Why the photoelectric cross section decreases with the energy of the photon?

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Discussion Overview

The discussion revolves around the relationship between photon energy and the absorption cross section in the context of the photoelectric effect and photoionization. Participants explore why the absorption cross section decreases as photon energy increases, touching on concepts such as resonance and core-level photoemission.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants assert that higher photon energy allows for greater ionization potential, questioning why the absorption cross section decreases with energy.
  • One participant suggests resonance as a possible explanation, though this is challenged by others.
  • Another participant expresses skepticism about the claim that the absorption cross section decreases with photon energy, asking for references to support this assertion.
  • Concerns are raised about the accuracy of Wikipedia as a source for understanding the photoelectric effect and its relation to core-level photoemission.
  • A participant distinguishes between the photoelectric effect and core-level photoemission, indicating that standard photoemission typically involves visible to UV light probing the conduction band.
  • One participant mentions that if the photon energy is just sufficient to eject an electron, the likelihood of ejection decreases as energy increases, suggesting a complex relationship.

Areas of Agreement / Disagreement

Participants do not reach consensus on the relationship between photon energy and absorption cross section. Multiple competing views are presented, particularly regarding the definitions and contexts of the photoelectric effect and photoionization.

Contextual Notes

There are limitations in the discussion, including missing assumptions about the definitions of terms like "photoelectric effect" and "photoionization," as well as unresolved mathematical or conceptual steps regarding the absorption cross section.

wdlang
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the higher the energy of the photon, the more powerful it can ionize an atom

but why then the absorption cross section decreases with the photon energy?
 
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Resonance?
 
I'm not aware that it does? Where is this written?

More photon energy simply means more kinetic energy of the ejected electron, from what I can remember.
 
mathman said:
Resonance?

not a resonance
 
wdlang said:
the higher the energy of the photon, the more powerful it can ionize an atom

but why then the absorption cross section decreases with the photon energy?

You need to learn to provide references.

Zz.
 
ZapperZ said:
<Sigh>

Please cite specifically where it says "... absorption cross section decreases with the photon energy..."

Zz.

see Cross section
 
wdlang said:
see Cross section

That is core-level photoemission. It is no longer the same "photoelectric" effect that is characterized by the Einstein equation. Notice the energy of the photon being used. The standard photoemission is done using predominantly visible to UV light that probes the conduction band, not core levels.

BTW, as someone who has done photoemission spectroscopy extensively, I would use this particular entry in Wikipedia as the poster child why someone should NOT use Wikipedia to learn from.

Zz.
 
  • #10
ZapperZ said:
That is core-level photoemission. It is no longer the same "photoelectric" effect that is characterized by the Einstein equation. Notice the energy of the photon being used. The standard photoemission is done using predominantly visible to UV light that probes the conduction band, not core levels.

BTW, as someone who has done photoemission spectroscopy extensively, I would use this particular entry in Wikipedia as the poster child why someone should NOT use Wikipedia to learn from.

Zz.

i know this

i have in mind the photoelectric effect of atoms not metals
 
  • #11
wdlang said:
i know this

i have in mind the photoelectric effect of atoms not metals

Then please look up "photoionization". The topic of this thread is now no longer accurate.

Zz.
 
  • #12
wdlang said:
not a resonance

My recollection is vague, but from what I remeber if the photon energy is just enough to kick the electron out of the atom, the electron is more receptive. As the photon energy gets higher it is less likely to happen. The following may help.

https://netfiles.uiuc.edu/mragheb/www/NPRE%20402%20ME%20405%20Nuclear%20Power%20Engineering/Gamma%20Rays%20Interactions%20with%20Matter.pdf
 
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