Question

The activity of a radioactive element decreases to one-third of the original activity I₀ in a period of nine years. After a further lapse of nine years its activity will be –

• A. I₀
• B. (2/3)I₀
• C. (I₀/9)
• D. (I₀/6)

Answer 1

Answer: (C)

(I₀/9)

Answer 2

I =I₀ e^–lt ; $\frac { \mathrm { I } _ { 0 } } { 3 }$ = I₀ e^–9l Ž e^–9l = 1/3

I = I₀ e^–l×18 Ž I = I₀ (e^{–l × 9})² ; I = I₀ (1/3)² = $\frac { \mathrm { I } _ { 0 } } { 9 }$