Question

The half life period is 5 years. After how much activity reduced to 3.125%

Answer 1

100----->50----->25----->12.5----->6.25----->3.125.

now...it's half life period is 5 years..it means it become half after every 5 year.

so...it takes 5 half life's to remain 3.125 %...

so...5×5 =25 years.

it remains 3.125% after 25 years.