First Study of Three-body Photodisintegration of 3He with Double Polarizations at HIGS

Abstract

This dissertation describes the first study of three-body photodisintegration of polarized 3He (γ3He → npp) with a circularly polarized photon beam. This measurement was carried out at the High Intensity γ-Ray Source(HIγS) facility located at Duke University Free Electron Laser Laboratory and the incoming photon energy was 11.4 MeV. A high-pressure polarized 3He target based on spin exchange optical pumping (SEOP) of hybrid alkali was employed. Two methods--Nuclear Magnetic Resonance (NMR) and Electron Paramagnetic Resonance (EPR)--were used to measure the polarization, which was determined to be ∼ 42%. The data from the experiment were analyzed and a GEANT4 simulation was carried out to determine the corrections for finite geometry, neutron multiple scattering and detector efficiencies used in this experiment. The results are compared to the state-of-the-art three-body calculations and agreements are observed within rather large statistical uncertainties of the measurement. This experiment represents the first measurement of the asymmetry using spin-dependent 3He photodisintegration. The unpolarized differential cross section and helicity-dependent differential cross-section difference results are also presented and compared to the same theoretical calculations followed by a discussion of the results. Total cross section is also extracted using two different methods and agrees well with the theoretical prediction. New developments including a Sol-Gel coated pyrex 3He cell since the experiment are then presented. The in-beam test results of the aforementioned target cell from May 2009 test run are included and the prospect of future three-body photodisintegration is discussed in the end.