Total Photoabsorption off the Proton and Deuteron at Intermediate Energies

Total photoabsorption cross section experiments at GRAAL are described. Measurements have been done in the energy range E_γ = 600-1500 MeV, with liquid hydrogen and deuterium targets, using the laser back scattered gamma beam and the large aperture LAGRANγE detector. Electromagnetic and hadron backgrounds have been analyzed. A subtraction method, using the empty target measurements, has been applied to derive directly σ_tot for the free proton and deuteron. Experimental results for σ_tot are compared to existing literature data. Large difference between the proton and deuteron, normalized by factor 2, in photoabsorption cross section is seen particularly in the D15 nucleon resonance region.