Radioactive substances give out radiation all of the time. There are three types of nuclear radiation: alpha, beta and gamma. Alpha is the least penetrating, while gamma is the most penetrating.

Radiation can be harmful, but it can also be useful. The uses of radiation include smoke detectors, paper-thickness gauges, treating cancer and sterilising medical equipment.

Types of radiation

Nuclear radiation comes from the nucleus of an atom. Substances that give out radiation are said to be radioactive. There are three types of nuclear radiation:

• alpha
• beta
• gamma

Radiation can be absorbed by substances in its path. For example, alpha radiation travels only a few centimetres in air, beta radiation travels tens of centimetres in air, while gamma radiation travels many metres. All types of radiation become less intense the further the distance from the radioactive material, as the particles or rays become more spread out.

The thicker the substance, the more the radiation is absorbed. The three types of radiation penetrate materials in different ways

Alpha radiation

Alpha radiation is the least penetrating. It can be stopped (or absorbed) by a sheet of paper.

Beta radiation

Beta radiation can penetrate air and paper. It can be stopped by a thin sheet of aluminium.

Gamma radiation

Gamma radiation is the most penetrating. Even small levels can penetrate air, paper or thin metal. Higher levels can only be stopped by many centimetres of lead, or many metres of concrete.

Check your understanding by having a go at this animation. Click on each image of the rock to discover the reading on the radiation meter. Use the readings to confirm that the rock gives out beta radiation

Ionisation

Nuclear radiation ionises materials. This changes atoms or molecules into charged particles.

Uses of alpha radiation

Ionisation is useful for smoke detectors. Radioactive americium releases alpha radiation, which ionises the air inside the detector. Smoke from a fire absorbs alpha radiation, altering the ionisation and triggering the alarm.

Uses of beta radiation

Beta radiation is used for tracers and monitoring the thickness of materials.

Doctors may use radioactive chemicals called tracers for medical imaging. Certain chemicals concentrate in different damaged or diseased parts of the body, and the radiation concentrates with it. Radiation detectors placed outside the body detect the radiation emitted and, with the aid of computers, build up an image of the inside of the body.

Radiation is used in industry in detectors that monitor and control the thickness of materials such as paper, plastic and aluminium. The thicker the material, the more radiation is absorbed and the less radiation reaches the detector. It then sends signals to the equipment that adjusts the thickness of the material. Check your understanding of this by watching the simulation.

Uses of gamma radiation

Gamma radiation is used in the treatment of cancer, testing equipment and sterilising medical instruments.

Radiation is all around us. It comes from radioactive substances including the ground, air, building materials and food. Radiation is also found in cosmic rays from space

You cannot do much to reduce your exposure to natural background radiation, but great care is needed when handling radioactive materials. Precautions include:

• wearing protective clothing
• keeping as far away as is practicable - for example, by using tongs
• keeping your exposure time as short as possible, and
• keeping radioactive materials in lead-lined containers, labelled with the appropriate hazard symbol.

Waste

Low-level radioactive waste, such as contaminated gloves, can be disposed of in landfill sites. But higher level waste, which may be dangerously radioactive, is difficult to dispose of. It can be reprocessed to extract nuclear fuel, or encased in glass and left deep underground.

When an atom or molecule is ionised:

• electrons may be removed to form positively charged particles, or
• electrons may be gained to form negatively charged particles.