CsI as a High-Gain Secondary Emission Material

Since Alvarez and Cone suggested transmission-type electron multipliers for use in high-speed counting systems, L most of the work on these devices has made use of KC1 for the high gain material in bulk density 2,3,4,5 as well as low density 6,7 form. During a study of low density dynodes for use in direct relativistic particle detection systems, f3,9,10 we have observed some interesting high-gain properties of CsI. It is the purpose of this letter to report some preliminary data on CsI (both bulk density and low density) as a high-gain secondary emitting material. Dynodes were prepared by evaporation in a diffusion-pumped vacuum system from MO "dimple" boats onto 1000 a self-supporting A1203 substrates with a 500 8 thick overlayer of Al. Bulk density dynodes were deposited at a pressure of N 1 x 10 -6 Torr. Low density dynodes were evaporated in a 4 Torr atmosphere of argon onto room temperature substrates spaced 2 inches from the boat.