What causes the peakes

  • Thread starter mythcism
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  • #1
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Can somebody explain in detail what causes the peakes.

this is carbon
Sec3135.gif


this is lead
Sec3150.gif


( Total photon cross section in carbon, as a function of energy, showing the contributions of different processes: t, atomic photo-effect (electron ejection, photon absorption); , coherent scattering (Rayleigh scattering—atom neither ionized nor excited); , incoherent scattering (Comp- ton scattering off an electron); , pair production, nuclear field; , pair production, electron field; , photonuclear absorption (nuclear absorption, usually followed by emission of a neutron or other particle).

thanks

(btw I am not really familiar with al these terms)
 

Answers and Replies

  • #2
1,159
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I am not sure if I am right but peak thresholds may correspond to resonance photon absorption by internal atomic shells in lead.
 
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  • #3
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The sharp peaks correspond the the k-shell binding energies of the electrons in atomic orbits, which is equal to about 13.6 Z2 eV (electron volts). This is the threshold for k-shell deep core photoejection.

Bob S
 
  • #4
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Thanks for the reply, but could you explain it in more detail please.
 
  • #5
4,662
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Thanks for the reply, but could you explain it in more detail please.
The sharp peaks in the photon absorption cross section are the result of the photon energy exceeding the 1s (k-shell) binding energy of electrons in atoms. This is approximately

EZ =~13.6 Z2 eV

As soon as the photon energy exceeds this value (sometimes referred to as the K edge), additional channels open up to absorb the photons. The bound electrons are knocked out by the deep core photoelection process.

Bob S
 
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  • #6
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But why does lead have 4 peaks and carbon 1. So what is every lead peak.
 
  • #7
4,662
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But why does lead have 4 peaks and carbon 1. So what is every lead peak.
The highest energy peak in lead is the K-shell edge (~90 KeV), the next lower should be the L-edge (~25 KeV), and the next the M-edge (~10 KeV). Lower Z elements may not have 1s, 2s, and 3s electrons.
Bob S
 
  • #8
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but it is this all about the s
But what is the most left peak at 200-600ev or something in that range.
 
  • #9
4,662
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but it is this all about the s
But what is the most left peak at 200-600ev or something in that range.
Here is the periodic table showing the x-ray absorption edges:
http://csrri.iit.edu/periodic-table.html
Click on carbon. The K-edge in carbon is about 284 eV.

The electron configuration in elements is

K-shell
1s(2)

L-shell
2s(2) 2p(6)

M-shell
3s(2) 3p(6) 3d(10) etc.,

where the number in ( ) is the number of electrons in a filled level.

Bob S
 

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