A radioactive element `t_(0.5) = 30` days is spread over a room, Its activity is 25 times the permissible value of safe working. Calculate the number of days after which the room will be available for safe working.

Options

A. 139.37 days
B. 193.37 days
C. 183.37 days
D. 125.37 days

Answer

A

Explanation

Let r is activity for safe working ` therefore r_(0) = 25 r`
`lambda = (0.693)/(30) = 2.31 xx 10^(-2) "days"^(-1)` and `t = (2.303)/(2.31 xx 10^(-2)) log ""(25r)/(r) = 139.79` days