A freshly prepared radioactive source of half-life `2 h` emits radiation of intensity which is 64 times the permissible safe level. The minimum time after which it would be possible to work safely with this source is

Options

A. 128 h
B. 24 h
C. 6h
D. 12h

Answer

D

Explanation

After n number of half-life, `N=N_(0)((1)/(2))^(n)`
`1=64((1)/(2))^(n)implies((1)/(2))^(6)=((1)/(2))^(n)`
n = 6 i.e., half-lives
`therefore"Minimum time,"t=6xx2=12h`