Pearson Edexcel · GCSE · Physics
Course version: 1PH0 · Version from Sept 2016
Describe the process of β– decay (a neutron becomes a proton plus an…
Full specification wording
Topic 6 – Radioactivity: 6.18 Describe the process of β– decay (a neutron becomes a proton plus an electron)
Beta-minus decay happens in an unstable nucleus that has too many neutrons.
Checked against the Pearson Edexcel 1PH0 specification (opens in a new tab) on .
- Point 17 of 42
Study notes
From the checked teaching notes for this specification point.
The idea
Beta-minus decay happens in an unstable nucleus that has too many neutrons. Inside the nucleus, one neutron changes into a proton and, in the process, an electron is created and ejected at high speed as a beta particle. The proton stays in the nucleus, so the atomic number increases by one while the mass number stays the same, because a proton replaces a neutron and the total number of nucleons is unchanged. The emitted electron carries away the energy and leaves the nucleus. For example, carbon-14 decays to nitrogen-14: the neutron count falls by one, the proton count rises by one, and a beta particle is released. The nuclear equation balances because the mass numbers match and the charge is conserved, with the proton's positive charge balanced by the electron's negative charge.
What earns the marks
- States that in beta-minus decay a neutron in the nucleus changes into a proton.
- States that an electron is created and emitted from the nucleus as the beta particle.
- Explains that the atomic number increases by one while the mass number stays the same.
- Identifies that the proton remains in the nucleus and the electron is ejected.
- Applies the change to an example such as carbon-14 becoming nitrogen-14 with a beta particle released.
Common mistakes and how to put them right
States that a proton turns into a neutron.
Put it right by stating that a neutron becomes a proton plus an electron.
Claims that the mass number decreases by one.
Put it right by noting that the mass number is unchanged because a proton replaces a neutron.
Says the beta particle is an electron that was already orbiting the nucleus.
Put it right by stating that the electron is created in the nucleus during the decay.
Exam tips
- Check that the mass number stays the same and the atomic number rises by one in the nuclear equation.
- Remember the beta particle is an electron emitted from the nucleus, not an orbiting electron.
- Use a named example such as carbon-14 to nitrogen-14 to show the change clearly.
Try the lesson
The start of the Topic 6 – Radioactivity: 6.18 Describe the process of β– decay (a neutron becomes a proton plus an electron) lesson, made from checked teaching notes for this specification point.
Have a go first
In beta-minus decay, what happens to a neutron inside the nucleus?
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