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What causes the peakes

  1. Oct 31, 2009 #1
    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)
     
  2. jcsd
  3. Oct 31, 2009 #2
    I am not sure if I am right but peak thresholds may correspond to resonance photon absorption by internal atomic shells in lead.
     
    Last edited: Oct 31, 2009
  4. Oct 31, 2009 #3
    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
     
  5. Nov 2, 2009 #4
    Thanks for the reply, but could you explain it in more detail please.
     
  6. Nov 2, 2009 #5
    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
     
    Last edited: Nov 2, 2009
  7. Nov 2, 2009 #6
    But why does lead have 4 peaks and carbon 1. So what is every lead peak.
     
  8. Nov 2, 2009 #7
    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
     
  9. Nov 2, 2009 #8
    but it is this all about the s
    But what is the most left peak at 200-600ev or something in that range.
     
  10. Nov 2, 2009 #9
    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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