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 hours
B. 12 hours
C. 24 hours
D. 128 hours

Answer

B

Explanation

(b) `(N)/(N_0) = ((1)/(2))^n rArr (1)/(64) = ((1)/(2))^6`
=`((1)/(2))^n rArr n = 6`
after `6` half lives intensity emitted will be safe.
`:.` Total time taken `= 6 xx 2 = 12 hrs`.