On the Ageing Effect in the Mobility of Positive Gas Ions

Abstract

Mobility of positive ions of air immediately after formation has been found by Erikson, using a modified Zeleny method, to be much higher than the normal value. This result has been verified by the author using the alternating potential method. Ions formed in an ante-chamber by $\alpha$-rays from polonium were driven by a weak auxiliary field into the measuring chamber where the mobility was determined by the use of an alternating field of 1,800 to 3,600 cycles and of variable strength. Pure dry air was used at a pressure of 30 mm. When the auxiliary potential was 1.5 volts the measured mobility was normal but when the potential was 3.0 volts or more the mobility rose to 1.80 cm./sec./volt/cm., indicating that the ions entered the measuring chamber before they were aged. The time required for the ions to age or reach the normal condition is estimated to be between 1/75 and 1/120 of a second.