What are alpha, beta and gamma radiation, and how do nuclei change when they decay?
Alpha, beta and gamma radiation and their properties, the random nature of decay, and writing balanced nuclear equations for alpha and beta decay.
A CCEA GCSE Physics answer on the nature and properties of alpha, beta and gamma radiation, the random nature of radioactive decay, and how to balance nuclear equations for alpha and beta decay.
Reviewed by: AI editorial process; not yet individually human-reviewed
Have a quick question? Jump to the Q&A page
Jump to a section
What this dot point is asking
CCEA wants you to describe alpha, beta and gamma radiation and their properties, explain that radioactive decay is random and spontaneous, and write balanced nuclear equations for alpha and beta decay. The penetration table and balancing equations are common questions.
The answer
Why nuclei decay
The three types of radiation
The more ionising a radiation, the more damage it does to cells but the shorter its range.
Nuclear equations
Worked example: beta decay
Examples in context
- Example 1. A smoke detector
- A weak alpha source ionises the air in the detector, allowing a small current. Smoke absorbs the alpha radiation, the current drops, and the alarm sounds. Alpha is ideal because its short range keeps it safely inside the detector.
- Example 2. Background radiation
- We are all exposed to low-level background radiation from rocks (such as radon gas), cosmic rays, food and medical sources. This must be subtracted from a count rate to find the true activity of a source.
- Example 3. Choosing a radiation by penetration
- A radiographer uses the penetration of each type to decide its use. Alpha, stopped by paper, is kept inside sealed detectors; beta, stopped by thin metal, is used in thickness gauges; gamma, which passes through the body, is used in scans and to treat tumours from outside.
A reliable way to recall the properties is to remember that penetration and ionising power run in opposite orders. Alpha is the most ionising but least penetrating, gamma is the least ionising but most penetrating, and beta sits in between. This pattern explains both the hazards and the uses of each type.
Try this
Q1. What is an alpha particle made of? [1 mark]
- Cue. A helium nucleus: 2 protons and 2 neutrons.
Q2. Which radiation is the most penetrating? [1 mark]
- Cue. Gamma radiation.
Q3. In alpha decay, how do the mass number and atomic number change? [2 marks]
- Cue. Mass number falls by 4; atomic number falls by 2.
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA style4 marksCompare alpha, beta and gamma radiation in terms of what they are made of and their penetrating power.Show worked answer →
Alpha is a helium nucleus (2 protons and 2 neutrons); it is the most ionising and the least penetrating, stopped by paper or a few cm of air.
Beta is a fast-moving electron; it is moderately ionising and penetrating, stopped by a few mm of aluminium.
Gamma is a high-energy electromagnetic wave; it is the least ionising and most penetrating, reduced by thick lead or concrete.
Markers reward correct nature and penetration for all three: alpha helium nucleus, stopped by paper; beta electron, stopped by aluminium; gamma EM wave, reduced by lead.
CCEA style3 marksA nucleus of radium-226 (atomic number 88) emits an alpha particle to become radon (Rn). Write the balanced nuclear equation for this alpha decay.Show worked answer →
Alpha decay reduces the mass number by 4 and the atomic number by 2:
The mass numbers balance (226 = 222 + 4) and the atomic numbers balance (88 = 86 + 2).
Markers reward the radon mass number 222, atomic number 86, the alpha particle written correctly, and balanced totals.
Related dot points
- The nuclear model of the atom, the charges and masses of protons, neutrons and electrons, atomic and mass number, and isotopes.
A CCEA GCSE Physics answer on the nuclear model of the atom, the relative charge and mass of protons, neutrons and electrons, atomic number and mass number, nuclide notation, and isotopes.
- Half-life as the time for activity to halve, reading half-life from a decay curve, and calculations of remaining activity or mass.
A CCEA GCSE Physics answer on the meaning of half-life, how to read a half-life from a decay curve, and how to calculate the activity or mass of a radioactive source remaining after a number of half-lives.
- Uses of radioactive sources in medicine and industry, the dangers of ionising radiation, irradiation versus contamination, and safety precautions.
A CCEA GCSE Physics answer on the uses of radioactive sources in medicine and industry, how the choice of source depends on its radiation and half-life, the dangers of ionising radiation, and the difference between irradiation and contamination.
- Nuclear fission of heavy nuclei and the chain reaction, the parts of a nuclear reactor, and nuclear fusion in stars.
A CCEA GCSE Physics answer on nuclear fission of heavy nuclei and the chain reaction, the role of fuel rods, control rods and the moderator in a reactor, and nuclear fusion in stars and why it needs extreme conditions.
Sources & how we know this
- CCEA GCSE Physics specification — CCEA (2017)