AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
So beta decay does not cause the mass of the nucleus to change but does…
Full specification wording
Nuclear equations: So beta decay does not cause the mass of the nucleus to change but does cause the charge of the nucleus to increase.
In beta decay a neutron inside the nucleus turns into a proton, and the electron created in the process is ejected as the beta particle.
Checked against the AQA 8463 specification (opens in a new tab) on .
- Point 3 of 6
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
In beta decay a neutron inside the nucleus turns into a proton, and the electron created in the process is ejected as the beta particle. Count the nucleons: one neutron has gone but one proton has appeared, so the total is unchanged and the mass number stays the same. Count the charge: there is now one more proton, so the atomic number rises by one and the daughter is the next element along in the periodic table. For example ¹⁴₆C → ¹⁴₇N + ⁰₋₁e, where 14 = 14 + 0 and 7 + (-1) = 6. A rise of one in the proton number with no change in mass number is the signature that identifies a decay as beta.
What earns the marks
- Stating that the mass number is unchanged in beta decay.
- Stating that the atomic number increases by one.
- Explaining that a neutron in the nucleus changes into a proton.
- Identifying a decay as beta because the proton number has gone up by one.
Common mistakes and how to put them right
Reducing the mass number by one because an electron has been emitted.
Decreasing the atomic number instead of increasing it.
Saying the emitted electron came from an electron shell outside the nucleus.
Claiming the number of neutrons in the nucleus is unchanged.
Exam tips
- Remember the mass number is unchanged because a neutron is replaced by a proton, both of relative mass 1.
- Use the -1 on the beta particle when you check the atomic number column; it must be included in the total.
- If a question asks which radiation was emitted, compare the two atomic numbers first.
Try the lesson
The start of the Nuclear equations: So beta decay does not cause the mass of the nucleus to change but does cause the charge of the nucleus to increase. lesson, made from checked teaching notes for this specification point.
Have a go first
A nucleus of carbon-14 undergoes beta decay. What happens to the mass number and the charge of the nucleus?
Listen
In beta decay a neutron inside the nucleus turns into a proton, and the electron created in the process is ejected as the beta particle. Count the nucleons: one neutron has gone but one proton has appeared, so the total is unchanged and the mass number stays the same. Count the charge: there is now one more proton, so the atomic number rises by one and the daughter is the next element along in the periodic table. For example ¹⁴₆C → ¹⁴₇N + ⁰₋₁e, where 14 = 14 + 0 and 7 + (-1) = 6. A rise of one in the proton number with no change in mass number is the signature that identifies a decay as beta. A strong answer earns marks for these points. stating that the mass number is unchanged in beta decay. stating that the atomic number increases by one. explaining that a neutron in the nucleus changes into a proton. identifying a decay as beta because the proton number has gone up by one. Exam tip: Remember the mass number is unchanged because a neutron is replaced by a proton, both of relative mass 1.
Key words
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beta decay
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unchanged mass number
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increased atomic number
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identifying decay type
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See every definition
- beta decay
- A neutron inside the nucleus turns into a proton, and the electron created in the process is ejected as the beta particle.
- unchanged mass number
- One neutron has gone but one proton has appeared, so the total is unchanged and the mass number stays the same.
- increased atomic number
- There is now one more proton, so the atomic number rises by one and the daughter is the next element along in the periodic table.
- identifying decay type
- A rise of one in the proton number with no change in mass number is the signature that identifies a decay as beta.
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