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Chemistry - radioactivity

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Hello Dr.Bob. Could you check my work please? I'm not sure if I'm right in how I solved this problem.

Which of the following nuclides are most likely to decay via beta decay?

A) I-131 B) Pb-206 C) F-18 D) Zr-90 E) Ar-40

I know that nuclides undergo beta decay when they are too heavy to be stable. Out of the nuclides listed, three can be considered heavy. These are: Pb-206 which has atomic mass of 207.2, F-18 with atomic mass of 19 and Zr-90 with atomic mass of 91.22. Would it be enough for a question like this to reason that since the difference between the atomic numbers is the greatest for Zr-90, then it is the nuclide which is more likely to decay? Or do I need to take the valley of stability into consideration? The reason I ask about the valley of stability is because a question like this will likely be on the exam and I don't believe we need to memorize the table of stability.


Thank you so much for your help.

  • Chemistry - radioactivity - ,

    I don't know how to answer your question. I believe I-131 is the only element listed that decays by beta emission (F-18 decays by positron emission). How did I know that. It has little to do with theory. I know I-131 is a radioactive isotope and decays by beta emission. I looked all of the others up on Google and found they are stable except for F-18 with is a positron emitter. That doesn't address the question of how you can tell. Note, for example, that I-131 has a N:P ratio of 1.47 and decays by beta emission while Pb-206 has N:P ratio of 1.51 and is stable. And C-14 has N:P ratio of 1.22 and decays. Perhaps another tutor can help.

  • Chemistry - radioactivity - ,

    Hello Dr.Bob, could you please help me with this problem:
    Which of the following nuclides are most likely to decay via beta decay?
    a)200 78 Pt b)192 78 Pt c)188 78 Pt
    d)196 78 Pt

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