Stainless-steel cells with a small cooled length (window to hot zone) to tube diameter ratio designed for use at electron storage rings have been constructed and tested using barium metal. Under optimum conditions of barium sample size and helium buffer gas pressure the cell and oven system can be operated for at least 8 h with constant (within experimental errors) line-of-sight number densities, Nl, of ∼1016 cm -2. When Nl values begin to fall toward the end of their initially constant period or the light path becomes blocked by barium condensed at the edge of the hot zone, the original cell conditions can be regenerated within 15 min. These regeneration procedures provide essentially unlimited (though segmented) operation of the system with constant Nl values.
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