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Homework Help: Half-Time decay

  1. Nov 30, 2011 #1
    1. The problem statement, all variables and given/known data
    When iodine is ingested by humans they eliminate it such that on half of the body's iodine content is execreted every 4.0 days. Radioactive 131I with a physical half-life of 8.1 days is administered to a patient. When will only 1% of the isotope remain in the patient's body?

    2. Relevant equations
    1/T1/2, e = 1/T1/2,p + 1/T1/2,b

    3. The attempt at a solution
    I got the rest of the equation but I dont know how people got T1/2,e = 2.7 d

    Help please!
  2. jcsd
  3. Nov 30, 2011 #2


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    Homework Helper

    It looks like simple arithmetic??

    1/T1/2, e = 1/T1/2,p + 1/T1/2,b

    1/T1/2, e = 1/4 + 1/8.1

    1/T1/2, e = 0.37345679

    T1/2, e = 2.67768595 better known as 2.7d
  4. Nov 30, 2011 #3
    Ah I was thinking so much, I overlooked it. Thank you though!
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