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Radiation Basics - Ionising and Non Ionising Radiation

Ionising radiation has more energy than non ionising radiation; enough to cause chemical changes by breaking chemical bonds.

What is the electromagnetic spectrum?

The electromagnetic spectrum includes radio waves, microwaves, infrared rays, light rays, ultra violet rays, X‑rays and gamma rays. All electomagnetic radiation is transmitted through empty space at 3.0 X 108 metres per second (300 thousand kilometres per second).

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.

Image depicting the electromagnetic spectrum - showing where different types of radiation fall within the spectrum and samples of sources of radiation

What is the relationship between wavelength and frequency?

Sometimes electromagnetic radiation is described using its frequency rather than its wavelength. These two characteristics are closely related.

If we could watch a wave of electromagnetic radiation pass, the wavelength would be the distance between two adjacent wave crests, the frequency would be the number of wave peaks that passed 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 visa versa.

Illustration of wavelength and frequency

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 electomagnetic spectrum is great 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)

What is non ionising radiation?

Non ionising radiation is found at the long wavelength end of the spectrum and may have enough energy to excite molecules and atoms causing then to vibrate faster. This is very obvious in a microwave oven where the radiation causes water molecules to vibrate faster creating heat.

Non ionising radiation ranges from extremely low frequency radiation, shown on the far left through the radiofrequency, microwave, and visible portions of the spectrum into the ultraviolet range.

Extremely low-frequency radiation has very long wavelengths (in the order of a thousand kilometres or more) and frequencies in the range of 100 hertz or less. Radiofrequencies have wavelengths of between 1 and 100 metres and frequencies in the range of 1 million to 100 million hertz. Microwaves that we use to heat food have wavelengths that are about 1 hundredth of a metre long and have frequencies of about 10 billion hertz.

What is ionising radiation?

Ionising radiation has more energy than non ionising radiation; enough to cause chemical changes by breaking chemical bonds. This effect can cause damage to living tissue.

Shorter wavelength ultraviolet radiation begins to have enough energy to break chemical bonds. X-ray and gamma ray radiation, which are at the upper end of electromagnetic spectrum, have very high frequencies (in the range of 100 billion billion hertz) and very short wavelengths (1 million millionth of a metre). Radiation in this range has extremely high energy. It has enough energy to strip electrons from an atom or, in the case of very high-energy radiation, break up the nucleus of the atom.

The process in which an electron is given enough energy to break away from an atom is called ionisation. This process results in the formation of two charged particles or ions: the molecule with a net positive charge, and the free electron with a negative charge.

Each ionisation releases energy which is absorbed by material surrounding the ionised atom. Compared to other types of radiation that may be absorbed, ionising radiation deposits a large amount of energy into a small area. In fact, the energy from one ionisation is more than enough energy to disrupt the chemical bond between two carbon atoms. All ionising radiation is capable, directly or indirectly, of removing electrons from most molecules.

There are three main kinds of ionising radiation:

Alpha particles and beta particles are not part of the electromagnetic spectrum; they are energetic particles as opposed to pure energy bundles (photons).

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