Determination of the Probability Distribution of the Number of Secondary Electrons

It is shown that the probability distribution, p(i), of the release of i slow secondary electrons after the incidence of a primary particle of any sort (such as electrons, photons, ions etc.) can be determined by the use of a multistage electron multiplier (EM). The method is based on the idea of using the EM merely as a tool to amplify to an easily measurable level the effect produced by the process to be investigated. First, the single electron response of the EM, the pulse height distribution, ¿(x), in the output, is experimentally determined. Next, the pulse height distribution, F(x), is taken when the secondary electrons of the process to be measured enter the input. In the process of calculation of p(i) from ¿(x) and F(x) the moments of the distributions are used. This has the advantage that the successive calculation of the first few moments of p(i) gives information (average, variance, skewness etc.) which in many cases is of primary interest. Extension of the calculation to higher moments allows the determination of p(i) via the combinatorial moments. Experimental data taken for an EM with silver-magnesium dynodes show that the secondary emission curve for 230 ev primaries is somewhat broader than a Poisson distribution.