Question

The half-life of a $C{o}^{60}$ isotope is $5.2$ years. If $1.0g$ of cobalt $C{o}^{60}$ decays with time, the amount (in grams) remaining after $20.8$ years is

• A. $0.25$
• B. $0.50$
• C. $0.125$
• D. $0.0625$

Answer 1

The correct option is D $0.0625$

Half life of a cobalt 60 isotope $=5.2years$

After 4 half-lives, i.e., 20.8 years, the fraction of isotope left $=(\frac{1}{2}{)}^4=\frac{1}{16}$

So, amount of gms remaining $=\frac{1}{16}of1gms$

$=0.0625gms$