What is radiation?
Australians are exposed to radiation from a variety of natural and artificial sources everyday. Radiation is energy travelling as waves or particles. Ionising radiation has enough energy to ionise (remove an electron from an atom) which can change the chemical composition of the material. Non-ionising radiation has less energy but can still excite molecules and atoms causing them to vibrate faster.
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Ionising radiation is produced from natural and artificial radioactive materials. It is present in the environment because naturally occurring radioactive materials such as uranium, thorium, actinium and potassium-40 exist in the material that makes up planet Earth. This leads to exposure to alpha, beta and gamma radiation including radioactive radon gas. Natural radioactivity is present in the air we breathe, food we eat, water we drink and even in our bodies. We are also exposed to natural ionising radiation that comes from outer space and passes through the atmosphere of the planet. This is called cosmic radiation.
There are three main sources of artificial ionising radiation. They are:
- medical uses including diagnosis of many diseases and treatment of cancer
- industrial uses, mainly in measurement and scientific research
- fallout from nuclear weapons testing and accidents around the world.
The figure below shows the relative annual per capita dose to the Australian population from the various radiation sources. Currently, on average, our exposure to medical radiation is the dominant source.
The damaging effects of ionising radiation come from the packages of high energy that are released from radioactive sources. Although different types of ionising radiation have different patterns of energy release and penetrating power (see ionising radiation topics), there is no general property that makes artificial ionising radiation different or more damaging than the ionising radiation that comes from natural radioactive material. While the sources differ, the types of radiation are the same which means we can directly compare doses from artificial sources of ionising radiation to those from natural sources.
Solar radiation consists of several different forms of non-ionising radiation, such as ultraviolet (UV). Many modern technologies such as power-lines, electrical equipment and mobile phone systems also produce forms of non-ionising radiation.
We cannot eliminate radiation from our environment, but by having a good understanding of radiation and how to control our exposure, we can reduce our risk.
The electromagnetic spectrum includes radio waves, microwaves, infrared rays, light rays, UV rays, X‑rays and gamma rays. All electromagnetic radiation is transmitted through empty space at the speed of light.
The different forms of electromagnetic radiation are distinguished from each other by:
- their wavelength
- the amount of energy they transfer.
These properties also determine their ability to travel through objects, their heating effects and their effect on living tissue.
Sometimes electromagnetic radiation is described using its frequency rather than its wavelength. These two characteristics are related.
If we could watch a wave of electromagnetic radiation pass, the wavelength would be the distance between two adjacent wave crests, while the frequency would be the number of wave peaks that pass in a given time. Since electromagnetic radiation travels at a constant speed in a constant environment, radiation with a longer wavelength would have fewer waves passing in a given time (lower frequency) and radiation with a shorter wavelength would have more waves passing in a given time (higher frequency). When wavelength increases, frequency decreases and vice versa.
The hertz is the unit used to measure frequency. A measured frequency of one hertz (Hz) represents one wavelength per second or one cycle per second. The range of frequencies within the electromagnetic spectrum is large, resulting in the common use of a series of units:
- one kilohertz(kHz) is one thousand hertz (1000 Hz)
- one megahertz(MHz) is one million hertz (1,000,000 Hz)
- one gigahertz(GHz) is one thousand million hertz (1,000,000,000 Hz).