physics-Radioactivity

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1) The number of radioactive nuclei in a particular sample decreases over a period of 15 days to one-seventeenth the original number. What is the half-life (in days) of these nuclei?
2) What is the activity of a sample of 14C that contains 1.22E+21 nuclei?

  • physics-Radioactivity -

    1) n(t) = No e^-kt
    where n is number at t and No is starting number
    when t = 15. n/No = 1/17 = .0588
    so
    .0588 = e^-15k
    ln .0588 = -15 k
    k = -2.833/-15 = .18888
    so
    what is t when n/No = 1/2 ??
    .5 = e^-.18888 t
    ln .5 = -.693 = -.18888 t
    t = 3.67 days half life

  • physics-Radioactivity -

    Thanks a lot Damon
    Is my answer for the second problem correct?

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