The Apparent Transmission of Low Velocity Electrons Through Aluminum Foil

Abstract

Apparent transmission of low velocity electrons through aluminum foil.—Electrons were accelerated from a tungsten filament to a foil $F.\mathrm{}0003\mathrm{}$ cm thick behind which at a distance of 1 mm was a nickel receiving plate $P$ connected to an electrometer. The ratio of electron current reaching $P$ to that reaching $F$ showed a maximum at about 8 volts primary energy though the position of this maximum shifted somewhat. By using a retarding potential on $P$, all the electrons reaching $P$ were found to have velocities less than 10 volts (maximum number at about 2 volts) even when the primary bombarding electrons had a velocity of 1600 volts. Apparently, aluminum shows a transparent atom effect for slow electrons similar to that observed in rare gases. In addition to slow speed secondaries, the electrons reaching $P$ include photo-electrons from the back side of $F$ due to x-rays produced by the primaries. The effect with two foils was only ${10}^{-4\mathrm{}}$ times that through one and was probably largely photo-electric. The third foil cut down the plate current by an additional factor of 1/10.