Question

The half life of $131I$is 8 days. Given a sample of $131I$at time t = 0, we can assert that .

• A. No nucleus will decay before t = 4 days
• B. No nucleus will decay before t = 8 days
• C. All nuclei will decay before t = 16 days
• D. A given nucleus may decay at any time after t = 0

Answer 1

Answer: (D)

A given nucleus may decay at any time after t = 0

Answer 2

Number of nuclei decreases exponentially

$N = N_{0}e^{- \lambda t}$ and Rate of decay $\left( - \frac{dN}{dt} \right) = \lambda N$

Therefore, decay process losts up to t = ∞.

Therefore, a given nucleus may decay at any time after t = 0.