Question

A freshly prepared radioactive source of half-life $2$$h$ emits radiation of intensity which is $64$ times the permissible save 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

Answer: (B)

$12$ $h$

The number of half lives required to decay to permissible decay is $n=lo{g}_{2}64=6$

Total time, $T=6\times 2h=12h$