The Absorption Coefficient for Slow Electrons in Thallium Vapor

The absorption coefficient $\alpha$ has been observed by sending a beam of electrons through thallium vapor and measuring the decrease in intensity of the beam as a function of the pressure of the vapor. $\alpha$, plotted as a function of the velocity of the electrons, decreases rapidly to a minimum of 15 at 1.4 volts, rises less rapidly to a maximum of 51 at 4.5 volts, and then slopes off gradually to 20 at 100 volts.