electron multiplier

An electron multiplier is a detection device inside the vacuum of the mass spectrometer that converts the arrivals of ions at its front dynodes into a detectable, amplified electron current at the back lead of the device. The overall gain (signal out/signal in) can be as high as 104–108. Positive ions exiting  from the mass analyzer impact the first dynode surface, and the impact causes the release of several electrons, which are then accelerated through a potential to the next electrode. There, each electron impact causes the release of several secondary electrons, which are accelerated into the next dynode for a repetition of the impact–release process. A cascade of electrons is produced, generating a current that is further amplified and then sampled by an analog-to-digital converter  to be recorded by the data system.