Question

A solution containing active cobalt 6027Co having activity of 0.8μCi and decay constant λ is injected in an animal's body. If 1cm3 of blood is drawn from the animal's body after 10 hrs of injection, the activity found was 300 decays per minute. What is the volume of blood that is flowing in the body? (1Ci=3.7×1010 decay per second and at t=10hrs eλt=0.84)

A
6 litres
B
7 litres
C
4 litres
D
5 litres
Solution
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The activity equation can be written as
dNdt=λNoeλt
given that
λNo=0.8μCi
Putting the values,
λNo=2.96×104
Let the volume of the blood flowing be V,
the activity would reduce by a factor of 103V
Hence
λNo103Veλt=300/60 (Both R.H.S. and L.H.S. are decay/s)
Putting the values of eλt and λNo we get
V=5litre

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