Ejection of Only one electron by a Photon in the Photoelectric effect

  • #1

Main Question or Discussion Point

Hi
I am surprised to know why only one photon in photoelectric effect ejects one electron only. What if a high energy photon (not necessarily x-ray or gamma ray, which may cause Compton effect or pair production)hits the metal, say it has energy double or triple of that of the work function? Why does not it eject two or more electrons?
Please help.
Regards
 

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  • #2
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That process is possible but very unlikely. In general reactions get less likely the more particles have to be involved.
 
  • #3
Please some more information.
Regards
 
  • #4
ZapperZ
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Hi
I am surprised to know why only one photon in photoelectric effect ejects one electron only. What if a high energy photon (not necessarily x-ray or gamma ray, which may cause Compton effect or pair production)hits the metal, say it has energy double or triple of that of the work function? Why does not it eject two or more electrons?
Please help.
Regards
First of all, an energetic photon may cause more than one electron to be ejected, but NOT via the photoelectric effect. The Auger process can certainly result in more than one electron being ejected per photon.

But for the photoelectric (or more accurately, a photoemission) process, the entire energy of the photon is absorbed on one shot. There is no partial absorption. This is, by definition, the photoemission process. If the process involves anything else, then it is called something else.

Zz.
 
  • #5
First of all, an energetic photon may cause more than one electron to be ejected, but NOT via the photoelectric effect. The Auger process can certainly result in more than one electron being ejected per photon.

But for the photoelectric (or more accurately, a photoemission) process, the entire energy of the photon is absorbed on one shot. There is no partial absorption. This is, by definition, the photoemission process. If the process involves anything else, then it is called something else.

Zz.
Thanks indeed for your kind reply. To my understanding Auger process involves ionization of an atom due to emission of inner electron after being hit by high energy photon. The vacancy thus created is filled by some electron from higher orbits. Another photon thus created hits another electron and kicks it out. In all this chain, still one photon knocks out one electron. This is what I want to know. Even in Compton effect, we see same thing happens. Please spare some more time for my query.
High regards.
 
  • #6
ZapperZ
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Thanks indeed for your kind reply. To my understanding Auger process involves ionization of an atom due to emission of inner electron after being hit by high energy photon. The vacancy thus created is filled by some electron from higher orbits. Another photon thus created hits another electron and kicks it out. In all this chain, still one photon knocks out one electron. This is what I want to know. Even in Compton effect, we see same thing happens. Please spare some more time for my query.
High regards.
But that original one photon that entered the material has now kicked out more than one electron. So that in itself has already answered your original question. But now comes the details, because, for example, how would we know that an Auger process took place?

This is where one has to look at the details of the emitted electron spectrum. The Auger process has a distinct spectrum where by it actually gives you info about the core level states. A "compton scattering" does not, because the compton spectrum is typically broad!

Besides, there's another important issue here. When an energetic electron bumps into another electron, this is a "lossy" process in terms of energy of the original electron. In fact, an electron that already has enough energy to escape a material will tend to lose that energy quite easily if it bumps into another electron before it escapes the material. This is why metals are usually poorer photocathodes than semiconductors, because metals have more free electrons than semiconductors. So a "compton process" inside a solid is often detrimental to the emission of electrons from that solid.

Zz.
 
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