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. 6 hrs
B. 12 hrs
C. 24 hrs
D. 128 hrs

Answer

b

Explanation

`N = N_(0) ((1)/(2))^(n)`
`(N)/(N_(0)) = ((1)/(2))^(n)`
`(1)/(64) = ((1)/(2))^(n)`
`n = 6`
`:. T = 2 xx 6 = 12` hours