Modern Physics 3 Question 28

29. A freshly prepared sample of a radioisotope of half-life 1386s has activity 103 disintegrations per second. Given that ln2=0.693, the fraction of the initial number of nuclei (expressed in nearest integer percentage) that will decay in the first 80s after preparation of the sample is

(2013 Adv.)

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Solution:

  1. Number of nuclei decayed in time t,

Nd=N0(1eλt)=(1eλtd)×100

Here, λ=0.6931386=5×104s1

decayed (λt)×100

=(5×104)(80)(100)=4



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