The 129Xe nuclear spin polarization (P Xe) that can be achieved via spin-exchange optical pumping (SEOP) is typically limited at high in-cell xenon densities ([Xe] cell), due primarily to corresponding reductions in the alkali metal electron spin polarization (e.g. P Rb) caused by increased non-spin-conserving Rb-Xe collisions. While demonstrating the utility of volume holographic grating (VHG)-narrowed lasers for Rb/ 129Xe SEOP, we recently reported [P. Nikolaou et al., JMR 197 (2009) 249] an anomalous dependence of the observed P Xe on the in-cell xenon partial pressure (p Xe), wherein P Xe values were abnormally low at decreased p Xe, peaked at moderate p Xe (∼300 torr), and remained surprisingly elevated at relatively high p Xe values (>1000 torr). Using in situ low-field 129Xe NMR, it is shown that the above effects result from an unexpected, inverse relationship between the xenon partial pressure and the optimal cell temperature (T OPT) for Rb/ 129Xe SEOP. This interdependence appears to result directly from changes in the efficiency of one or more components of the Rb/ 129Xe SEOP process, and can be exploited to achieve improved P Xe with relatively high xenon densities measured at high field (including averaged P Xe values of ∼52%, ∼31%, ∼22%, and ∼11% at 50, 300, 500, and 2000 torr, respectively).
All Science Journal Classification (ASJC) codes
- Nuclear and High Energy Physics
- Condensed Matter Physics