New measurements of coherent and incoherent photon scattering by low, medium and high Z atoms

Coherent and incoherent photon scattering by bound electrons in low, medium and high Z atoms, over energies of 0.145-1.33 MeV and scattering angles below 150 (momentum-transfer range 0-0.4 mc) and from 150 to 1500 (0.1-4.0 mc), have been investigated experimentally. The results of the present relatively high precision measurements have also been compared with the predictions of new theoretical calculations for bound-electron incoherent and coherent scattering in the incoherent scattering-factor and form-factor approximations and for the Rayleigh and Delbrueck scattering amplitudes over a high momentum-transfer range, to give a critical verification of the theory. It was found that for 0.145 MeV photons scattered with low momentum transfer, the F(q, Z) formalism is valid for low and medium Z atoms but not for the high Z (Z = 82) atom. At all energies and in the low momentum-transfer range studied in the present work, the S (q, Z) formalism was found to be adequate for bound-electron incoherent scattering for all the atoms. The effect of Delbrueck scattering of 1.115 MeV photons was found to be quite obscured up to the largest angle (1350) reported in this paper. (author)