Question

10 gm of radioactive material of half-life 15 year is kept in store for 20 years. The disintegrated material is.

• A. 12.5 g
• B. 10.5 g
• C. 6.03 g
• D. 4.03 g

Answer 1

Answer: (C)

6.03 g

Answer 2

Remaining material $N = \frac{N_{0}}{2^{t/T}}$

$\Rightarrow N = \frac{10}{(2)^{20/15}} = \frac{10}{2.15} = 3.96\mspace{6mu} gm$

So decayed material

$= 10 - 3.96 = 6.04\mspace{6mu} gm$