Radioactive Decay and Nuclear Radiation
Understand Radioactive Decay and Nuclear Radiation for GCSE Physics with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Unstable nuclei emit alpha, beta, gamma or neutron radiation, which differ in their range and penetrating power.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
Some atomic nuclei are unstable and give out radiation as they change to become more stable. This is a random process called radioactive decay.
Activity is the rate at which a source decays, measured in becquerels, where one becquerel is one decay per second. Count-rate is the number of decays recorded per second by a detector such as a Geiger-Muller tube.
Four types of nuclear radiation must be known. An alpha particle is two protons and two neutrons, the same as a helium nucleus. A beta particle is a high speed electron ejected from the nucleus. Gamma is electromagnetic radiation from the nucleus. A neutron may also be emitted.
Revision notes
Radioactive decay
Unstable nuclei give out radiation as they change to become more stable.
The process is random: it is impossible to predict which nucleus will decay next, or when a particular nucleus will decay. Only the overall rate can be predicted.
Activity and count-rate
Activity is the rate at which a source of unstable nuclei decays, measured in becquerels.
One becquerel is one decay per second. Count-rate is the number of decays recorded each second by a detector such as a Geiger-Muller tube.
The four radiations
Alpha: two protons and two neutrons, the same as a helium nucleus.
Beta: a high speed electron ejected from the nucleus as a neutron turns into a proton. Gamma: electromagnetic radiation from the nucleus. A neutron may also be emitted.
Key points
- Unstable nuclei decay to become more stable.
- Radioactive decay is a random process.
- Activity is measured in becquerels.
- One becquerel is one decay per second.
- An alpha particle is a helium nucleus.
- A beta particle is a high speed electron from the nucleus.
Worked examples
Example 1
State what an alpha particle consists of. [2 marks]
Model answer
Two protons and two neutrons (1 mark), which is the same as a helium nucleus (1 mark).
Example 2
Explain what is meant by saying radioactive decay is a random process. [2 marks]
Model answer
It is impossible to predict which nucleus in a sample will decay next (1 mark), or when a particular nucleus will decay (1 mark).
Example 3
Define activity and state its unit. [2 marks]
Model answer
Activity is the rate at which a source of unstable nuclei decays (1 mark), measured in becquerels, where one becquerel is one decay per second (1 mark).
Common mistakes
Saying a beta particle comes from the electron shells.
It is emitted from the nucleus when a neutron changes into a proton.
Saying decay can be predicted for individual nuclei.
The process is random; only the overall rate is predictable.
Confusing activity with count-rate.
Activity is the actual decay rate; count-rate is what a detector records.
Saying gamma is a particle.
Gamma is electromagnetic radiation, not a particle.
Exam tips
- Describe an alpha particle as two protons and two neutrons.
- Say emitted from the nucleus when describing beta.
- Define randomness in terms of unpredictability for individual nuclei.
- State becquerels as the unit of activity.
Key terms
- Radioactive decay
- The random emission of radiation from unstable nuclei.
- Activity
- The rate of decay, in becquerels.
- Count-rate
- The decays per second recorded by a detector.
- Geiger-Muller tube
- A detector used to measure count-rate.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.