Nuclear instability

Overview

The N against Z plot, the stability line, and the decay each region undergoes.

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

   On a graph of neutron number (N) against proton number (Z), what is the relationship between N and Z for light stable nuclei?

   Model answer

   Light stable nuclei have approximately equal numbers of protons and neutrons (N ≈ Z).

2. 2

   How does the neutron-to-proton ratio change for heavier stable nuclei compared to lighter ones?

   Model answer

   Heavier stable nuclei require progressively more neutrons than protons for stability, so the N/Z ratio increases with increasing Z.

3. 3

   What does the line N = Z represent on a graph of neutron number against proton number?

   Model answer

   The line N = Z represents equal numbers of neutrons and protons in the nucleus.

4. 4

   Where does the stability band lie relative to the N = Z line, and how does this change with increasing proton number?

   Model answer

   Stable nuclei lie along or above the N = Z line, with the stability band curving increasingly above N = Z as Z increases.

5. 5

   Which type of nuclei typically undergo alpha decay?

   Model answer

   Heavy nuclei with more than 82 protons (Z > 82), lying above the top of the stability band. (Proton-rich nuclei instead undergo beta-plus decay or electron capture.)

6. 6

   What type of nuclear instability leads to beta-minus (β⁻) decay?

   Model answer

   Nuclei with an excess of neutrons relative to protons undergo β⁻ decay.

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