physics

How long will it take a sample of polonium-210 with a half-life of 140 days to decay to one-sixty-fourth of its original strength?

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asked by katie
  1. 1/2 = e^k(140)
    ln .5 = 140 k
    k = .00495
    so
    1/64 = e^-.00495 t

    -4.159 = -.00495 t
    t = 840 days

    posted by Damon
  2. alternatively
    1/64 = (1/2)^6
    so 6 half lives
    =140*6 = 840 days

    posted by Damon

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