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Types of Radiation (Edexcel IGCSE Physics)
Revision Note
Types of radiation
- Some atomic nuclei are unstable and radioactive
- This is because of an imbalance of protons or neutrons in the nucleus
- Carbon-14 is an example of an isotope of carbon which is unstable
- This is because it has two extra neutrons compared to a stable nucleus of carbon-12
Stable and unstable isotopes of carbon
Carbon-12 is stable, whereas carbon-14 is unstable because it has two extra neutrons
- Unstable nuclei can emit radiation to become more stable
- Radiation can be in the form of a high-energy particle or wave
- This process is known as radioactive decay
- As the radiation moves away from the nucleus, it takes some energy with it
- This makes the nucleus more stable
Radioactive decay of a nucleus
Unstable nuclei decay by emitting high energy particles or waves
- When an unstable nucleus decays, it emits radiation
- The different types of radiation that can be emitted are:
- Alpha (α) particles
- Beta (β-) particles
- Gamma (γ) radiation
- These changes are spontaneous and random
Worked example
Which of the following statements is not true?
A Isotopes can be unstable because they have too many or too few neutrons
B The process of emitting particles or waves of energy from an unstable nucleus is called radioactive decay
C Scientists can predict when a nucleus will decay
D Radiation refers to the particles or waves emitted from a decaying nucleus
ANSWER: C
- Answer A is true. The number of neutrons in a nucleus determines the stability
- Answer B is true. This is a suitable description of radioactive decay
- Answer D is true. Radiation is about emissions. It is different to radioactive particles
- Answer C is not true
- Radioactive decay is a random process
- It is not possible to predict precisely when a particular nucleus will decay
Examiner Tip
The terms unstable, random and decay have very particular meanings in this topic. Remember to use them correctly when answering questions!
Properties of alpha, beta and gamma radiation
Alpha particles
- The symbol for alpha is α
- An alpha particle is the same as a helium nucleus
- This is because it consists of two neutrons and two protons
Beta particles
- The symbol for beta is β−
- Beta particles are high-energy electrons
- They are produced in nuclei when a neutron changes into a proton and an electron
Gamma rays
- The symbol for gamma is γ
- Gamma rays are electromagnetic waves
- They have the highest energy of the different types of electromagnetic waves
Alpha, beta & gamma radiation
Alpha particles, beta particles and gamma waves can be emitted from unstable nuclei
Properties of alpha, beta & gamma
- Alpha (α), beta (β) and gamma (γ) radiation can be identified by their:
- Nature (what type of particle or radiation they are)
- Ionising ability (how easily they ionise other atoms)
- Penetrating power (how far can they travel before they are stopped completely)
- Alpha, beta and gamma penetrate materials in different ways
- This means they are stopped, or reduced, by different materials
Penetrating power of alpha, beta and gamma
Alpha, beta and gamma are different in how they penetrate materials. Alpha is the least penetrating, and gamma is the most penetrating
- Alpha is stopped by paper, whereas beta and gamma pass through it
- Beta is stopped by a few millimetres of aluminium
- Gamma rays can pass through aluminium but are only partially stopped by thick lead
Summary of the properties of nuclear radiation
| Particle | Nature | Range in air | Penetrating power | Ionising ability |
| Alpha (α) |
helium nucleus (2 protons, 2 neutrons) |
a few cm | low; stopped by a thin sheet of paper | high |
| Beta (β) | high-energy electron | a few 10s of cm | moderate; stopped by a few mm of aluminium foil or Perspex | moderate |
| Gamma (γ) | electromagnetic wave | infinite | high; reduced by a few cm of lead | low |
Worked example
A student has an unknown radioactive source. They are trying to work out which type of ionising radiation is being emitted.
They measure the count rate, using a Geiger-Muller tube, when the source is placed behind different materials. Their results are recorded in a table.
| no material between source and detector | thin sheet of paper between source and detector | 5 mm aluminium foil between source and detector | 5mm lead plate between source and detector | |
| Count-rate | 4320 | 4218 | 256 | 34 |
Which type(s) of ionising radiation is/are emitted by the source?
A Alpha particles
B Beta particles
C Gamma rays
D Alpha, beta and gamma radiation
ANSWER: B
- The answer is not A or D because the radiation passed through the paper almost unchanged
- This means it is not alpha as alpha is stopped by a thin sheet of paper
- The answer is not C because the aluminium decreased the count rate significantly
- This means it is not gamma as gamma penetrates aluminium
- Therefore, the source must be beta particles
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