<p>The first measurements of the two- and three-body photodisintegration of longitudinally</p><p>polarized 3He with a circularly-polarized gamma-ray beam were carried out at the High Intensity gamma-ray Source facility located at Triangle Universities Nuclear Laboratory (TUNL). A high pressure 3He target, polarized via spin exchange optical pumping with alkali metals, was used in the experiments. The protons from the two-body photodisintegration experiment were detected using seventy two silicon surface barrier detectors of various thicknesses while the neutrons from the three-body photodisintegration were detected with sixteen 12.7 cm diameter liquid scintillator detectors. The spin-dependent cross sections and the contributions from the two- and three-body photodisintegration to the 3He Gerasimov-Drell-Hearn sum rule integrand were extracted and compared with state-of-the-art three-body calculations at the incident photon energies of 29.0 MeV (two-body) and 12.8, 14.7, and 16.5 MeV (three-body).</p><p>These are the first measurements of the contributions of the two- and three-body photodisintegration of 3He to the GDH integrand. These measurements were found to be in good agreement with the theoretical calculations which include the Coulomb interaction between protons in the final state. They also reveal-for the first time-the importance of the three-nucleon forces and the relativistic single-nucleon charge corrections which are responsible in the calculations for the observed difference</p><p>between the spin-dependent cross sections.</p> / Dissertation