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  1. The half life of a radioactive nucleus is 50 days. The time interval (t2 – t1 ) between the time t2 when 2/3 of it has decayed and the time t1 when 1/3 of it had decayed is :
    1. 30 days
    2. 50 days
    3. 60 days
    4. 15 days
Correct Option: B

N1 = N1 e–λt

N1 =
1
N0
3

N0
= N0e- λt2
3

1
= e- λt2 ....(i)
3

N2 =
2
N0
3

2
N0 = N0e- λt1
3

2
= e- λt1
3

Dividing equation (i) by equation (ii)
1
= e- λ(t2 - t1)
2

λ(t2 - t1) In 2
t2 - t1 =
In 2
= T1/2 = 50 days
λ



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