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Homework Help: Differential cross-section and scattering.

  1. Apr 13, 2010 #1
    1. The problem statement, all variables and given/known data

    A beam of 0.38 MeV neutrons is incident on a 113Cd foil of thickness 1mm. The absorption
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    cross-section for 0.38 MeV neutrons is 5 barns. What is the fraction of neutrons absorbed by the foil?


    3. The attempt at a solution

    I'm not sure whether I should treat this as scattering in a thick or thin foil and how the energy of the incoming particles is related to the total scattering of particles.


    Thanks.
     
  2. jcsd
  3. Apr 14, 2010 #2
  4. Apr 14, 2010 #3
    Hi! I tried using the formulae given in that webpage. Problem is I dont know where the kinetic energy of the neutron (0.38 MeV) comes in into that equation. Anyhow I still get the wrong answer..
     
  5. Apr 15, 2010 #4
    Just post your calculation. People will help you.
     
  6. Apr 17, 2010 #5
    For scattering in a thin foil:

    R = F σ n A dx

    We have to find R/F and then to get fraction of neutrons absorbed by foil (1 - R/F)

    We know what σ, n and dx are, but not A. I dont know why they give me the energy value of the neutrons...?
     
  7. Apr 17, 2010 #6
    Please write what is n, A , etc..because many people use their own convention so better to write the key. Is A the mass number of target. ?
    Did you miss anything in your question?
    Okay i just made a simple calculation using the formula found in that website..
    is your solution, i.e the fraction of neutron beam scattered is 0.023? (1-0.23)=0.977.
    In fact i am sorry i also don't know why they have given the energy of beam.
     
  8. Apr 19, 2010 #7
    Sorry forgot about that.

    F = flux incident on target. (particles per m² per sec)

    A = Total area of foil

    n = number density of target atoms
    σ = scattering cross section
    dx = thickness of foil

    Im having the exact same problem, I still cant figure it out.


    Thanks.
     
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