Secondary electron emission from mercury

Abstract

Following a suggestion by Bronshtein and Fraiman that the total secondary emission coefficient for solid mercury measured by Brophy was too low, a programme of research was initiated, and a series of measurements produced evidence that there are two mechanisms for contamination of a mercury target in a measuring tube evacuated by a mercury diffusion pump. The first, which lowers the values of the total coefficient, is thought to be water vapour on the surface of the target. The second, which raises the value, may be backing pump oil contamination. A system has been devised with which it is possible to control and eliminate these contaminants. The results obtained for the total and partial coefficients for pure, uncontaminated samples agree with those predicted by Bronshtein and Fraiman from their study of regularities in the behaviour of the coefficients with atomic number. The lower values of Brophy are shown to be due to contamination. There is no change in the values of the coefficients as mercury solidifies. However, starting from room temperature, the values of the total and partial coefficients have been found to fall and rise respectively as the temperature is lowered.