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Two radioactive materials A and B 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 A to that of B will be 1/e after a time
- 1/10λ
- 1/11λ
- 1/9λ
- 1/11λ
Correct answer: 1/9λ
Solution
N_A/N_B = e^(-10*lambda*t)/e^(-lambda*t) = e^(-9*lambda*t). Setting this to 1/e gives 9*lambda*t = 1, so t = 1/(9*lambda).
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