An explanation of the maximum in secondary electron emission from metals

It is well known that the curve plotted for ‘I s /I p : V’, where ‘I s ’ is the total secondary electrons corresponding to the primary electrons ‘I p ’ of energy ‘V’ volts, shows a flat maximum at higher values of ‘V’. The presence of this maximum is explained on the assumption that the rate of loss of energy of the primary electrons obeys the Thomson-Whiddington Law and the secondary electrons generated at various depths are absorbed by the target on their way out. The relation derived on this assumption shows the dependence of the value of the voltage, corresponding to this maximum, on the density of the metal as has been observed experimentally.