Threshold photoneutron angular distribution and polarization studies of nuclei

The photoneutron method was applied to the study of (i) deuteron photodisintegration, (ii) giant magnetic dipole resonances in heavy nuclei, (iii) mechanism of radiative capture in light nuclei and (iv) isospin splitting of the giant dipole resonance in 60Ni. These studies were performed with the pulsed bremsstrahlung beam and high-resolution spectrometer available at the Argonne high-current electron linac. A threshold photoneutron polarization method was developed in order to search for the giant M1 resonance in hevy nuclei. A surprisingly small amount of M1 strength was found in 208Pb. Furthermore, the M1 strength for the 5.08-MeV excitation in 17O, the best example of a single-particle M1 resonance in nuclei, was found to be strongly quenched. In addition, the 17O(#betta#,n0)16O reaction was found to provide an ideal example of the Lane-Lynn theory of radiative capture. The interplay among the three components of the theory, internal, channel and potential capture, were evident from the data. An electron beam transport system was developed which allows the bremsstrahlung to impinge on the photoneutron target on an axis perpendicular to the usual reaction plane. This system provides an accurate method for the measurement of relative angular distributions in (#betta#,n) reactions. This system was applied to a high-accuracy measurement of the relative angular distribution for the D(#betta#,n)H reaction. The question of isospin-splitting of the giant dipole resonance in 60Ni was studied by using the unique pico-pulse from the accelerator and the newly installed 25-m, neutron flight paths. The results provide clear evidence for the effect of isospin splitting