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Finding the shortwavelength limit of the white spectrum

  1. Feb 20, 2007 #1
    1. The problem statement, all variables and given/known data

    I am trying to find the short wavelength limit ( and consequently plankcs constant) of the white or bremstrahlung spectrum. The data came from the bragg scattering of x-rays produced from a copper anode scattered of a NaCl crystal. The graph is counts vs degrees. The spectrum is from 11-30ยบ on a 2-theta scale. There were two trials for the white spectrum, one of 20 KeV x-rays and the other of 30 Kev x-rays. The shortwavelength limit is defined as the intersection of the x-axis.

    One of the main equations is,

    [tex] hf\; =\; h\left( \frac{c}{\lambda } \right)\; =\; \mbox{E}\; =\; 20\; KeV [/tex]

    2. Relevant equations

    The problem is that my data is in counts vs degrees, not counts vs wavelength. I need my x-axis to be in wavelength, not the recorded degrees. I am not sure how to convert it.

    3. The attempt at a solution

    I am a bit clueless on this one. I tried using 2d*sin(theta) = n*lambda to convert the degree axis into a wavelength axis, I knew it would be wrong iand sure enough, I got a planck's constant of five magnitudes off.
  2. jcsd
  3. Feb 20, 2007 #2
    Surely someone must know! Or is it too hard? :(
  4. Feb 20, 2007 #3
    If you have a rotating crystal and plot signal vs. rotation angle, then by knowing theta (incident angle relative to the crystal surface) and the crystal 2d spacing you can calculate signal vs. lamda from lamda = 2d*sin(theta). Perhaps you referenced the angle to the crystal surface normal instead?
  5. Feb 21, 2007 #4
    D'oh! Sorry for taking your time, my initial approach was correct but I must have done some silly calculator error.
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