Secondary electron emission measurements for 3-20 /spl mu/m aluminum foils using a 70 keV, DC electron beam

Abstract

Summary form only given. This paper is a presentation of experimental results and Monte Carlo calculations of 20-70 keV electron penetration through thin aluminum foils. Transmission ratios as well as energy characteristics of secondary electrons are measured for 3-20 mum thick foils. Parameter space and analysis is directed towards fulfilling requirements for a radio isotope micro-power sources (RIMS) energy conversion device. RIMS are enabling technologies for miniature electrical and mechanical devices. One RIMS concept involves the conversion of low numbers of high energy electrons from a beta emitter into large numbers of low energy electrons. These low energy electrons charge a metal plate which in turn provides power for the miniature devices. The conversion is accomplished by placing thin foils or films in the path of the high energy electrons. Film material and thickness are designed to maximize the secondary electron emission. For supplying the high energy primaries in our experiment, a DC electron gun was designed. A tungsten filament was utilized with two optics for adjustment of beam focus and current. The current was adjustable from zero to 500 nA with 1 nA resolution. This cathode assembly was biased from zero to -70 kV for control of the energy of the primary electrons. In this paper, we will show the design characteristics and the beam classification of our electron gun. Also, we will show that for a given foil thickness, there is a discrete peak in the low-energy secondary electron emission. In addition, there is not a greater than unity conversion from high energy primaries to low energy secondaries