A Rapid and Precise Probe for Measurement of Liquid Xenon Polarization

摘要

The relaxation time of liquid ~(129)Xe is very long (>15 min) and the signal at thermal equilibrium is weak. Therefore, determination of the absolute polarization enhancement of hyperpolarized ~(129)Xe by direct measurement is tedious. We demonstrate a fast and precise alternative, based on the dipolar field created by liquid hyperpolarized ~(129)Xe contained in a cylindrical sample tube. The dipolar field is homogeneous in the bulk of the tube and adds to the external field, causing a shift in the Larmor frequencies of all nuclear spins. We show that the frequency shift of the proton in CHCl_3 (chloroform), which dissolves homogeneously in xenon over a fairly broad temperature range, is an excellent probe for ~(129)Xe polarization. Frequency measurements are precise and the experiment is much faster than by direct measurement. Furthermore the ~(129)Xe polarization is minimally disturbed since no rf pulses are applied directly to ~(129)Xe and since chloroform is a fairly weak source of ~(129)Xe relaxation. The experiments are reproducible and require only standard NMR instrumentation.