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Proving the half-life of Potassium-40

  1. Mar 18, 2013 #1
    1. The problem statement, all variables and given/known data

    "K-40... decays by two radioactive processes. It can decay by electron capture or β- emission.

    It is found that a sample containing 4.0x10^18 nuclei of K-40 emits a total of 68 β- particles and photons each second. This shows the half life is 1.3x10^9 years."

    Use the data in the passage to show that the half life is 1.3x10^9 years.

    2. Relevant equations

    I'm assuming...

    T1/2 = ln2/λ; A=λN; A=A0e^(-λ)(t)

    3. The attempt at a solution

    Using A=λN --> A/N=λ --> (68)/(4*10^18) = 1.7^10-17
    then ln2/(1.7^10-17) = 4.1*10^16 ->> waayy too big.

    I then tried various other combinations of the above, but to no success.

    Please help!! I know I'm missing something VERY obvious.
     
  2. jcsd
  3. Mar 18, 2013 #2

    phyzguy

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    Science Advisor

    You calculated (correctly) the half-life in seconds. Now convert to years.
     
  4. Mar 18, 2013 #3
    D'oh!!!!!!!!!!!!

    You legend, thank you :D
     
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