Question

A freshly prepared radioactive source of half-life 2 hours emits radiations 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 hours
• B. 12 hours
• C. 24 hours
• D. 128 hours

Answer 1

The correct option is B 12 hours

$N=\frac{N_0}{64}=\frac{N_0}{2^6}\therefore n=6$
Thus total time $=2\times 6=12hr$.