Certain scientific applications require helium of greater purity than that routinely available. This paper describes a laboratory- size apparatus which reduces impurities in helium to less than 1 part per billion. The unit employs easily available, low-cost liquid nitrogen as a refrigerant to cool activated charcoal for the cyclic adsorption of impurities. The essential differences between the new purifier and previous adsorption units are the use of highly purified helium to purge and repressure the charcoal during and after regeneration and regeneration of the adsorbent before neon emerges. The unit produces a few hundred cubic centimeters of highly purified helium per minute, the amount depending upon the helium pressure required and the chosen cycle time. Continuous safe operation is achieved with only periodic observation and requires about 20 liters of liquid nitrogen per day.
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