As accident in a nuclear laboratory resulting in deposition of a certain amount of radioactive material of half life `18 `days inside the laboratory Tests revealed that the radiation was `64` times more than the permissible level required for save operation of the laboratory what is the minimum number of days after which the laboratory can be considered safe for use?

Options

A. `64`
B. `90`
C. `108`
D. `120`

Answer

C

Explanation

Here, `T=18 days, t=? A/(A_(0))=64`
form `N/(N_(0))=A/(A_(0))=(1/2)^(n)`
`1/64=(1/2)^(n) :. n=6`
As `n=t/T, t=nT=6xx18=108days`