Question

Let T be the mean life of a radioactive sample. 75% of the active nuclei present in the sample initially will decay in time-

• A. 2 T
• B. (ln 2) $\frac{T}{2}$
• C. 4 T
• D. 2(ln 2) T

Answer 1

Answer: (D)

2(ln 2) T

Answer 2

When 75% decays, 25% is left undecayed. This required a time t = 2T_1/2, where T_1/2 =$\frac { \ln 2 } { \lambda }$and also, l =

\ t = $2 \left( \frac { \ln 2 } { \lambda } \right)$ = 2(ln 2)T