NEET | 2017Nuclear Physics and RadioactivityHard

Question

Radioactive material 'A' has decay constant '8 λ' and material 'B' has decay constant 'λ'. Initially they have same number of nuclei. After what time, the ratio of number of nuclei of material 'B' to that 'A' will be 1/e ?

Options

A.

17λ

B.

18λ

C.

19λ

D.

1λ

Solution

λA=8 λ, λB=λ
⇒ NB=NAe⇒ N0 e-λt-N0 e-8λte
⇒ -λt =- 8λt-1 ⇒7λt=-1⇒t=-17λ
Best answer is t = 17λ

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