Question

A freshly prepared radioactive source of half life period 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 with this source is:

• A. 6 hours
• B. 12 hours
• C. 24 hours
• D. 48 hours

Answer 1

Answer: (B)

12 hours

The half-life period is 2 hours.

The decay constant $\lambda =\frac{0.693}{t_{1/2}}=\frac{0.693}{2}=0.3465h{r}^{-1}$

The radiations have an intensity which is 64 times the permissible safe level.

$\frac{N_0}{N_t}=64$

The minimum time after which it would be possible to work with this source is

$t=\frac{2.303}{\lambda }log\frac{N_0}{N_t}=\frac{2.303}{0.3465}log64=12hr$