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Radiation physics, need help

  1. Mar 26, 2008 #1
    The problem: 1000 photons all having an energy of 100 keV hits a copper plate 2 mm thick. How many of these photons can be detected on the other side by a detector that absorbs all radiation? The incident angle is 30 degrees with respect to the plane of the copper plate.

    If the angle had been 90 degrees I would have had no problem calculating this -- it would just have been N = N0*e^(mu*L), where N0 is the number of incoming photons, mu the linear attenuation coefficient, and L the thickness of the copper plate. But now that it says 30 degrees, I'm out of ideas.
  2. jcsd
  3. Mar 26, 2008 #2
    The path length is greater since the beam is not striking the face at 90 degress, just figure out the correct path length through the 2mm thick slab.
  4. Mar 26, 2008 #3
    Thanks. I forgot that the photons are assumed either to be absorbed fully by the material, or to pass through without any interaction. So L should be be replaced by L'=4 mm, right? (That is, L'= 2mm/sin30).
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