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Old Aug 30th 2010, 11:26 PM   #1
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Activity of sample after time

A small volume of a solution which contained a radioactive isotope of sodium had an activity of 12000 disintegrations per minute when it was injected into the bloodstream of a patient. After 39 hours the activity of 1.0cm^3 of blood was 0.50 disintegrations per minute. If the half-life of the sodium isotope is taken as 15 hours, estimate the volume of blood in the patient.

I calculated (lambda)=ln2/(15*60*60)=1.28*10^(-5)
Original number of atoms=(12000/60)/1.28*10^(-5)=15581106
number after 39h=15581106*e^(-1.28*10^(-5)*39*60*60)=2569924
activity=1.28*10^(-5)*2569924=33.0 /s=1979.3 /min
Volume=1979.3/0.5=3958.5 cm^3

Answer is 6000.
Thanks!
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Old Aug 31st 2010, 12:11 AM   #2
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I am getting the same answer which you have got.
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