A method and apparatus for the accumulation of hyperpolarized <;SUP>;129<;/SUP>;Xe is described. A gas mixture comprising <;SUP>;129<;/SUP>;Xe is flowed through a heat exchanger tube from the first end to the second end. Concurrently, the outer surface of the heat exchanger tube is controllably refrigerated, beginning with the second end, to a temperature low enough to freeze the <;SUP>;129<;/SUP>;Xe on the inner surface of the heat exchanger tube.