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Homework Help: Classical scattering off a paraboloid

  1. Dec 31, 2007 #1
    1. The problem statement, all variables and given/known data
    Particles are scattered (classically) from a paraboloid shape. The surface is given by the relation:

    [tex] z = a \left(\frac{y^2+x^2}{R^2}-1 \right)[/tex]
    for x^2 +y^2 leq R^2 where a and R are constants. The particle is incident from z = -infinity with impact parameter s.
    Show that there a minimum angle below which there is no scattering occurs given by

    [tex] tan(\theta_{min}/2) = R/2a [/tex]

    where theta is the scattering angle.

    2. Relevant equations

    3. The attempt at a solution

    I found [itex]\tan(\theta/2) = R^2/2sa[/itex]. The problem implies that s cannot be greater than 1, which I fail to understand.

    I am not sure why the restriction "x^2 +y^2 leq R^2" was included. Maybe that has something to do with this...

    EDIT: I got it! x^2 +y^2 leq R^2 effectively cuts off the paraboloid at the x-y plane. The cross-section of the paraboloid on the x-y plane is the circle x^2+y^2 = R^2. Therefore the impact paramater cannnot be greater than R, which implies that [itex]\tan(\theta/2) \geq R/2a[/itex] as desired.
    Last edited: Jan 1, 2008
  2. jcsd
  3. Jan 1, 2008 #2
    The last part of this problem asks: Does the [itex]\sin^{-4}(\theta/4)[/itex] dependence have anything to do with Rutherford scattering?

    Anyone have any ideas?
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