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Homework Help: Nuclear physics - number of nucleons on surface?

  1. May 22, 2008 #1
    1. The problem statement, all variables and given/known data

    For a nucleus of A=220, estimate very roughly how many nucleaons would be at the surface.

    2. Relevant equations

    R0=1.5 x 10-15

    r=A1/3 x R0

    3. The attempt at a solution

    Using the formulas, I calculated R to be 7.2441729 x 10-15

    The book says that the number of nucleons at the surface and the total number of nucleons has a ratio of ~1/r

    1/r= 1.3804 x 1014

    I tried the following:

    1.3804 x 1014 = 220/x

    which didn't make sense...

    what am I doing wrong?

  2. jcsd
  3. May 22, 2008 #2


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    I think the key here is 'very roughly'. You have a big sphere made of 220 smaller spheres. Roughly, what's the volume of that sphere in terms of the radius of the smaller sphere. What's the total area of that sphere? Each smaller sphere exposes, roughly, pi*r^2 of outer surface area. How many are there? Roughly.
  4. May 23, 2008 #3
    so I could set a volume of a sphere as 220, solve for r, and then find the surface area based on that?
  5. May 23, 2008 #4


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    Yes, then use the area to estimate the number of spheres with volume 1 on the surface. I think that's what they're after. It's certainly a 'rough estimate'.
  6. May 23, 2008 #5
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