What are dynodes and how do they amplify electrons in a photomultiplier tube?

In a photomultiplier tube, dynodes are a series of additional electrodes positioned after the photosensitive cathode. They play a critical role in amplifying the signal generated by the photoelectric effect.12

When light strikes the cathode, it releases electrons that are accelerated toward the first dynode. Each dynode is maintained at a successively higher positive potential, which attracts the electrons emitted by the previous stage.12

The amplification process occurs through secondary emission:
* When an electron strikes a dynode, it causes the surface to emit several additional electrons.1
* These new electrons are then accelerated to the next dynode, where the process repeats, multiplying the total number of electrons at each stage.12
* By the time the electrons reach the final dynode, the original signal has been enormously amplified—sometimes by a factor of up to 1,000,000—allowing the device to detect even extremely weak light sources, such as a single photon.12