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The global average exposure of humans to ionizing radiation is about 3 mSv (0.3 rem) per year, 80% of which comes from nature. The remaining 20% results from exposure to human-made radiation sources, primarily from medical imaging. Average human-made exposure is much higher in developed countries, mostly due to CT scans and nuclear medicine.
Radiation exposure is a measure of the ionization of air due to ionizing radiation from photons. [1] It is defined as the electric charge freed by such radiation in a specified volume of air divided by the mass of that air. [ 1 ]
It was established solely to "define precisely the present exposure of the population of the world to ionizing radiation". A small secretariat, located in Vienna and functionally linked to the United Nations Environment Programme (UNEP), organizes the annual sessions and manages the preparation of documents for the committee's scrutiny.
Exposure can be from a source of radiation external to the human body or due to internal irradiation caused by the ingestion of radioactive contamination. Ionizing radiation is widely used in industry and medicine, and can present a significant health hazard by causing microscopic damage to living tissue.
The level of health risk is dependent on duration and the type and strength of irradiation. Penetrating radiation such as gamma rays, X-rays, neutrons or beta particles pose the greatest risk from an external source. Low penetrating radiation such as alpha particles have a low external risk due to the shielding effect of the top layers of skin.
In listing civilian radiation accidents, the following criteria have been followed: There must be well-attested and substantial health damage, property damage or contamination. The damage must be related directly to radioactive materials or ionizing radiation from a man-made source, not merely taking place at a facility where such are being used.
The exposure can originate from various sources, including natural sources. Most frequently the term refers to ionizing radiation , and to a level of radiation that will serve a specific purpose, rather than radiation exposure to normal levels of background radiation .
Background radiation is a measure of the level of ionizing radiation present in the environment at a particular location which is not due to deliberate introduction of radiation sources. Background radiation originates from a variety of sources, both natural and artificial.