Analysis of the effect of foreign gases in the production of hyperpolarized 129Xe gas on a simple system working under atmospheric pressure

Experimental conditions that affect the degree of polarization of Xe-129 gas were tested for a higher degree of polarization to facilitate a laboratory use of Xe-129 NMR, primarily on the effect of addition of foreign gases. When He, N-2, or D-2 gas was added separately to pure Xe gas with natural isotope abundance, D-2 gas gave better results than the others in enhancing the degree of polarization in Xe-129 atom. When these gases were added in mixture, however, N-2 plus He was proved to be more efficient than D-2 or He in enhancing the degree of polarization. As a result, the degree of polarization was found to be increased by more than an order, when diluent gases were properly mixed; polarization as high as 35% was reached at gas composition of 5% Xe, 10% N-2, and 85% He, whereas only a few percent was attainable when Xe gas was polarized without mixing any foreign gases [J. Magn. Reson. 150 (2), 156-160 (2001)]. These results were discussed on a basis of quenching and buffer effects of foreign gases. Polarization was also measured after separating the pure Xe gas from the mixture; value of 22% was obtained for the Xe gas isolated after solidification in liquid nitrogen trap. Build-up time of the polarization was also tested, which did not change remarkably depending on the gas composition. (C) 2002 Elsevier Science (USA). All rights reserved.