Shot Effects of Secondary Electron Currents

The shot effect of secondary electron currents from plates of triode tubes was measured at 105 cycles. Calculations of the electronic charge from shot effects of temperature-limited primary currents, to check the method, agreed with Millikan's value within 1 percent. Measurements were made on five tubes having different secondary emissivities. The average number of secondaries per primary electron, ω, ranged from 1 to 4.5. The variation of ω with energy of the primaries is shown to agree qualitatively with existing theory. In every case the shot effects of both grid and plate currents were measured. Campbell's general expressions for the shot effect of secondary emission plate currents were extended to grid currents. From the observed differences between grid and plate shot effects it is concluded that secondary emission and primary impact are simultaneous within 10−6 second or less. The large shot effects found at high values of ω are correlated with the fluctuations of ω from one impact to another. A qualitative analysis of secondary emission processes shows that, from these data, information can be obtained as to the number of reflected primary electrons and the number of primaries which emit no secondaries. The results obtained are in reasonable agreement with data obtained by other methods.