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Elastic collision between an unknown mass and an alpha particle

  1. Jan 21, 2009 #1
    1. The problem statement, all variables and given/known data

    In an elastic collision between an alpha particle and an unknown nucleus at rest, the alpha particle was deflected through a right angle and lost 40 percent of its energy . Identify the mysterious nucleus.

    2. Relevant equations



    gamma is the ratio between the alpha mass particle and the unknown mass
    3. The attempt at a solution

    Is the deflected angle the recoil angle? If so then I can use the recoil angle to find phi. Then I can use phi to find gamma and with gamma since I know the mass of an alpha particle, I can find the unknown mass. When the problem says the recoil angle loses 40 % of its energy , doesn't that mean E2=.4E0
  2. jcsd
  3. Jan 22, 2009 #2


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    Hi pentazoid! :smile:

    Yes, the deflected angle is the recoil angle …

    but no, E2=.6E0 :wink:
  4. Jan 22, 2009 #3
    if my deflected angle is 90 degrees that means my phi is zero. which means sin(phi/2) is zero, which means then that there is no way to determine what the unknown mass is
  5. Jan 23, 2009 #4


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    I'm confused :confused:

    isn't φ = π/2?
  6. Jan 24, 2009 #5


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    Not if you mean the angle that the nucleas recoils. Conservation of energy and momentum determine this recoil angle.
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