A gridded ionization chamber with a movable cathode for precise measurements of W-values in highly purified rare gases

A single gridded ionization chamber with a movable cathode was constructed in order to measure W -values in highly purified rare gases without ambiguity. The chamber gases were continuously purified with a purifier filled with many pellets of titanium-barium getter. The purifier proved to be so powerful as to reduce impurities in rare gases to the level of 1 ppb or less. Performance tests of the chamber were made by measurements of W -values of argon-methane mixtures relative to that of argon. The measurements were made with a precision of ±0.14%.