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I X-ray Spectrometer lab

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  1. May 28, 2013 #1
    Hey!

    I'am doing a X-ray spectrometer lab, need some help regarding the absorption of x-rays by matter. one simple question, does material with higher atomic number stop more x-rays?

    I have following measurement values:
    no filter, 6k impulse rate/s
    50 Sn, 111 impulse rate/s
    30 Zn, 3173 impulse rate/s
    29 Cu, 2735 impulse rate/s
    28 Ni, 2829 impulse rate/s

    the filters has the same thickness.
    its kinda strange when Ni stop more x-ray compare to Zn, since Zn has bigger atomic number compare to Ni. But with Sn i can see a big absorption. can anyone give me a explanation?

    thanks
     
  2. jcsd
  3. May 28, 2013 #2

    davenn

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    Hi Aseth
    welcome to PF


    its not the absorption that you are looking at its the re-emission of an Xray.....

    When I was doing this in my university geology studies this is what I was taught....
    when the sample is targetted with X-rays, an inner shell electron is lost due to that excitation from the X-ray source. An electron from an outer shell will drop to that inner position and loose energy as a result.
    The energy lost is the emission of a X-ray photon. This photon has a wavelength ( energy signature) that is specific ( characteristic) for that element.
    You are recording those emitted X-ray photons to determine the elements present in the sample. Some elements will have multiple peaks.

    You should have charts in the lab that will show the peaks for all the elements

    We also did XRD in the lab as well... X-Ray Diffraction

    From Wikipedia,

    X-ray scattering techniques are a family of non-destructive analytical techniques which reveal information about the crystal structure, chemical composition, and physical properties of materials and thin films. These techniques are based on observing the scattered intensity of an X-ray beam hitting a sample as a function of incident and scattered angle, polarization, and wavelength or energy. Note that X-ray scattering is different from X-ray diffraction, which is widely used for X-ray crystallography.

    There were several nasty pictures on the wall of the lab showing what happens to the fingers of careless people when using the XRD equip.


    hope that helps
    Dave
     
    Last edited: May 28, 2013
  4. May 28, 2013 #3

    davenn

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    since I'm into geology, not particle physics.

    I never did understand where that "lost" electron from the inner shell went to ?
    is it being ejected by the X-Ray bombardment or something else ?

    hopefully some one else on here can answer that question for me :)

    Dave
     
  5. May 30, 2013 #4

    davenn

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    can any of our particle physics experts help with my query please ?

    thanks
    Dave
     
  6. May 30, 2013 #5
    Two things that you should consider:

    (1) The foils may be of the same thickness, as you say, but the atomic density of Ni is higher than Zn.

    (2) The X-ray absorption depends on photon energy (see link below for data). For each element, there are certain energy regions at which absorption is rather high. If you are using Cu K X-radiation, it will be able to excite Ni K electrons but not those of Zn, which lie at deeper energies. Thus Ni could absorb more X-rays than Zn for this reason.

    http://physics.nist.gov/PhysRefData/XrayMassCoef/tab3.html
     
  7. Jul 23, 2015 #6
    Why can't Cu K alpha eject electrons from atoms of the sample in XRD?
    As everyone knows, Al K alpha photon with 1486 eV energy is used for XPS to remove electrons from core levels. My doubt is why cant Cu K alpha photon with 8000+ eV do that?
     
  8. Jul 23, 2015 #7

    ZapperZ

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    Just so you know, "particle physicist" don't work with these things. You need someone with chemistry, material science, or condensed matter physics background.

    Just so I know which one you are referring to, is your experiment an x-ray fluorescence measurement? If it is, then depending on the energy and the material, the first electron is either promoted to the outer bands (or conduction band), or it is liberated. If it is liberated, some instruments will make use of such electrons as additional measurement, such as in Auger spectroscopy.

    Zz.
     
  9. Jul 23, 2015 #8

    davenn

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    wow a 2 yr old thread resuscitated back to life

    for future reference, @madhusoodan, its better to start a new thread than bring back a very old one


    Dave
     
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