Secondary Electrons from Iron

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Abstract
Secondary electron emission from iron as a function of energy of primary electrons, 0 to 300 volts.—Curves showing ratio of secondary to primary electron current as a function of primary velocity were obtained with three forms of apparatus. Two have been previously described. The limiting curves obtained after red-heat treatment of samples of electrolytic Fe having very large crystals, and of chemically pure Fe obtained from Kahlbaum were similar to those obtained for a film of Fe deposited by evaporation. The curves all have sharp maxima at 1.2 and 7.0 volts with minima at 3.7 and 12.0 volts, and a less prominent maximum and minimum at 10.0 and 9.0 volts, respectively. Of several metals tried, Fe is the only one, in addition to Cu, for which such sharp maxima and minima have been obtained. Potentials corresponding to positions of the maxima are interpreted as critical potentials. A steady upward trend of the curve begins at 12.0 volts, which is interpreted as being due to ionized electrons. Slight changes in slope of the curve at higher potentials were observed but these varied with conditions, and hence are taken to have no real significance.