Alkali-Metal Spin-Destruction Rates in Rb-Xe and Cs-Xe Systems

We measure and compare the spin-destruction rates for Rb and Cs in a He(94%)-N₂(3%)-Xe(3%) gas mixture. The measurements are crucial to understanding which alkali-metal is the most efficient for polarizing ¹²⁹Xe and are carried out in two matched sets (one each for Rb and Cs) of four sealed vapor cells, allowing us to determine the respective spin-destruction rates as a function of total gas density at fixed composition. Optically detected pulsed EPR is used to observe the slowest polarization-decay component of the alkali-metal atoms in the dark. We measure a Xe-Cs rate about 20% slower than that of Xe-Rb over the density range of one to a few amagats. Spin destruction in this range is dominated by binary collisions with Xe and very-short -lifetime Rb-Xe or Cs-Xe van der Waals molecules. Our Rb data are consistent with Nelson and Walker’s results and corresponding theoretical model [1], which we have also adapted to interpret our Xe-Cs data. Considering the reported 10% faster spin-exchange rate coefficient for Cs-Xe [2], we estimate a ≈40% improvement in Cs SEOP efficiency vs. Rb. We are currently attempting to verify this estimate with our own spin-exchange rate-coefficient measurements for these same cells.