These are the most stable pump for noble gas loads. Noble diodes were developed to pump noble gases. In every instance but one they are identical to a standard diode. The difference is the use of one tantalum cathode in place of one of the two titanium cathodes in the standard pump. The tantalum, because of its larger atomic number, produces a greater number of energetic neutrals which can bury themselves in locations which are less subject to resputtering.
Tantalum is somewhat less effective than titanium as a getter.
Another fact of note is the lessened solubility of hydrogen in tantalum at elevated temperatures. Since elevated temperatures will be encountered during prolonged starting, it would be wise to avoid applications which require this pump to handle large amounts of hydrogen. Naturally, applications differ. We have a wide variety of prior applications to draw upon. Hydrogen Diode Pumps are also similar to standard diodes.