The initial number of radioactive atoms in a radioactive sample is `N_0`. If after time t the number of becomes N, then `N=N_0e^(-lambdat)`, where `lambda` is known as the decay constant of the element. The time in which the number of radioactive atoms becomes half of its initial number is called the half-life (T) of the element. The time in which the number of atoms falls to 1/e times of its initial number is the mean life `(tau)` of the element. The product `lambdaN` is the activity (A) of the radioactive sample when the number of atoms is N. The SI unit of activity is bequerel (Bq)' where 1 Bq = 1 decay.`s^(-1)`.

The half-life of Iodine-131 is 8 d. Its mean life (in SI) is -

(A) `4.79xx10^5` s.
(B) `6.912xx10^5` s.
(C) `9.974 xx 10^5` s.
(D) `22.96xx10^5` s.

Options

A. `4.79xx10^5`
B. `6.912xx10^5`
C. `9.974 xx 10^5`
D. `22.96xx10^5`

Answer

c