Radiation simply means the emission (sending out) of energy from a source. It could be a speaker that emits sound waves, or the sun that emits heat and light. There are many different types of radiation.

Most radiation travels from its source as a wave – like the ripples on a pond surface when you drop a pebble into it. Some radiation has so much energy that it travels as particles. To picture the particles, put a little talcum powder in the palm of your hand, hold your palm out flat and blow the powder away from you.

Some forms of radiation, such as ultraviolet light from the sun, or radio waves from space, are natural. Others are generated by humans, such as radio waves for communication, microwaves for cooking and X-rays in medicine.

Some radiation, like sound waves, needs something to travel through, like air or water. Ultrasound is a medical imaging technique that uses sound waves in the range above human hearing. These sound waves travel into a patient’s body, and some of the waves bounce back when they reach different types of tissue.

Electromagnetic radiation

In electromagnetic radiation, the energy has electromagnetic properties. An electromagnetic wave doesn’t need anything to travel through. X-rays, light and microwaves are all forms of electromagnetic radiation that you might have heard of. The different types of electromagnetic radiation make up what is known as the electromagnetic spectrum.

Radio waves have the longest wavelength and the lowest energy. At the other end of the spectrum are gamma rays, which have the shortest wavelength and the highest energy – the shorter the wavelength, the higher the energy. It is these higher energy wavelengths that behave more like particles.

Magnetic resonance imaging (MRI) uses radio waves and strong magnetic fields to generate images of the body.

Ionising and non-ionising radiation

We can also divide radiation into two types – ionising and non-ionising. Ionising radiation has enough energy to knock electrons out of atoms. When you remove electrons from atoms, you create ions.

X-rays are a form of ionising radiation. If you break a bone you might have to have an X-ray taken. As the X-rays pass through your tissues and bones, they can knock electrons off the atoms that make up our DNA, causing damage to it. This is why we have to be very careful not to be exposed to too many X-rays.

Non-ionising radiation does not have the energy to knock electrons around. Non-ionising radiation includes visible light, infrared (heat), radio waves and microwaves.

    Published 23 July 2007