Natural and Artificial Ionizing Radiation

We can classify radiation into ionizing and non-ionizing radiation, according to the effects it produces on matter.Ionizing radiation includes cosmic rays, X rays and the radiation from radioactive materials.Non-ionizing radiation includes ultraviolet light, radiant heat, radio waves and microwaves.In medical practice ultrasound and magnetic resonance imaging (MRI) involve non-ionizing radiation.© PhotoDisk

Cosmic rays reach the Earth from outer space. They are mainly protons (positive charged particles) of uncertain origin and very high energies that reach our atmosphere in fairly constant numbers. © PhotoDisk

The Earth itself is also radioactive and all materials in the Earth’s crust contain radionuclides. Indeed, energy from natural activity deep in the Earth contributes to the shaping of the crust and the maintenance of internal temperatures. This energy comes mainly from the decay of the radioactive isotopes of uranium, thorium and potassium.© IAEA / P. Waggitt

Our bodies naturally contain radioactive materials such as carbon-14, potassium-40 and polonium-210.Lead-210 and polonium-210 are present in air, food, and water, and so irradiate the body internally. Potassium-40, which also comes into the body with a normal diet, is the main source of internal irradiation apart from the radon decay products. In addition, the interactions of cosmic rays with the atmosphere create a number of radionuclides, such as carbon-14, which also contribute to internal irradiation. © Stock Images / Zefa

ALTITUDE — Pople living at considerable altitude may receive annual doses several times higher than those people living at sea level.LATITUDE — Some protons with lower energies come from the sun and are given off in bursts during solar flares. Protons are charged particles, so the number entering the atmosphere is affected by the Earth’s magnetic field — more come in near the poles than the equator. As such, the dose rate also increases with latitude.© PhotoDisk

NATURAL SOURCES — Cosmic rays, gamma rays from the Earth, radon decay products in the air, and various radionuclides found naturally in food and drink.ARTIFICIAL SOURCES — X rays, fallout from the testing of nuclear weapons in the atmosphere, discharges of radioactive waste from the nuclear industry, industrial gamma rays, and miscellaneous items such as consumer products.Compiled from data in Tables 1 and 2 of UNSCEAR 2000 Report to the UN General Assembly.© IAEA / A. Diesner-Kuepfer

DIAGNOSTIC RADIOLOGY — The use of X rays for examining patients. Radiation from a machine passes through the patient. X rays penetrate flesh and bones to different degrees and produce images of the internal structures of the body on photographic film. Doses are fairly low.CT scans: A fan-shaped beam of X rays is rotated around the patient and registered on the opposite side of the machine by a row of detectors. An image of a slice or section through the patient is then reconstructed by a computer. CT scans convey superior diagnostic information. However, doses can be an order of magnitude or more higher than those from conventional X ray examinations.© PhotoDisk

NUCLEAR MEDICINE — The use of pharmaceuticals labelled with radionuclides for diagnosis or therapy. For a diagnostic procedure in nuclear medicine, the patient is given a radionuclide that is naturally taken up by the tissue or organ under study. Administration may be by injection, ingestion, or inhalation. As the radionuclide emits gamma rays, an image of the tissue or organ under study is taken.Individual doses from radionuclide scans are comparable to those in diagnostic radiology.© IAEA

RADIOTHERAPY — The use of radiation beams to treat patients.A beam of high energy X rays, gamma rays or electrons is directed towards the diseased tissue so as to give it a high dose while sparing the surrounding healthy tissue. If a tumour is deep in the body, the beam is pointed at it from several directions so as to reduce the incidental damage. Another form of treatment called brachy- therapy, in which a radiation source is placed in or on the body for a short period, is used for some cancers. As radiotherapy doses are strong, such treatment is only used when the outlook for a cure or relief is good and when other methods of treatment would be less effective.© A.Leuker / IAEA

COMMON USES OF RADIATION IN INDUSTRY — Radiography of welds and joints. Security inspection of bags and parcels. Level gauging of container contents.Sterilization of some medical supplies. Static elimination in paper production. Analysis of specimens for quality control. © IAEA

When nuclear weapons were tested above ground, they propelled a variety of radionuclides from hydrogen-3 (tritium) to plutonium-241 into the upper atmosphere. From there, the radionuclides transferred slowly to the lower atmosphere and then to the Earth’s surface.Around 500 atmospheric explosions were conducted before the limited test ban treaty was enacted in 1963. The last atmospheric nuclear explosion took place in 1980.© IAEA / V. Mouchkin

An explosion in a nuclear reactor at the Chernobyl nuclear power plant on 26 April 1986 caused the release of substantial quantities of radionuclides during a period of ten days.Airborne material was dispersed throughout Europe from the site in Ukraine. As the contaminated air spread throughout Europe and beyond, local weather conditions largely determined where the radionuclides were to fall. Rainfall caused more radionuclides to be deposited in some areas rather than others.© IAEA / V. Mouchkin

Radionuclides of artificial origin are discharged to the environment by the nuclear power industry, military establishments, research organizations, hospitals and general industry.Discharges of any significance should be subject to statutory control; they must be authorized and monitored. Owners or operators of the facilities from which radionuclides are discharged carry out monitoring programmes, as do some regulatory agencies. Accidents involving radioactive sources can be prevented by ensuring that only those who are properly qualified and trained use and look after the sources.© IAEA / P. Pavlicek

Munitions using depleted uranium (DU) were used during several modern conflicts.DU is a by-product of the uranium fuel cycle where natural uranium is enriched to provide suitable fuel for nuclear power. It is called depleted because it has had most of its uranium-235 isotope removed.Depleted uranium in munitions is in a concentrated metallic form. It is not dangerous because of its radioactivity but because it is a heavy metal.© IAEA / A. Bleisel

Areas in various parts of the world have become contaminated with radionuclides as a result of human activities.In cases where the level of contamination is high, measures might be needed to ensure that the area is safe for people to live or use for other purposes.For small areas, it might be possible to do this by removing contaminated soil and other materials, but for large areas the amount of material involved would be too large. © IAEA / V. Mouchkin

PUBLIC ANXIETY — The greatest concern about ionizing radiation stems from its potential to cause malignant diseases in people exposed to it and inherited defects in later generations.The likelihood of such effects depends on the amount of radiation that a person receives, whether from a natural or an artificial source. As the effects of ionizing radiation have become better understood during recent decades, a system of radiological protection has been developed to protect people from exposure to sources of radiation.© PhotoDisk

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