Question

Activity of a radioactive element decreased to one third of original activity $I_0$ in 9 years. After further 9 years. Its activity will be

• A. $I_0$
• B. $\frac{2}{3}{I}_0$
• C. $\frac{I_0}{9}$
• D. $\frac{I_0}{6}$

Answer 1

The correct option is C

$\frac{I_0}{9}$

$I=\frac{I_0}{2^n},\frac{I_0}{3}=\frac{I_0}{2^{\frac{9}{T}}}$

$I^{{}^{\prime }}=\frac{I_0}{2^{\frac{18}{T}}}=\frac{I_0}{(2^{\frac{9}{T}}{)}^2}=\frac{I_0}{9}$