Find the half-life period of a radioactive material if its activity drops of `(1/16)^(th)` of its initial value in 40 years.

Explanation

`R/(R_0)=(1/2)^n`
`1/(16)=(1/2)^n`
`rArr (1/2)^4=(1/2)^n`
`rArr n=4`
`T_(1//2)=t/n=(40)/4=10` years.