Secondary Electron Emission from Tungsten, Copper and Gold

By a null method of high precision, previously described, the secondary electron emission from tungsten, copper and gold surfaces bombarded by an electron stream has been measured and the ratio $\frac{I_1}{I_2}$ of secondary current to primary current plotted as a function of the velocity of the primary electrons. The maximum values reached by the ratio $\frac{I_1}{I_2}$ were as follows: 1.45 for tungsten at 700 volts, 1.32 for copper at 240 volts, 1.14 for gold at 330 volts. Tungsten showed fairly satisfactory critical potentials at 11.0, 17.1, 25.2, 29.3, 40.5, 46.0, 89.5, and 271.5 volts. Copper showed breaks at 7.8, 12.6, 16.8, 19.5, 23.8, 39.0, 56.9 and 73.5 volts, the first two being marked by very definite minima. Gold indicated critical potentials at 15.5, 21.0, 23.2, 31.5 and 43.7 volts. Comparison of these potentials with soft x-ray levels does not lead to a definite conclusion as to the relation between the two.