Spectres d'impulsions à ⪡un photoélectron⪢ des photomultiplicateurs

Abstract

Analysing the histogram of anode pulse amplitudes allows a discussion of the hypotheses that have been proposed to account for the statistical processes of secondary multiplication in a photomultiplier (PM 56 DVP): a Poisson process, as was suggested by Lombard and Martin (1961), or a Polya process, as suggested by Prescott (1966). Comparison of experimental single-electron pulse spectra with calculated theoretical spectra is first performed by means of moment analysis, from which fractional variance, skewness (a measure of the asymmetry of the distribution), and excess of kurtosis (a measure of the sharpness of the peak and the extent of the tails, as compared with those of a Gaussian distribution), are deduced; then, by directly comparing the shapes of the spectra and minimizing the area between them. On the whole, this study on a focussed dynodes PM makes it clear that though a Polya process is a better approach to reality than a Poisson process, the gain distribution which it leads to does not correspond to the experimental spectrum. A better accord is obtained on assuming a dynode distribution including, in a first approximation, two Poisson distributions of distinct mean value and expressing an inhomogeneity of the secondary multiplication gain value different from that imagined by Prescott.