Modern Physics 3 Question 18

18. The half-life of 131I is 8 days. Given a sample of 131I at time t=0, we can assert that

(1998,2M)

(a) no nucleus will decay before t=4 days

(b) no nucleus will decay before t=8 days

(c) all nuclei will decay before t=16 days

(d) a given nucleus may decay at any time after t=0

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Solution:

  1. Number of nuclei decreases exponentially

N=N0eλt and rate of decay dNdt=λN

Therefore, decay process lasts upto t=. Therefore, a given nucleus may decay at any time after t=0.



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