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.