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What is ionising radiation?

  • Ionising radiation has existed since the Universe formed and is naturally present in our environment here on Earth and is produced and used for specific purposes by humans
Applications radiation
  • Ionising radiation is an electromagnetic wave with very high frequency – higher than radio waves used for broadcasting, microwaves used in cooking, and visible light.

    Source: Radiation: Effects and Sources, UNEP, 2016
  • Ionising radiation gets its name from the fact that it has sufficient energy to break atomic structures and so remove electrons from chemicals leaving them in a charged state.
  • Ionising radiation comes in different forms, some are produced when radioactive elements decay, others can be produced by equipment such as x-ray sets and linear accelerators used in medical procedures.
  • The main types of ionising radiation are known as gamma-rays, beta-particles and alpha-particles


Units measure
  • Radioactive elements decay at specific rates, and this rate of decay is measured in Bequerels (Bq) defined as the disintegration of one atom (and thereby emitting a radioactive particle) per second. Ionising radiation exposure is measured by the ‘absorbed dose’, the energy deposited per unit mass, and expressed in the units Gray (Gy, 1Gy represents one joule of energy deposited in a kilogram of mass).  For radiation protection, the measure ‘effective dose’ is often used, measured in Sieverts (Sv).  Effective doses are the absorbed doses weighted to reflect the differing effectiveness of different types of radiation and differing sensitivity of the different organs of the body.  In practice exposures of people are in the range of thousandths (milli-, m) or millionths (micro-, µ) - that is mGy/mSv or µGy/µSv 

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