Elastic photon scattering cross sections on O-16 have been measured in the energy range 27-108 MeV. These data are inconsistent with a conventional interpretation in which the electric and magnetic polarizabilities of the bound nucleon are unchanged from the free values and the meson-exchange seagull amplitude is taken in the zero-energy limit. Agreement with the data can be achieved by invoking either strongly modified polarizabilities or a substantial energy dependence to the meson-exchange seagull amplitude. It is argued that these seemingly different explanations are experimentally indistinguishable and probably physically equivalent.

Angular distributions for photon scattering from C-12 and He-4 have been measured using continuous wave bremsstrahlung from the Saskatchewan Accelerator Laboratory pulse stretcher ring. Data for carbon were taken at 158.8, 195.2, 197.2, 247.2, and 290.2 MeV end-point energies, and for helium were taken at an end-point energy of 158.8 MeV. A large NaI(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 detector allowed a separation of elastic from inelastic photon scattering for the first time at these energies. The angular distributions for elastic scattering are in only fair agreement with delta-hole theory and theory based on the optical theorem at forward angles, and completely disagree with theory at backward angles. Measured cross sections for inelastic scattering leading to the 4.43 MeV state in carbon are small compared to the elastic scattering at forward angles, but are dominant at backward angles. This experiment is the first to separate elastic from inelastic photon scattering at these energies.

Impact parameter selected excited state populations were measured for [sup 36]Ar+[sup 197]Au reactions at [ital E]/[ital A]=35 MeV in order to better understand population inversions observed in a previous measurement of [sup 14]N+Ag reactions at [ital E]/[ital A]=35 MeV. The present impact parameter selected measurements revealed such population inversions to be most prominent in low multiplicity peripheral reactions. The excited state population for central collisions approach statistical model predictions for [ital T][approx]4 MeV.

The proton Compton effect has been studied in the region between the threshold for pion photoproduction and the \ensuremath{\Delta}(1232). The measurements were performed using bremmstrahlung from the high duty-factor electron beam available at the Saskatchewan Accelerator Laboratory. Elastically scattered photons were detected with an energy resolution of approximately 1.5% using a large NaI total absorption scintillation detector. Differential cross sections were measured for photon energies in the range 136 MeV\ensuremath{\le}${\mathit{E}}_{\ensuremath{\gamma}}$\ensuremath{\le}289 MeV and for angles in the range 25\ifmmode^\circ\else\textdegree\fi{}${\mathrm{\ensuremath{\theta}}}_{\mathrm{lab}}$135\ifmmode^\circ\else\textdegree\fi{}. The angular distributions and the excitation functions derived from these data are in agreement with recent theoretical analyses. The results were interpreted within a formalism based in part on dispersion relations to obtain model-dependent estimates of the electric and magnetic polarizabilities, \ensuremath{\alpha}\ifmmode\bar\else\textasciimacron\fi{} and \ensuremath{\beta}\ifmmode\bar\else\textasciimacron\fi{}. We find, subject to the dispersion sum rule constraint \ensuremath{\alpha}\ifmmode\bar\else\textasciimacron\fi{}+\ensuremath{\beta}\ifmmode\bar\else\textasciimacron\fi{}=(14.2\ifmmode\pm\else\textpm\fi{}0.5)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$ ${\mathrm{fm}}^{3}$, that \ensuremath{\alpha}\ifmmode\bar\else\textasciimacron\fi{}=(9.8\ifmmode\pm\else\textpm\fi{}0.4\ifmmode\pm\else\textpm\fi{}1.1)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$ ${\mathrm{fm}}^{3}$ and \ensuremath{\beta}\ifmmode\bar\else\textasciimacron\fi{}=(4.4\ensuremath{\mp}0.4\ensuremath{\mp}1.1)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$ ${\mathrm{fm}}^{3}$, which are consistent with the best previous measurements.

We have measured the Compton-scattering cross section on hydrogen at 60-degrees and 135-degrees using monochromatic tagged photons spanning the energy between 32 and 72 MeV. These data, when analyzed with a low-energy expansion of the scattering cross-section formula, provide a determination of values for the electric and magnetic polarizabilities of the proton. We find, respectively, alphaBAR = (10.9 +/- 2.2 +/- 1.3) x 10(-4) fm3 and betaBAR = (3.3 -/+ 2.2 -/+ 1.3) x 10(-4) fm3, assuming the model-independent constraint alphaBAR + betaBAR = 14.2 x 10(-4) fm3.