Beta-decay energy

  1. I have to work out which if these two beta-decay processes are energetically possible, given that the beta-decay energy of Li-11 is Q = 20 MeV. The two processes are:

    (1)
    〖Li〗_11→〖Be〗_9+2n
    (2)
    〖Li〗_11→〖He〗_3+〖He〗_8



    I am supposed to use the energy conditions for beta-decay equations, i.e.:

    Q={M(Z,A)-M(Z+1,A)-m_e } c^2
    Q={M(Z,A)-M(Z-1,A)-m_e } c^2

    But I don’t know which one; in the first process the numbers of neutrons and protons both decrease by one – how is this possible? (In the second process, the number of neutrons decreases by one and the number of protons increases by one, so I guess that is beta-minus).

    Basically, I don’t understand how the decay process works, and from then how to calculate Q when there are two daughter nuclei. So an explanation would be much appreciated.

    Thanks!
     
  2. jcsd
  3. mfb

    Staff: Mentor

    11=9+2, the total number of nucleons stays the same. As you get one new proton, the number of neutrons decreases by one.

    Just add both nuclei.

    This is energy conservation - the total available energy is given by the mass of ##{}^11Li##, and you have to check if that is sufficient to produce all daughter particles.
     
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