question_answer

Plutonium decays with a half-life of 24,000 years. If plutonium is stored for 72,000 years, what fraction of its remains?   

Answer:

                No. of half-lives \[\text{=}\frac{\text{Time of disintegration}}{\text{Half-life period}}=\frac{72,000}{24,000}=3\] \[\therefore \]  \[\frac{N}{{{N}_{0}}}={{\left( \frac{1}{2} \right)}^{3}}=\frac{\mathbf{1}}{\mathbf{8}}\]