An apparatus for preparing isotopically pure 4He

摘要

A cryostat has been constructed for extracting pure He4 from He II of natural isotopic composition by means of a heat flush technique. It is shown that the method is in principle capable of yielding He4 which is entirely devoid of He3 isotopic impurities. A secondary heat flush, operated in conjunction with a conical heat exchanger of novel design, was used to place an experimental lower bound of 2 × 1015 on the ratio of the product, a standard sufficient for all present or projected applications requiring isotopically pure He4. The apparatus produces 2 000 1 (at standard temperature and pressure) of He4 per thermal cycle. The design of future purifiers is discussed.