Secondary Emission of Nickel-Barium Mixtures and Rhenium When Bombarded by Electrons with Energies from 50 to 8000 Electron-Volts

Abstract

The experimental tube contains a contamination-free gun which directs an electron beam at normal incidence onto a small thin sheet target which may be heated by conduction. The target is located at the center of a conducting sphere to permit a measure of the secondary current, and also of the energy distribution of the secondary electrons by means of the retarding potential method. The maximum value of δ, the secondary emission ratio, for a cast alloy of nickel containing 1.5 percent barium is 2.8 and occurs at 800 to 900 volts after a critical amount of previous heat treatment of target. The value of δmax increases with heat treatment of target, subsequent to baking of tube, to the above value and then decreases with further heating. For the critical condition the value of δ above 4000 volts is sensitive to the amount of previous electron bombardment of the target. A δmax of 1.3 for rhenium after thorough out-gassing was obtained at 900 volts. The most probable energy of low speed secondary electrons from rhenium is approximately 5 ev.