ANGULAR AND POLARIZATION DEPENDENCE OF COMPTON-SCATTERING FROM HE-4 IN THE TRIANGLE-RESONANCE REGION

Using linearly polarized tagged photons from coherent bremsstrahlung, differential cross sections and beam asymmetries for Compton scatterin g by He-4 have been measured at MAMI in the energy interval between 15 0 MeV and 500 MeV for scattering angles of theta(gamma)(lab) = 37 degr ees, 93 degrees and 137 degrees, thus largely increasing the available data base. Improved calculations in terms of the Delta-hole model com pletely fail to describe the data at large scattering angles. The same proved to be true for a schematic model, even after taking into accou nt properties of nuclear photo-absorption in very detail. (C) 1998 Els evier Science B.V. All rights reserved.