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Homework Help: Radioactive decay: How can you tell which is the daughter & parent?

  1. Feb 8, 2009 #1
    1. The problem statement, all variables and given/known data
    Analysis of the material shows that it contains both Gallium-64 (atomic mass = 63.936838u) and Zinc-64 (atomic mass = 63.929147u). Which nuclide is the parent nuclide and which is the daughter nuclide?

    2. Relevant equations

    3. The attempt at a solution
    The answer is supposed to be Ga-64.
    How can we tell it is Ga-64 if we are not given if it is beta plus or beta minus?

    Is it because we are supposed to assume that the decay will spontaneously happen? So that it will release the energy and go from a higher mass to a lower mass?

    But we dont know if someone bombarded energy to it or not...

    I was just wondering how you would look at this kind of problem.

    Thanks for your help.
  2. jcsd
  3. Feb 8, 2009 #2


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    All reactions are reversible. So sure if you bombard it with energy, yes, you can convert Zi-64 to Ga-64. But what's wrong with you original opinion that the high mass nucleus is the parent of the lower mass nucleus? Regardless of the decay mechanism. Beside if Ga->Zi you know it must be beta+, right?
  4. Feb 8, 2009 #3
    My question is.. So how do we know that Ga is the parent, if we are not informed of the fact that the reaction is not beta minus or plus?
  5. Feb 8, 2009 #4


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    You are just having a philosophical quibble, right? In nature, radioactive decay products are usually lost to the environment and there is no way to go back uphill energywise unless you put them into a particle accelerator or supernova. I think that's what the question is asking.
  6. Feb 8, 2009 #5
    I see. Thank you very much.
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