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Homework Help: Bragg's Angles for X-Ray

  1. Jan 24, 2017 #1
    1. The problem statement, all variables and given/known data
    The Spacing between the Na and Cl atoms in table salt (NaCl) is ##d=2.82x10^{-10}m##, which was first deduced from Bragg scattering. For an experiment where X-rays of energy 20 eV are produced, what are the corresponding Bragg angles below ##90^{\circ}## for scattering from a large crystal of table salt?

    2. Relevant equations
    Bragg's Law: ##2dsin(\theta)=n\lambda##

    3. The attempt at a solution
    ##sin(\theta)=\frac{n\lambda}{2d}##
    ##\lambda = \frac{hc}{E_{photon}}##
    ##\theta = sin^{-1}(\frac{nhc}{2dE})##
    ##\theta = sin^{-1}(\frac{n*1240eV\dot nm}{2*0.282nm*20eV})##
    ##\theta = sin^{-1}(n*109)##

    but this isn't within the domain of arcsin. So are there just no Bragg's angles here? Or is there a different energy that I'm using rather than 20 eV?
     
  2. jcsd
  3. Jan 24, 2017 #2

    Charles Link

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    Homework Helper
    Gold Member

    I believe your calculations are correct. Perhaps someone else can also check the numbers, but I think the x-ray energies need to be more like 20 keV.
     
  4. Jan 25, 2017 #3

    mjc123

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    Science Advisor

    Definitely in the keV region. From memory, Cu Kα, a common source, is around 8 keV.
     
  5. Jan 25, 2017 #4
    After turning in the work today, the professor mentioned there was a typo in the book and he failed to email us to tell us that before hand. It was in fact supposed to be 20 keV.
     
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