed a Polarized HD Target Factory, implanted at IPN Orsay. The expected properties of the HD targets and the results already obtained for the polarization of HD samples and the relaxation times are given. New possibilities to perform GDH experiments on polarized proton, neutron and deuteron are now opened, by using the high circular polarization of the GRAAL backscattered photon beams and the large effective longitudinal polarization of the HD target, resulting essentially from its good dilution factors. Polarized total cross sections concerning the isovector Drell-Hearn Gerasimov Sum Rule related to the proton neutron difference, could be measured with minimum systematic uncertainties: the target containing both polarized protons and neutrons. An experimental method, taking advantage of the 4pi GRAAL experimental set-up is described.