Radioactive decay

Overview

The random nature of decay, the decay constant, the exponential decay law, activity and half-life.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   Why is it impossible to predict exactly when a specific radioactive nucleus will decay?

   Model answer

   Radioactive decay is a random process, so the exact moment of decay for any individual nucleus cannot be determined.

2. 2

   Does the probability of a radioactive nucleus decaying depend on how long it has already existed?

   Model answer

   No, each nucleus has a constant probability of decaying per unit time, regardless of how long it has existed.

3. 3

   Do external conditions such as temperature or pressure affect the probability of radioactive decay?

   Model answer

   No, the probability of decay per unit time remains constant regardless of external conditions.

4. 4

   What does the decay constant λ represent?

   Model answer

   The decay constant represents the probability of decay per unit time for a given nucleus.

5. 5

   What are the units of the decay constant λ?

   Model answer

   s⁻¹ (or per second, or inverse time units such as min⁻¹ or yr⁻¹).

6. 6

   State the equation that relates the rate of change of undecayed nuclei to the number of undecayed nuclei present.

   Model answer

   ΔN/Δt = −λN, where N is the number of undecayed nuclei and λ is the decay constant.

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