Total Secondary Electron Emission from Thin Films of Sodium on Tungsten

The secondary emission yield has been determined for thin films of sodium on a polycrystalline tungsten base and compared with that obtained for a clean tungsten target over a range of primary electron energies of 100 to 1200 volts. The secondary emission yield showed a systematic increase as the work function of the surface was decreased by the addition o sodium. Measurements made as sodium was being evaporated off the tungsten showed that at no time did the secondary emission yield fall below that of clean tungsten. The work function was increased by forming an air film on a clean tungsten surface and the secondary emission was shown to decrease. This variation of secondary emission is in agreement with that found by other experimenters and predicted theoretically.