7.2.2Nuclear Physics
Alpha, Beta and Gamma Radiation — Oxford AQA International GCSE Combined Science - Physics Revision Notes & Topical Questions
5 min read 7 parts Lesson 7 of 12
Section 1 of 7Radioactive decay
Unstable nuclei
- Unstable nuclei Some nuclei are unstable.
- They become more stable by emitting radiation, and substances that do this are called radioactive.
Random and spontaneous
- Random and spontaneous Decay happens without any outside trigger.
- It is impossible to know which nucleus will decay next or when;
- only the probability of decay in a given time can be estimated.
- It is impossible to know which nucleus will decay next or when;
Not affected by conditions
- Not affected by conditions The rate of decay is not changed by temperature, pressure or chemical reactions.
Section 2 of 7The types of radiation
| Radiation | What it is | Relative charge | Relative mass |
|---|---|---|---|
| Alpha (α) | A helium nucleus: 2 protons and 2 neutrons | +2 | 4 |
| Beta (β−) | A high-speed electron from the nucleus | −1 | very small |
| Gamma (γ) | Electromagnetic radiation of high energy | 0 | 0 |
| Neutron (n) | A neutral particle from the nucleus | 0 | 1 |
Section 3 of 7Alpha decay
1Large unstable nucleus
- Large unstable nucleus Alpha emission usually happens in large nuclei with too many protons and neutrons.
2Alpha particle leaves
- Alpha particle leaves The nucleus emits 2 protons and 2 neutrons together as one alpha particle.
3Numbers change
- Numbers change The mass number falls by 4 and the atomic number falls by 2.
4New element
- New element Because the atomic number changes, a different element is formed.
Section 4 of 7Beta and gamma decay
Other emissions
Beta decay
- Beta decay Happens in nuclei with too many neutrons.
- A neutron changes into a proton and an electron;
- the electron is emitted at high speed.
- A neutron changes into a proton and an electron;
Effect of beta decay
- Effect of beta decay The mass number stays the same but the atomic number increases by 1, so a new element forms.
Gamma emission
- Gamma emission A nucleus with excess energy releases a gamma ray. This often follows alpha or beta decay.
Effect of gamma emission (HT only)
- Effect of gamma emission (HT only) The mass number and atomic number do not change;
- the nucleus just loses energy and becomes more stable.
Section 5 of 7Worked example
1
Radium-226 (atomic number 88) emits an alpha particle.
2
The mass number drops by 4: 226 − 4 = 222.
3
The atomic number drops by 2: 88 − 2 = 86.
4
Element 86 is radon, so the product is radon-222.
5
For beta decay of carbon-14 (atomic number 6), the mass number stays at 14 and the atomic number rises to 7, giving nitrogen-14.
Section 6 of 7Key terms
| Term | Meaning |
|---|---|
| Radioactive | Describes a substance containing unstable nuclei that emit radiation. |
| Alpha particle | Two protons and two neutrons, identical to a helium nucleus. |
| Beta particle | A fast-moving electron emitted from the nucleus when a neutron changes into a proton. |
| Gamma ray | High-energy electromagnetic radiation emitted by a nucleus. |
| Mass number | The total number of protons and neutrons in a nucleus. |
| Atomic number | The number of protons in a nucleus. |
Section 7 of 7Exam technique
1
Saying that beta particles are electrons from the electron shells. They are produced in the nucleus when a neutron turns into a proton.
2
Writing that gamma emission changes the element. Gamma rays carry away energy only, so the numbers stay the same.
3
Thinking decay can be sped up by heating the sample. Decay rate is unaffected by conditions.
4
Forgetting that alpha decay lowers the mass number by 4 and the atomic number by 2.
5
Predicting exactly which nucleus will decay next. Decay is random; only probabilities can be given.
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