Question

The half life of polonium is 140 days. After how many days, 16 gm polonium will be reduced to 1 gm (or 15g will decay).

• A. 700 days
• B. 280 days
• C. 560 days
• D. 420 days

Answer 1

Answer: (C)

560 days

Answer 2

$\frac{N}{N_{0}} = \left( \frac{1}{2} \right)^{t/140} \Rightarrow \frac{1}{16} = \left( \frac{1}{2} \right)^{t/140}.$

$\Rightarrow \frac{t}{140} = 4 \Rightarrow t = 560\mspace{6mu} days$