Photomultiplier (PM) Tube:

A photomultiplier tube, consists of a series of electrodes, known as dynodes. The voltage of successive electrodes is managed 50 to 90 volt more positive than the previous one. While a radiation falls on the cathode an electron is emitted from it. This is accelerated towards the next photoemissive electrode through the potential difference among the two. Here, it releases several more secondary electrons. Those, in turn are accelerated to the next electrode whereas each secondary electron releases more electrons. The procedure continuous upto about 10 levels of amplification. The last output of the photomultiplier tube provides a much larger signal than the photocell.