Atoms And Nuclei Question 409

Question: A radioactive element decays by p emission. A detector records n beta particles in 2 second and in next 2 seconds it records 0.75n beta particles. Find mean life corrected to nearest whole number. Given n2=0.6931 and n3=1.0986. .

Options:

A) 6.9sec

B) 9.9sec

C) 10.1sec

D) 12.2sec

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Answer:

Correct Answer: A

Solution:

  • We know that, N=N0eλt

After 2 second, N1=N0eλ×2 After (2+2) second, N2=N0eλ×4 According to given conditions, N0N1=n or N0N0e2λ=n …(i) and

N0e2λN0e4λ=0.75,n … (ii)

After solving above equations, we get λ=0.145,s Mean life T=1/λ=6.9s .



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