Question

Two radioactive substances A and B have decay constants $5\lambda$ and $\lambda$ respectively. At $t=0$, they have the same number of nuclei. The ratio of number of nuclei of A to that of B will be $(1/e{)}^2$ after a time interval of

• A. $\frac{1}{\lambda }$
• B. $\frac{1}{2\lambda }$
• C. $\frac{1}{3\lambda }$
• D. $\frac{1}{4\lambda }$

Answer 1

Answer: (B)

We know that: $N=N_0{e}^{-\lambda t}$
For A: $N_A=N_0{e}^{-5\lambda t}$
For B: $N_B=N_0{e}^{-\lambda t}$