FROM DENTAL X-RAYS TO NUCLEAR REACTORS: EVERYTHING YOU NEED TO KNOW ABOUT IONISING RADIATION, ITS USES AND HAZARDS

Words by Andrew May

For many, the word ‘radiation’ can set alarm bells ringing. If you think of the terrible death toll of the Hiroshima and Nagasaki bombs, or the devastating environmental effects of the Chernobyl nuclear disaster, it’s easy to see why. Events like these show just how lethal radiation can be. But radiation is around us all the time – most of it completely harmless, and much of it positively beneficial.

In its broadest sense, radiation refers to any form of emitted energy that travels outwards – or radiates – from a source. It can take the form of streams of fast-moving particles, such as those emitted by radioactive materials, or of the electromagnetic (EM) waves generated when electrons jump from one energy level to another inside atoms. The heat and light we receive from the Sun come to us in the form of EM radiation, and life on Earth would be impossible without these particular forms of radiation.

There are other types of EM radiation that we can produce by technological means, such as radio for communication, microwaves for cooking or X-rays for medical imaging. Although these are created and used in different ways, they are all essentially the same type of wave, travelling from A to B at the same speed – the speed of light. The difference lies in wavelength and frequency. EM radiation has a spectrum ranging from radio waves at the low frequency, long-wavelength end to X-rays and gamma rays at the high frequency, short wavelength. Any kind of EM radiation can be dangerous if enough energy is pumped into it. You see hazard warnings on microwave ovens, for example, and on lasers – which are  simply an intense beam of light. But there’s a subtlety which makes the high-frequency end of the EM spectrum substantially more dangerous than the lower end. This stems from the fact that EM radiation is fundamentally bipolar – the so-called ‘wave-particle duality’. Although it travels from its source to its destination exactly as if it were a wave, when it gets there it passes on its energy as if it were packaged up in discrete particles, called photons. The higher the frequency, the more energy each photon carries. If you have a microwave beam and an X-ray beam with the same total energy, the microwave energy will be spread out over millions of times more photons.