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Homework Help: Can someone please check this radiochemistry question please

  1. May 17, 2009 #1
    1. The problem statement, all variables and given/known data

    A sample of sodium pertechnetate injection was found to have an activity of 51439 counts per minute (cpm). The sample was measured again exactly after 8 hours and found to have an activity of 20476 cpm. Calculate the half life of sodium pertechnatate.

    2. Relevant equations

    A = A0 e^-lamdat
    ln A = in A0 - lamdat
    half life = ln2/lamda

    3. The attempt at a solution

    ln 20476 = ln 51439 -lamda * 8
    9.927008748 = 10.84815192 - lamda * 8
    0.9150875487/8 = -lamda
    lamda = 0.1143859436

    half life = 6.06 hours

    Is this correct? I think I did the algebra a bit wrong but the answer of 6 hours sounds about right... can anyone help please...thanks.
  2. jcsd
  3. May 17, 2009 #2
    Okay I went wrong... I now get the answer of 6.02 hours...
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