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If a radioactive isotope has half life of 5 days,how long will it take for its radioactive strength to be a maximum of one thousandth,(1/1000) of its original value?

  • Science -

    1/2 = e^-5k
    ln .5 = -5 k
    k = .1386

    so
    x = Xo e^-.1386 t

    .001 = e^-.1386 t

    -6.91 = -.1386 t
    t = 49.8 days

    check
    about 10 five day periods
    .5^10 = .000976
    close enough to .001

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