What is the difference between photoelectric effect and secondary emission in photo multiplier tubes? In other words, why the difference between the energy of the incident photon and the work function of the material (in photoelectric effect) turns into kinetic energy to the released electron, while this is not the case in secondary emission ?

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    $\begingroup$ Did you read the Wikipedia articles I just linked in your question? $\endgroup$ – ACuriousMind Apr 7 '15 at 14:27
  • $\begingroup$ Yes ,sir I have already went through all that stuff but I did not find a clear distinction between the two effects. Thanks anyway. $\endgroup$ – Mohamed Goda Apr 7 '15 at 16:15
  • $\begingroup$ Well, what is the result of applying conservation of momentum when a primary electron generates (several) electrons at the next plate? $\endgroup$ – Carl Witthoft Apr 7 '15 at 18:35
  • $\begingroup$ Carl,My question is why several electrons are released per one incident electron? why it is not one-to-one correspondence like that in photoelectric effect? $\endgroup$ – Mohamed Goda Apr 7 '15 at 22:18

The difference you are looking for is in the particle energy. The photon energy for visible light is about $3\,\mathrm{eV}$ (electron-volt), just enough to kick one electron from photocathode. In the photomultiplier, this electron is accelerated towards dynodes with high voltage. If it is $1000\,\mathrm{V}$, then the electron gains kinetic energy of $1000\,\mathrm{eV}$, thus being able to release much more secondary electrons on impact.

  • $\begingroup$ If I could increase the energy of the incident photon this increase does not lead to more electron being released ,instead it just gives more kinetic energy to the released electron. On the other hand increasing the energy of the incident electron lead to more electron being released. So WHY IS THAT? $\endgroup$ – Mohamed Goda Apr 8 '15 at 8:43
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    $\begingroup$ @MohamedGoda At such energies, the incident electron will probably not give all its energy at once to the first released electron. He will have the opportuntity to release other electrons after having shed a part only of its energy. This is different with a photon that will be absorbed and will transfer all its energy at once. $\endgroup$ – Martigan Apr 8 '15 at 8:48
  • $\begingroup$ @MohamedGoda: my guess would be that the photon is absorbed upon interaction with matter, whereas electron remains and can interact further. $\endgroup$ – gigacyan Apr 8 '15 at 16:51
  • $\begingroup$ @gigacyan Compton Scattering falsify your guess. You know in Compton scattering experiment the incident photon is not completely absorbed and it can interact further $\endgroup$ – Mohamed Goda Apr 8 '15 at 17:25
  • $\begingroup$ @MohamedGoda but then the photon would be able to travel further and release more electrons. Or, do you mean that the photon ejects one electron at a time, contrary to the electron? $\endgroup$ – gigacyan Apr 9 '15 at 15:10

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