Radiation Safety

Types of Radiation

Radiation comes from atoms. An atom may undergo a transformation naturally or artificially. During this process, it emits energy in the form of a wave (ray) or particles.

This energy produced is known as radiation. Radiation has a wide range of energies and forms the electromagnetic spectrum. The spectrum has two major divisions:
  • Non-ionizing Radiation. Non-ionizing radiation has enough energy to move atoms in a molecule around or cause them to vibrate, but not enough to remove electrons. Some of this radiation does have enough energy to cause other effects that can be harmful. Examples of this kind of radiation include sound waves, visible light, and microwaves.
  • Ionizing Radiation. Ionizing radiation, the type of radiation familiar to most people, has enough energy to remove tightly bound electrons from atoms. Benefits include the generation of electric power, radiation therapy to kill cancer cells, and in diagnostic radiology such as nuclear medicine.
Ionizing radiation has two main components: Short-wave-length electromagnetic radiation (X-rays and gamma-rays) and subatomic particles (usually, alpha particles, electrons, positrons, and neutrons). Ionization, the process whereby a tightly bound electron is removed from an atom, occurs when a neutral atom has an interaction with a passing charged particle, gamma photon, positron, or electron that causes one or more of the orbital electrons of the atom to be ejected, leaving the atom charged.
The energy of the radiation shown on the electromagnetic spectrum increases from left to right as the frequency rises.
Radiation Safety

Exposure To Ionizing Radiation

Exposure to ionizing radiation can be produced by naturally occurring or man-made sources. The Canadian Nuclear Safety Commission (CNSC) has instituted a limit of 1 milliSievert (mSv) of ionizing radiation exposure over a one year period to members of the public who are occupationally exposed. The 1 mSv limit is based on international recommendations. (It does not account for exposure from natural radiation sources or medical diagnosis or treatment.) Visit the CNSC website for additional information on its programs.

Natural Background Radiation

It’s important to remember that we are continually exposed to ionizing radiation from natural sources.  The main constituents of this natural background radiation are:
  • Cosmic rays from outer space which reach the Earth
  • Radioactive substances in the Earth’s crust
  • Trace amounts of radioactivity in the body
When the Earth was formed, many of its elements were radioactive.  Over the millennia, radioactivity decayed until only those isotopes with extremely long half lives of 100 million years or more and their decay products are found in the Earth’s crust. The following table lists the estimated average annual effective doses of radiation from natural sources.
Annual Doses from Natural Background Radiation
Source of exposure Average annual effective dose (mSv)
Global radiation exposure Areas of typically elevated radiation exposures*
Cosmic rays (outer space) 0.39 2.0
Terrestrial gamma rays (Earth’s crust) 0.46 4.3
Radionuclides in the body (except radon) 0.23 0.6
Radon and its decay products 1.3 10
Total (rounded) 2.4 ~
*Some of these are areas in Brazil, India, Kenya, Iran, the central region of France and Niue Island.
~Source: International Commission on Radiological Protection – ICRP 82, 1999

Man-Made Radiation

Man-made sources of radiation include medical x-rays, colour TVs, and smoke detectors. Three or four chest X-rays can contribute approximately 1 mSv to an individual’s exposure. Given that the protective atmosphere is thinner at higher altitudes, figures from the World Health Organization have determined that commercial airline crew members (pilots and flight attendants) who fly 600 hours-800 hours per year are exposed to an additional 2 mSv – 5 mSv annually in addition to other natural and man-made sources of radiation.
The following table lists the estimated average annual effective doses of radiation from man-made sources.More information on radiation doses from medical testing can be found at the Health Physics Society Web site.
Annual Doses of Radiation from Man-Made Sources
Source Average annual effective dose (mSv)
Medical x-rays 0.4
Living in stone, brick, or concrete building 0.07
Watching TV 0.01
Airline flight (per 1,000 miles flown) 0.01
Computer terminal 0.001
Smoke detector 0.00008
SOURCE: U.S. Environmental Health Protection Agency
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