Anomalous Residual Currents in the Ultrahigh Vacuum Use of Bayard-Alpert Ionization Gauges

Anomalously high residual collector current is observed with a Bayard-Alpert ionization gauge after the gauge has been exposed to a relatively high pressure gas which will chemisorb on the grid of the gauge. The evidence indicates that the principal portion of the anomalous residual current results from the subsequent release of the adsorbed species as high velocity ions. A small fraction of the fast ions collide with the collector resulting in a positive charge flow from the grid to the collector which is pressure independent. The more strongly chemisorbed gases are found to replace those which have been previously adsorbed. Oxygen results in the largest and most persistent anomalous residual current.