Question

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
(a) 6 h
(b) 12 h
(c) 24 h
(d) 128 h.

Answer 1

Explanation:

• To work safely with this source, the minimum time that is required is 12 hours.
• A newly produced radioactive source discharges radioactivity of power 64 times more than the permissible level.
• This shows that it is likely to safely work till the radioactive source’s six half-lives (as 26 = 64).
• Since the source’s half-life is 2 hours, the least time after which it would be likely to safely work with this source is 12 hours.

Answer 2

Answer:

12h

Explanation:

λ=$\frac{.693}{t_{1/2} }$

=2/.693

r=$r_{0}$$e^{-λt}$

1/64=$e^{-λt}$ (rearrange)

t=ln(64)*2/.693=12h