Final answer:
The photocathode emits electrons when stimulated by light due to the photoelectric effect, which are then multiplied through a series of dynodes in a photomultiplier tube, creating a detectable electrical signal.
Step-by-step explanation:
The photocathode in devices like the photomultiplier tube is responsible for converting the light output from a scintillator into an electrical signal. This process begins when light stimulates the photocathode, a thin metal layer commonly made of cesium and antimony compounds. The input phosphor light causes the emission of electrons due to the photoelectric effect.
The electrons ejected from the photocathode are then attracted to the next stage in the tube by a more-positive potential. As these electrons move from one dynode to the next, each with a successively higher potential, their number is multiplied. This multiplication of electrons at each dynode leads to an amplified electrical signal, resulting in a detectable output current that can be correlated with the energy deposited in the scintillator.