For a number of years now, siloxanes have been the materials of choice for coating vessels used in the production and short-term storage of hyperpolarized xenon. The methods used to apply this material, however, often vary from one research group to another and it is commonly reported that it is difficult to obtain cells with consistently long spin-lattice relaxation times (T1) and high-polarization levels. In a series of controlled experiments individual production variables were altered and optimized, leading to improved protocols for the reliable production of high-quality siloxane-coated cells. During these studies we discovered that the surface-induced relaxation rates in bare and coated Pyrex cells differ profoundly. This information on Xe relaxation helps to define the limits on the way pumping cells can be improved and suggests the need for further fundamental work on relaxation mechanisms.

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