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Homework Help: Half-Life physics problem

  1. May 12, 2004 #1
    Radon-222 is a radioactive gas with a half-life of 3.82 days. A gas sample contains 4.5*10^8 radon atoms initially.
    Estimate how many radon atoms will remain after 12 days.
    This Is what i have done:
    3.82 days=3.82*24*60*60=330048seconds
    what's next?
  2. jcsd
  3. May 12, 2004 #2

    Doc Al

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    Staff: Mentor

    12 days is how many half-lives? What does half-life mean? How much is left after one half-life? Two half-lives?
  4. May 12, 2004 #3


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    You don't need seconds. After one half-life, you're dividing by 2. If you determine how many half-lifes are in 12 days, you'll know how many times to divide by 2.

    As an example, if you divided by 2 twice, you would have:

    [tex]\frac{4.5 \ast 10^8}{2 \ast 2}[/tex]


    [tex]\frac{4.5 \ast 10^8}{2^2}[/tex]

    If dividing by 2 three times:

    [tex]\frac{4.5 \ast 10^8}{2 \ast 2 \ast 2}[/tex]


    [tex]\frac{4.5 \ast 10^8}{2^3}[/tex]

    The power in the denominator is however many times you want to divide by 2 and doesn't have to be an integer.
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