Fig. 1.

(A) SEOP-generated ¹²⁹Xe and ⁸³Kr spin polarization in mixtures containing 5% noble gas and 95% buffer gas as a function of total SEOP gas pressure. Using H₂ as buffer gas, the ¹²⁹Xe spin polarization (obtained at 378 K) is shown in red filled circles and the ⁸³Kr polarization (obtained at 440 K) is displayed as blue filled squares. For comparison, previous data from ref. 39 with N₂ as buffer gas is shown for ¹²⁹Xe SEOP at 378 K (green open circles) and for ⁸³Kr SEOP at 433 K (green open squares). In contrast, CH₄ is an inefficient buffer gas that led to low spin polarization (orange open triangles, taken from ref. 54). (B) The D₂ fluorescence at 780 nm (in arbitrary units, a.u.) measured at the front of the cell during SEOP indicates that sufficient radiation quenching with H₂ at 378 K (red circles) and at 433 K (blue squares) requires pressures above 50 kPa. Using N₂ (green open circles), the D₂ radiation is efficiently quenched at pressures above ∼5 kPa. Inset (i) shows the high D₂ fluorescence measured for Xe SOEP at 378 K with methane that is a very ineffective quenching gas.