A radioactive element `(t_(1//2) = 50 days)` is spread over a room. Its activity is `30` times the permisisble value for safe working. Calculate the number of days after which the room will be available for safe working.

Explanation

`r_(0) = 30r`
where `r` is the activity for safe working
`t = (2.303)/(k)log.(r_(0))/(r )(r_(0) prop N_(0) and r prop N)`
`t = (2.303)/(0.693) log.(30r)/(r )` , `(because k = (0.693)/(t_(1//2)))`
`= 245.44 days`