The half-life of a radioactive nucleus is 20 hours. What fraction of original activity will remain after 40 hours?

Explanation

40 h means 2 half - lives. Thus,
`A=(A_(0))/(2^(2)) =(A_(0))/(4)` or `(A)/(A_(0)) =(1)/(4)`
So, one - fourth of the original activity will remain after `40 h`.
Specific acticity: The activity per unit mass is called specific acticity.