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Xray Imaging Intensity

  1. Jun 18, 2014 #1
    1. The problem statement, all variables and given/known data

    Imagine a 10 cm thick slab of flesh. If your x-ray imager can reliably identify a 5% change in intensity from one location to another in an image, what is the smallest diameter bone you are going to be able to make detect in your x-ray image?

    Absorption length of bone: 0.017 m

    2. Relevant equations


    3. The attempt at a solution

    I tried letting 0.05=e-μx letting 0.017m be μ. The correct answer is supposed to be 1.3 mm but I can't seem to get that.
  2. jcsd
  3. Jun 18, 2014 #2


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    1. going from 1 to 0.05 is a change of 0.95. Consider going from I = 1 to I = 0.95.
    2. μx must have no dimension, otherwise you can't exponentiate it. your exponent has the wrong dimension....
    3. What is the definition of absorption length in your context ? I = I0 / e or I = I0 / 2 ?
  4. Jun 18, 2014 #3
    I set it up so that 0.95=e-μx trying to let μ=1/0.017 so that x could be in meters without having units in the exponent. That did not work either when trying to solve for x. There are no explanations for these practice problems and I have only ever heard the term "absorption coefficient" not absorption length, which is why I'm confused.
  5. Jun 18, 2014 #4


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    "Did not work either" means you found 0.017 m * ln(0.95) = 0.00087 m ?

    I agree the most common maeening for absorption length is length over which I = I0 / e.

    It's just because your 'right' answer corresponds to 0.017 m * 2log(0.95) that I asked for this context.

    I can't think of anything else to help you with at this moment (bedtime+3h).....:frown:
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