Shot Effect of the Emission from Oxide Cathodes

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Abstract
Experimental procedure in the study of fluctuations in the space current of a thermionic emitter is outlined. A new method of measuring shot-circuit impedance is introduced. Conditions under which the observed fluctuations may be applied to determine the electronic charge are pointed out. A method is described whereby the frequency of oscillating circuits used in this investigation may be determined and controlled. An investigation has been made of the fluctuations associated with the emission from barium-strontium oxide cathodes, particularly in the space charge region. The presence of positive ions in the emission from oxide coatings has been experimentally verified. These positive ions moving in an electron space charge cause abnormally high shot-fluctuations in an aperiodic circuit at high amplifier frequencies. The characteristic fluctuations associated with the emission from oxide cathodes have been reproduced in a vacuum tube of special design in which positive ions from an independent Kunsman potassium ion emitter interact with electron space charge about a metal emitter. This is taken as evidence that the same process goes on in the emission from barium-strontium oxide cathodes. Some results obtained in a study of the shot effect of films evaporating from a tungsten wire are included.