Question about Photoelectric Effect versus Compton Scattering.

In summary: So the higher-energy photons are more likely to just cause the electron to recoil, rather than ejecting it.
  • #1
uart
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In the context of interaction of photons (with energies from around visible light and upwards) and the electrons of solid matter. I've read that at the lower energy levels that the photoelectric effect is more likely to occur during such an interaction and that Compton scattering is more likely for higher photon energies like x-rays. (... and pair production at even higher energies).

I was just wondering why this is. Looking at it from a simplistic point of view I would have expected the opposite. That is, I would have expected that the higher energy photons would have been more likely to completely knock an electron out of the solid (PE effect) and that the lower energy photons would have been more likely to just make the electrons recoil as in Compton scattering.

Any simple explanations?
 
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  • #2
The photoelectric effect involves the electron absorbing the photon. Compton scattering involves the photon giving up part of its energy to the electron, since it has too much energy to get absorbed.
 
  • #3
Thanks mathman, I guess I was wondering why the electron can't just absorb the higher energy photon and and get ejected at with more KE.

Anyway it's making more sense to me now. So I'm guessing it's momentum considerations that makes it unlikely for a higher energy photon to give up all it's energy. If a high energy photon were to give all of it's energy to an electron then the electron would end up with more momentum than the photon could provide, so the lattice would have to make up the difference. Does this sound correct?
 
  • #4
uart said:
Thanks mathman, I guess I was wondering why the electron can't just absorb the higher energy photon and and get ejected at with more KE.

Actually, it can, but there's a limit to this where, after a certain level, the increase will not be noticeable.

As you increase the photon energy, you not only can get electrons close to the Fermi energy, you also start to probe deeper into the band structure. So not only are you getting higher energy photoelectrons, but you're also getting more low-energy electrons coming from deeper in the band. However, at some point, you will no longer get any more significant photoelectrons because the penetration depth of the photon is now longer than the escape depth of the photoelectrons. This is especially true for metals where the electrons trying to escape the metal have a higher probability of losing its energy via collisions with other conduction electrons. So when the penetration depth is longer than the electrons' escape depth, you'll not get any more electrons.

Zz.
 
  • #5
uart said:
In the context of interaction of photons (with energies from around visible light and upwards) and the electrons of solid matter. I've read that at the lower energy levels that the photoelectric effect is more likely to occur during such an interaction and that Compton scattering is more likely for higher photon energies like x-rays. (... and pair production at even higher energies).

I was just wondering why this is. Looking at it from a simplistic point of view I would have expected the opposite. That is, I would have expected that the higher energy photons would have been more likely to completely knock an electron out of the solid (PE effect) and that the lower energy photons would have been more likely to just make the electrons recoil as in Compton scattering.

Any simple explanations?
About photoelectric effect ZapperZ answered you, about Compton scattering, think that only for X-rays the photon starts to have enough energy to do something to the electron; for a photon in the visible range, a collision with an electron is something like a baseball colliding with a truck.
 

FAQ: Question about Photoelectric Effect versus Compton Scattering.

1. How are the photoelectric effect and Compton scattering different from each other?

The photoelectric effect refers to the emission of electrons from a metal surface when it is exposed to light of a certain frequency or energy. This process involves the transfer of energy from photons to electrons, causing them to be ejected from the metal. On the other hand, Compton scattering is a phenomenon where the energy and momentum of an incident photon is transferred to an electron, resulting in a change in the wavelength of the photon. In this case, the photon does not completely lose its energy, but only a portion of it is transferred to the electron.

2. What is the main difference in the mechanisms of the photoelectric effect and Compton scattering?

The main difference lies in the way energy is transferred. In the photoelectric effect, the energy of the photon is completely absorbed by an electron, causing it to be ejected from the metal. In contrast, in Compton scattering, the energy of the photon is partially transferred to an electron, resulting in a change in the wavelength of the photon.

3. How do the energies of the incident photons differ in the photoelectric effect and Compton scattering?

In the photoelectric effect, the incident photons must have a minimum energy threshold, known as the work function, in order to eject electrons from the metal surface. This energy must be equal to or greater than the binding energy of the electrons in the metal. On the other hand, in Compton scattering, there is no minimum energy requirement for the incident photons. However, the change in the photon's energy is dependent on the energy of the incident photon and the angle at which it scatters.

4. Which process is more sensitive to the properties of the material, the photoelectric effect or Compton scattering?

The photoelectric effect is more sensitive to the properties of the material, specifically the work function and the binding energy of the electrons. This is because the energy of the incident photons must match the binding energy of the electrons in order for them to be ejected. In contrast, Compton scattering is less sensitive to the properties of the material, as it is primarily dependent on the energy and angle of the incident photon.

5. Can the photoelectric effect and Compton scattering occur simultaneously?

Yes, the photoelectric effect and Compton scattering can occur simultaneously. In fact, both processes are commonly observed in experiments involving X-rays and gamma rays. The photoelectric effect dominates at lower energies, while Compton scattering becomes more dominant at higher energies.

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