In a photomultiplier tube, one or more electrons are emitted from a photocathode and accelerated towards a polished metal electrode (called a dynode). They hit the electrode surface with sufficient energy to release a number of electrons through secondary emission. These new electrons are then accelerated towards another dynode, and the process is repeated several times, resulting in an overall gain ('electron multiplication') in the order of typically one million and thus generating an electronically detectable current pulse at the last dynodes.