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Homework Help: Lithium Threshold Energy

  1. Jun 21, 2011 #1
    1. The problem statement, all variables and given/known data
    A thin target of lithium is bombarded by helium nuclei of energy E0. The lithium nuclei are initially at rest and are essentially unbound for this high-energy collision. A nuclear reaction can occur in which
    4He + 7Li → 10B + 1n −2.8 MeV
    The collision is inelastic, and the final kinetic energy is less than E0 by 2.8 MeV. (1 MeV = 106 eV = 1.6 ×10−13 J). The relative masses of the particles are: helium, mass 4; lithium, mass 7; boron, mass 10; neutron, mass 1.

    (a) Determine the threshold energy, i.e., the minimum value of E0 for which neutrons can be produced. [HINT: Analyze the collision in the center-of-mass frame of reference. At the threshold energy, the final particles are produced at rest in the center-of-mass frame.]


    (b) Calculate the energy of the neutron at the threshold energy.


    (c) Determine the threshold energy for the reaction
    4He + A(Iso1) → A+3(Iso2) + 1n − β
    where β is the inelastic energy loss.
    Data: A = 10; β = 3.1 MeV.


    2. Relevant equations

    Pi=Pf

    KE=.5mv^2-Q; Q is the energy lost in the collision

    3. The attempt at a solution

    I am not sure if this remotely correct, but this is my best attempt:

    m_he*Vo=(m_he+m_li)*Vo'
    Eo=.5(m_he+m_li)*Vo'^2-Q
     
  2. jcsd
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