Radioactivity and particles takes you inside the atom itself. This section of the Edexcel IGCSE Science Single Award covers the nature of radioactive decay, the properties of different types of radiation, and the energy-releasing processes of nuclear fission and fusion.
The edexcel igcse science single award physics: radioactivity and particles section of the 4SS0 specification addresses three topics: units, radioactivity, and fission and fusion. The material is terminology-heavy, but the underlying principles are coherent: atoms can be unstable, unstable atoms emit radiation to become more stable, and nuclear processes release far more energy than chemical processes. These edexcel igcse science single award revision notes present each topic with the precision the examination demands.
Units
| Quantity | Unit | Symbol |
|---|---|---|
| Activity | becquerel | Bq |
| Half-life | second (or appropriate time unit) | s |
| Distance (penetration) | centimetre | cm |
| Time | second / minute / hour | s / min / h |
Activity is the number of nuclear decays per second. One becquerel equals one decay per second. Half-life may be expressed in seconds, minutes, hours, days or years depending on the isotope.
Radioactivity
Atomic structure
An atom consists of a central nucleus containing protons and neutrons, surrounded by orbiting electrons. The atomic number (also called the proton number) is the number of protons in the nucleus. The mass number (also called the nucleon number) is the total number of protons and neutrons. Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. The notation for a nucleus uses the mass number as a superscript and the atomic number as a subscript to the left of the element symbol.
Types of radiation
Some isotopes are unstable and undergo radioactive decay, emitting ionising radiation in a random process. There are three types of nuclear radiation:
| Property | Alpha (α) | Beta (β) | Gamma (γ) |
|---|---|---|---|
| Nature | 2 protons + 2 neutrons (helium nucleus) | High-speed electron from the nucleus | Electromagnetic wave (very short wavelength) |
| Charge | +2 | -1 | 0 |
| Mass (relative) | 4 | Very small (about 1/2000 of a proton) | 0 |
| Penetrating power | Stopped by paper or a few cm of air | Stopped by a few mm of aluminium | Reduced by thick lead or several cm of concrete |
| Ionising power | Strongly ionising | Moderately ionising | Weakly ionising |
Background radiation
Background radiation is ionising radiation that is present all around us from natural and man-made sources. Natural sources include: radon gas from rocks and soil (the largest single contributor), cosmic rays from space, radioactive isotopes in food and drink, and radioactive minerals in the ground. Man-made sources include medical procedures (X-rays, radiotherapy) and fallout from past nuclear weapons tests. Any measurement of radioactivity from a source must account for background radiation by subtracting its count rate from the measured count rate.
Half-life
The half-life of a radioactive isotope is the time taken for half of the undecayed nuclei in a sample to decay (or equivalently, the time for the activity to halve). Half-life is different for different isotopes: some have half-lives of fractions of a second, while others have half-lives of billions of years. The half-life of a given isotope is constant and cannot be changed by physical or chemical means.
Number of half-lives = 18 / 6 = 3
After 1 half-life: 800 / 2 = 400 Bq
After 2 half-lives: 400 / 2 = 200 Bq
After 3 half-lives: 200 / 2 = 100 Bq
The activity after 18 hours is 100 Bq.
Uses of radioactivity
Radioactive isotopes have uses in both industry and medicine. In medicine, gamma radiation is used in radiotherapy to destroy cancer cells, and radioactive tracers are used in diagnostic imaging. In industry, beta or gamma sources are used to monitor the thickness of materials on production lines, and gamma sources are used to sterilise medical equipment. The choice of radiation type depends on the application: the penetrating power and half-life must match the requirements of the task.
Contamination and irradiation
Contamination occurs when a radioactive material is deposited on or inside an object or person. The material continues to emit radiation from its new location, posing an ongoing risk. Irradiation occurs when an object or person is exposed to radiation from an external source but does not become radioactive itself. Once the source is removed, the irradiation stops. The distinction matters because contamination requires decontamination (removing the radioactive material), while irradiation simply requires removing the person or object from the area near the source.
Dangers and safety
Ionising radiation can cause mutations in living cells, damage tissue, and increase the risk of cancer. The dangers are managed by: keeping sources in lead-lined containers, using tongs or robotic handlers to maintain distance, limiting exposure time, and wearing appropriate shielding. Radioactive waste disposal is a significant challenge: high-level waste remains dangerous for thousands of years and must be stored securely in deep geological repositories.
Fission and fusion
Nuclear fission
Fission is the splitting of a large, unstable nucleus into two smaller nuclei (called daughter nuclei), releasing energy and a small number of neutrons. The most commonly examined example is uranium-235 (U-235). When a neutron collides with a U-235 nucleus, the nucleus becomes unstable and splits. The energy is released as kinetic energy of the fission products (the daughter nuclei and neutrons move apart at high speed).
The emitted neutrons can go on to cause further fission events, creating a chain reaction. In a nuclear reactor, this chain reaction is controlled so that it proceeds at a steady rate. Shielding around the reactor absorbs radiation and protects workers and the environment.
Nuclear fusion
Fusion is the joining of two small nuclei to form a larger nucleus, releasing energy. Fusion is the energy source for stars: in the Sun, hydrogen nuclei fuse to form helium, releasing the energy that powers the star's radiation. Fusion requires extremely high temperatures (millions of degrees) to overcome the electrostatic repulsion between the positively charged nuclei.
Why nuclear reactions release so much energy
Both fission and fusion release energy because the total mass of the products is slightly less than the total mass of the reactants. This lost mass is converted into energy according to Einstein's famous relationship E = mc2. Because the speed of light (c) is an enormous number (3 × 108 m/s), even a tiny loss of mass produces an immense amount of energy. This is why nuclear reactions release millions of times more energy per atom than chemical reactions, which only rearrange electrons without changing the nucleus.
The practical consequence is that a small amount of nuclear fuel can produce the same energy as a very large amount of fossil fuel. A single kilogram of uranium fuel can release as much energy as burning several thousand tonnes of coal. This energy density is both the advantage and the challenge of nuclear power: the energy output is enormous, but so is the responsibility of managing the radioactive waste.
Common mistakes
- Confusing half-life with the time for all the material to decay: After one half-life, half the original material remains. After two half-lives, one quarter remains. The material never fully decays; it just becomes negligible.
- Saying alpha is the most dangerous because it is the most ionising: Context matters. Outside the body, alpha is the least dangerous because it cannot penetrate the skin. Inside the body (if ingested or inhaled), alpha is the most dangerous precisely because it ionises so heavily in a small area of tissue.
- Confusing fission and fusion: Fission splits a large nucleus. Fusion joins small nuclei. Both release energy, but the processes are opposite. Fission is used in nuclear power stations. Fusion powers stars.
Self-check questions
Use these edexcel igcse science single award practice questions to test your understanding of physics: radioactivity and particles edexcel igcse content.
- State the three types of nuclear radiation and compare their penetrating powers.
- A sample has an activity of 1,200 Bq and a half-life of 4 days. Calculate the activity after 12 days.
- Explain the difference between contamination and irradiation.
- Describe the process of nuclear fission of U-235 and explain how a chain reaction can occur.
- State what provides the energy source for stars and name the nuclear process involved.
For question 2: 12 days = 3 half-lives. 1,200 to 600 to 300 to 150 Bq. The activity after 12 days is 150 Bq.
These edexcel igcse science single award notes on igcse 4ss0 physics: radioactivity and particles cover every specification point. The exam will test your knowledge of radiation types, half-life calculations, and the distinction between fission and fusion. Solid recall of these edexcel igcse science single award explained concepts, combined with careful attention to the precise definitions, will serve you well on the Green Bridge CBT platform and in the examination itself.
Revision notes for edexcel igcse science single award physics: radioactivity and particles covering decay, half-life, fission and fusion.
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