Pearson Edexcel · GCSE · Physics
Course version: 1PH0 · Version from Sept 2016
Describe the process of β+ decay (a proton becomes a neutron plus a…
Full specification wording
Topic 6 – Radioactivity: 6.19 Describe the process of β+ decay (a proton becomes a neutron plus a positron)
Beta-plus (β⁺) decay is a nuclear change in which a proton inside an unstable nucleus turns into a neutron and a positron is emitted.
Checked against the Pearson Edexcel 1PH0 specification (opens in a new tab) on .
- Point 18 of 42
Study notes
From the checked teaching notes for this specification point.
The idea
Beta-plus (β⁺) decay is a nuclear change in which a proton inside an unstable nucleus turns into a neutron and a positron is emitted. The nucleus therefore loses one unit of positive charge: the proton count falls by one, so the atomic (proton) number decreases by 1, while the total number of nucleons stays the same, so the mass (nucleon) number is unchanged. The positron is the antiparticle of the electron: it has the same mass as an electron but a charge of 1⁺. A convenient way to track the change is to write the nuclear equation and check that both the mass numbers and the charge totals balance on each side. Beta-plus decay is a proton-to-neutron conversion, so it is distinct from beta-minus decay, in which a neutron becomes a proton and an electron is emitted.
What earns the marks
- States that a proton in the nucleus changes into a neutron and a positron is emitted.
- Identifies the positron as having the mass of an electron and a charge of 1⁺.
- Explains that the atomic (proton) number decreases by 1 because one proton is lost.
- Explains that the mass (nucleon) number stays the same because the total number of nucleons is unchanged.
- Balances a nuclear equation for β⁺ decay by checking mass numbers and charge totals on each side.
Common mistakes and how to put them right
Confuses β⁺ decay with β⁻ decay.
Put it right: β⁺ decay converts a proton into a neutron and emits a positron.
Claims the mass number falls by one.
Put it right: Keep the mass number unchanged because a proton is replaced by a neutron.
Describes the positron as a proton or as a positive ion.
Put it right: State that it is the antiparticle of the electron with charge 1⁺.
Exam tips
- Write the nuclear equation first, then check that mass numbers and charge totals balance on both sides.
- Use the phrase 'proton becomes a neutron plus a positron' to keep the direction of change clear.
- Distinguish β⁺ from β⁻ by naming the particle emitted and the nucleon that changes.
Try the lesson
The start of the Topic 6 – Radioactivity: 6.19 Describe the process of β+ decay (a proton becomes a neutron plus a positron) lesson, made from checked teaching notes for this specification point.
Have a go first
In beta-plus decay, what happens to a proton inside the nucleus?
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