Tuesday, September 25, 2012
10:00am (110 INSCC)
Title: The fundamental physics of spin-exchange optical pumping (SEOP) and a few applications of the resultant hyperpolarized 129Xe
This thesis is focused on the fundamental physics of spin-exchange optical pumping (SEOP) and a few applications of the resultant hyperpolarized 129Xe.
During SEOP, noble-gas and Rb atoms repeatedly collide. During these collisions the Rb valence-electron wavefunction overlaps with the noble-gas nucleus and if either the noble-gas nucleus or Rb electron are highly spin-polarized then the other will experience, on average, a small additional magnetic field that will manifest itself as a shift in the Larmor frequency. The size of the frequency shift is proportional to the magnetization of the polarized atoms and consequently can be used to perform polarimetry. Pulsed NMR was used to measure 3He and 129Xe Larmor frequency shifts, and optically detected continuous-wave electron paramagnetic resonance (EPR) was used to monitor the 87Rb hyperfine transition frequencies.
A successful calibration of the size of the frequency shift due to 129Xe-Rb collisions was done and, using this calibration, initial 129Xe polarimetry data was acquired by monitoring the 87Rb EPR frequency as a function of Xe concentration. The 129Xe polarimetry results were inconclusive due to an unexplained result regarding the sign of the frequency shift, however extensive progress was made in understanding the systematics associated with this type of measurement.
Hyperpolarized 129Xe from the Utah flow-through polarizer was also used in a biological application. The Larmor frequency of dissolved hyperpolarized 129Xe was used to detect and characterize the binding of Xe to wild-type and several mutations of bovine pancreatic trypsin inhibitor (BPTI) protein. In addition to hyperpolarized 129Xe NMR, 1H and 15N heteronuclear single quantum coherence (HSQC) NMR was done on Y23A BPTI in the presence of dissolved Xe. The results confirmed the existence of Xe binding to the cavity in Y23A and were consistent with the hypothesis that smaller cavities lead to bigger 129Xe chemical shifts.
Full program available here (PDF).