Studies of fundamental photon scattering processes using n-capture gamma-rays

Intense monochromatic photon beams (∼10⁶ γ/cm² · s on the target) in the 0.5-11.4 MeV range generated by the (n, γ) reaction on V, Cr, and Ni were used for a systematic study of the various elastic and inelastic photon scattering processes. To avoid complications caused by the coherency of the scattering processes, the experimental conditions (such as E, Z, and the scattering angle θ) were selected in such a way that maximum isolation of the contribution of each process was obtained. Thus, the contribution of nuclear Thomson (NT), nuclear resonance (NR), Rayleigh (R), and Delbrück (D) scattering processes were studied in separate experiments. Generally a fair agreement was obtained with theory. The effect of vacuum polarization in D scattering at E = 6.8-11.4 MeV, θ ∼ 1°, and high Z was found to be huge and constitutes a definitive evidence for the contribution of the real D amplitudes. Interference effects between NT and NR amplitudes, between D and R amplitudes, and between NR and D amplitudes were obtained. Strong evidence for the contribution of Coulomb corrections to D scattering from a U target is given. In addition, the results of incoherent elastic and nuclear Raman photon scattering from various deformed and spherical heavy nuclei are presented.