Two radioactive substances A and B have decay constants 5 and respectively. At t = 0 they have the same number of nuclei. The ratio of number of nuclei of A to those of B will be ( 1e )2 after a time interval
(3) 12
By the law of radioactive decay, N = N0 e- t, so NA = N0 e-5 t and NB = N0 e- t, which gives
NANB = e-4 t
This is given to be ( 1e )2 = e-2, so
4 t = 2
∴ t = 12
Answer: (3)
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