Modern Physics 3 Question 15

15. Two radioactive materials X1 and X2 have decay constants 10λ and λ respectively. If initially they have the same number of nuclei, then the ratio of the number of nuclei of X1 to that of X2 will be 1/e after a time

(a) 1/10λ

(b) 1/11λ

(c) 11/10λ

(d) 1/9λ

(2000,2M)

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Solution:

  1. Nx1(t)Nx2(t)=1e or N0e10λtN0eλt=1e

(Initially, both have same number of nuclei say N0 )

 or e=eλt/e10λt or e=e9λt or 9λt=1 or t=19λ



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