Secondary electron multipliers (SEV) exploit the effect that certain materials emit secondary electrons when struck by electrons. Depending on the material, the acceleration voltage and the angle of entry of the electrons into the electrode material, the number of escaping secondary electrons exceeds the number of impacting electrons many times over. This is related to the number of free and light-bound electrons and to the penetration depth of
the electrons.Corresponding multiplier electrodes are called dynodes and have multiplication factors between 3 and 10. This means that an impacting electron emits between three and ten secondary electrons.
Secondary electron multipliers consist of several dynodes arranged in series, each of which is connected to an accelerating voltage
The individual accelerating voltages have increasing potential and generate electrostatic fields between the dynodes with which the secondary electrons are accelerated from one dynode to the other.
lier The multiplication effect of the secondary electrons cumulates from dynode to dynode. Forexample, if the multiplication factor per dynode is two, then the multiplication at 10 dynodes (2exp10) is a thousandfold, and at a factor of four (4exp10) it is already a millionfold.