ABSTRACT:The effect of reduced pressure on the polarization of 129 Xe has been examined in batch and continuous flow modes aiming at developing a simple and convenient hyperpolarizing system. The effect of foreign gases was found to show a different tendency at reduced pressure as low as 0.15 atm compared to that near atmospheric pressure. For example, 129 Xe polarization in binary mixtures of Xe and N 2 was larger than that observed in ternary mixtures of Xe, N 2 , and 4 He when compared with the same Xe content, and the highest polarization of 63.6% was given by the 5% Xe þ 95% N 2 mixture in the batch mode. The most noticeable result in the flow mode was that 129 Xe polarization reached a plateau at 0.15 atm when cell pressure was reduced from atmospheric pressure, being enhanced to about twice of that observed near atmospheric pressure. Also demonstrated is the use of isotopically enriched 129 Xe gas at reduced partial pressure. This will be devoid of the anesthetic side effects of Xe while making use of enhanced polarization at reduced pressure, leading to the development of a simple and convenient hyperpolarizing system for medical use.

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Nano-materials, such as zeolites with nano-sized pores, are attractive new materials in industry, and are expected to offer a promising future efficient way to settle problems in environmental ecology as well. 1 It is important when developing such new materials for different purposes to evaluate physicochemical properties, such as the surface area, cage/pore structure, adsorption coefficient and surface distribution of metal ions. Surface area, for example, has usually been determined by a classical volumetric or gravimetric method, such as B.E.T. adsorption analysis using nitrogen as an adsorbent gas, and advanced techniques, such as an electronic microscope, SEM or TEM also, solid state NMR have recently been used to analyze the physicochemical properties of a surface in detail.129 Xe NMR has long been applied to analyze a porous structure in zeolites, 2 and quite recently the most interesting topic, hyperpolarized 129 Xe NMR, have emerged, in which the sensitivity can be enhanced by several orders by utilizing the optical pumping technique.3 It is highly expected that such a sensitivity enhanced 129 Xe NMR will be widely used to characterize nano-materials that have been newly synthesized, or of wide applicability in industry and medicine. In these 129 Xe NMR studies, basic parameters, such as the surface area and the adsorption energy are also hoped to be determined by using Xe as an adsorbent. 129 Xe NMR can be used for this purpose without any facilities of the traditional methodology, since it can provide a measure of the amount of adsorbed Xe through the intensity of the 129 Xe adsorbed signal. Therefore, in order to examine the applicability of 129 Xe NMR in obtaining basic adsorption parameters of the surface area and the adsorption energy for nano-materials, the temperature and pressure dependences are investigated for the chemical shift as well as the signal intensity, i.e., peak area, in the 129 Xe NMR of the present study. Experimental Reagents and chemicalsThe sample used was ZSM-5 (JRC-Z5-70Na from Mobil Catalysts Corp., Japan, Si/Al ratio = 92.5), supplied as a standard sample from Japan Catalysis Association. ZSM-5 is one of the micro-porous zeolites with an MFI structure, which is expected to contribute to improving the environment as an exchange agent for the separation of alcohol, NO removal etc. There is no super cage existing in ZSM-5, although X-or Ytype zeolite has them as the FAU structure. The pore size is 0.56 × 0.53 nm in linear structure and 0.55 × 0.51 nm in zigzag pore structure. Two structures are crossed with each other and form a 3D structure. Standard Xe gas that contains a natural abundance of 26.24%129 Xe was purchased from Japan Air Gases Ltd., and used after drying by passing over K-Na alloy, or passing through Minifine Purer supplied from Liquid Gas Co. Apparatus and procedureThe zeolite sample and Xe gas were treated in a fully shielded system made by glass-blowing. The sample was weighed into a Temperature and pressure dependences of the 129 Xe NMR chemical shift ...