What is radioactivity?
Nature
Everything in the world is made up of extremely small building blocks called atoms. Some unstable atoms change spontaneously to become more stable, and they release particles (alpha and beta) and electromagnetic energy (gamma rays) as they do so. This release is known as radioactivity.
Fig 1: Illustration of an atom (courtesy NDA)
Many substances, both natural and man-made, are radioactive: uranium, a naturally occurring element, is radioactive, and the sun gives off cosmic rays which enter the Earth’s atmosphere. Background radiation is around us all the time, coming from various sources, including the ground and the food we eat and drink, although some places have higher levels than others.
How do we use radioactivity
Radioactive materials are used to produce electricity in nuclear power stations. If enough of the right kind of uranium is assembled in a nuclear reactor, it produces heat which is used to create steam, which in turn drives the turbines, which generate electricity.
Radioactive materials have many other uses in medicine, industry, agriculture and research. For example, because radioactivity can be easily detected, radioactive tracers can be used to locate leaks in underground pipes. Other radioactive sources are used to sterilise medical equipment.
What are the health effects of radioactivity?
Radiation can damage the tissues in our bodies, causing burns, radiation sickness and cancer. Because of this, its use has to be carefully controlled. When people first began to work with radioactivity they did not realise that it could be harmful, and many became ill and died. Nowadays we know how to measure the dose received, and use shielding to protect ourselves and the environment from such dangers.
However, this ability to damage tissue can be useful in medicine: a precisely focussed beam of radiation can be used to destroy cancer cells in tumours.
How do we protect ourselves from radiation?
People can receive a radiation dose in many ways by eating or breathing in radioactive materials (perhaps for medical purposes) or by being exposed to external radiation. We can be protected from external radiation by various levels of shielding.
Fig 2: Illustration of radiation dose pathway (courtesy NDA)
The radiation given off by different radioactive substances can vary in a number of ways: its type, its intensity and how long it continues to be given off (half-life).
There are mainly three main types of radiation:
- Alpha (α) radiation can be the most harmful if breathed in or eaten. However, it can only travel about 5 cm in air and can be stopped by paper, clothing, etc.
- Beta (β) radiation is less harmful, but can travel further (about 20 cm in air) and is more penetrating. It passes through paper and needs a few millimetres of aluminium or a thin piece of lead to stop it.
- Gamma (γ) radiation is still potentially harmful and it can travel a long way through air, and is extremely penetrating: several centimetres of lead or metres of concrete are required to stop it. However, it gets weaker as you move away from the source.
Alpha and beta radiation are both made up of particles. Unlike them, gamma radiation is part of the electromagnetic spectrum that includes light, ultraviolet rays and X-rays.
Fig 3: Illustration of shielding from radioactivity (redrawn by Bell Design)
A nuclear reactor gives off all three types of radiation: its core is very radioactive. Workers are protected from this radiation by shielding the core with steel and concrete.
All radioactive materials (including the radioactive wastes produced by nuclear reactors, industry, medicine and defence agencies) require careful handling and monitoring to protect people and the environment.
Will radioactivity go away?
The amount of radioactivity given off by a radioactive substance will gradually decrease. This is called radioactive decay. The time it takes for the radioactivity to decrease by 50% is called the half-life. Different radioactive atoms have different half-lives: some can be a matter of seconds; some can be many thousands of years. So the amount of radioactivity will reduce as time goes on, but for some atoms this will take millions of years.
Fig 4: Graph of a radioactivity decay curve (courtesy NDA)
Further information
If you would like further information about radioactivity then you can look at the following web sites:
Page last modified: 27 June 2008
Page published: 12 June 2008