PHOTON SCATTERING FROM C-12 AND HE-4 NUCLEI NEAR THE DELTA(1232) RESONANCE

Angular distributions for photon scattering from C-12 and He-4 have be en measured using continuous wave bremsstrahlung from the Saskatchewan Accelerator Laboratory pulse stretcher ring. Data for carbon were tak en at 158.8, 195.2, 197.2, 247.2, and 290.2 MeV end-point energies, an d for helium were taken at an end-point energy of 158.8 MeV. A large N aI(Tl) gamma ray spectrometer with 1.7% resolution was used to detect the scattered photons at laboratory scattering angles, ranging from 20 degrees to 150 degrees. The excellent energy resolution of the NaI de tector allowed a separation of elastic from inelastic photon scatterin g for the first time at these energies. The angular distributions for elastic scattering are in only fair agreement with delta-hole theory a nd theory based on the optical theorem at forward angles, and complete ly disagree with theory at backward angles. Measured cross sections fo r inelastic scattering leading to the 4.43 MeV state in carbon are sma ll compared to the elastic scattering at forward angles, but are domin ant at backward angles. This experiment is the first to separate elast ic from inelastic photon scattering at these energies.