Nuclear Physics and RadioactivityHard
Question
The half life of a radioactive substance is 20 minutes. The approximate time interval (t2 - t1) between the time t2 when 
of it has decayed and time t1 and 
of it had decayed is :
of it has decayed and time t1 and of it had decayed is :Options
A.14 min
B.20 min
C.28 min
D.7 min
Solution
t1/2 = 20 minutes
N = N0e-λt2 λt1 ln 3
N0 = N0e-λt2 t1 = 
ln 3
N0 = N0e-λt2 t2 = ln 3
t2 - t1 =
= t2 - t1 =
= 20 min
N = N0e-λt2 λt1 ln 3
N0 = N0e-λt2 t1 = ln 3N0 = N0e-λt2 t2 = ln 3t2 - t1 =
= t2 - t1 =
= 20 min
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