Question

A freshly prepared radiocative 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 -

(A) 6 h 

(B) 12 h

(C) 24 h 

(D) 128 h

Answer 1

Correct Answer is: (B) 12 h

64 = 2⁶

After 6 half lives activity will become = 1/64

Hence required time = 6 × 2h = 12h .