Chia-Jung “Charlie” Liu

Part 1: A new method for optical measurement of proton polarization. A new method has been developed to measure the polarization of low energy (10 keV to 100 keV) protons. The basic principle of this method is based on a quantum beat measurement within the context of beam-foil spectroscopy. Following the beam-foil neutralization and excitation, the emitted 2P $\to$ 1S Ly-$\alpha$ photon is circularly polarized to a degree depending on the initial proton polarization and time of flight downstream from the exciter foil because of the hyperfine interaction between the proton and electron. The beam-foil technique was used for the first time to measure the proton polarization at BNL for its 20 keV polarized $H\sp{-}$ beam. The degree of circular polarization was analyzed by an optical polarimeter consisting of a $MgF\sb2$ retardation waveplate, a 4-mirror linear polarizer and a solar blind photomultiplier. Cascading into the 2P state from the higher excited states like 3D and 3S was taken into account in the data analysis. The result of the polarization measurement agrees with the measurement by the other two polarimeters in the beam line. The analyzing power of this polarimeter is 18.5 $\pm$ 0.05% at the optimum position. The given uncertainty is due principally to the uncertainty in the initial population production ratio of higher excited states to the 2P state. The overall detection efficiency of the beam-foil proton polarimeter is $\sim$4 $\times$ 10$\sp{-10}$. This polarimeter is equally useful as a polarization tuning and measuring device for both polarized $H\sp{+}$ and $H\sp{-}$ beams.

Part 2: Orientation of H(2P) by beam-tilted-foil interaction. The circular polarization of Ly-$\alpha$ photons resulting from beam-tilted-foil interaction was measured between 9 keV and 20 keV with foil tilt angles up to 60$\sp\circ$. The work represents the first data of beam-tilted-foil experiment on proton, the simplest projectile in heavy ion beam foil interaction. The data is important in regards of the importance of the surface effect in beam-foil interaction process. Various models used to fit the data are discussed.