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Radioactive contaminationImage:Radiation warning symbol.svg Radioactive contamination is the uncontrolled distribution of radioactivematerial in a given environment.
Sources of contaminationRadioactive contamination is typically the result of a loss of control of radioactive materials during the production or use of radioisotopes. For example, if a radioisotope used in medical imaging is accidentally spilled, the material could be spread by people as they walk around. Radioactive contamination may also be an inevitable result of certain processes, such as the release of radioactive xenonin nuclear fuel reprocessing. In cases that radioactive material cannot be contained, it may be diluted to safe concentrations. Nuclear falloutis the distribution of radioactive contamination by a nuclear explosion. Containment is what differentiates radioactive material from radioactive contamination. Therefore, radioactive material in sealed and designated containers is not properly referred to as contamination, although the units of measurement might be the same. MeasurementRadioactive contamination may exist on surfaces or in volumes of material or air. In a nuclear power plant, detection and measurement of radioactivity and contamination is often the job of a Certified Health Physicist. Surface contaminationSurface contamination is usually expressed in units of radioactivity per unit of area. For SI, this is becquerelsper square metre(or Bq/m2). Other units such as dpm/cm2, picoCuries per 100 cm2, or disintegrations per minute per square centimetre(1 dpm/cm2 = 166 2/3 Bq/m2) may be used. Surface contamination may either be fixed or removable. (In the case of fixed contamination, the radioactive material cannot by definition be spread, but it is still measurable.) Volume contaminationVolumes of air, water, waste, or earth may contain radioactive contaminants. Volumetric contamination is expressed in units of radioactivity per unit volume (such as Bq/m3, or becquerels per cubic metre). The level of contamination may be determined by measuring the radiation emitted by the contaminant. In the case of a known radioisotope, it may be possible to accurately determine the activity simply from a dose rate measurement with a radiation meter. Spectral analysis of the radiation can also yield accurate estimates. In cases where the contaminant emits low-energy radiation, however, it may be difficult to determine its activity. HazardsIn practice there is no such thing as zero radioactivity. Not only is the entire world constantly bombard by cosmic rays, but every living creature on earth contains significant quantities of Carbon-14and most (including humans) contain significant quantities of Potassium-40. These tiny levels of radiation are not any more harmful than sunlight. But just as excessive quantities of sunlight can be dangerous, so too can excessive levels of radiation. Low level contaminationThe hazards to people and the environment from radioactive contamination depend on the nature of the radioactive contaminant, the level of contamination, and the extent of the spread of contamination. Low levels of radioactive contamination pose little risk , but can still be detected by radiation instrumentation. In the case of low-level contamination by isotopes with a short half-life, the best course of action may be to simply allow the material to naturally decay. Longer-lived isotopes should be cleaned up and properly disposed of. Image:Atmospheric radiation to human.jpg High levels of contaminationHigh levels of contamination may pose major risks to people and the environment. People can be exposed to potentially lethal radiation levels, both externally and internally, from the spread of contamination following an accident(or a deliberate detonation) involving large quantities of radioactive material. The biological effects of external exposureto radioactive contamination are generally the same as those from an external radiation source not involving radioactive materials, such as x-ray machines, and are dependent on the absorbed dose. Biological effectsThe biological effects of internally deposited radionuclides depend greatly on the activity and the biodistribution and removal rates of the radioisotope, which in turn depends on its chemical form. The biological effects may also depend on the chemical toxicityof the deposited material, independent of its radioactivity. Some radioisotopes may be generally distributed throughout the body and rapidly removed, as is the case with tritiated water. Some radioisotopes may target specific organs and have much lower removal rates. For instance, the thyroidgland takes up a large percentage of any iodine that enters the body. If large quantities of radioactive iodine are inhaled or ingested, the thyroid may be impaired or destroyed, while other tissues are affected to a lesser extent. Radioactive iodine is a common fission product; it was a major component of the radiation released from the Chernobyl disaster, leading to many cases of pediatric thyroid cancerand hypothyroidism. On the other hand, radioactive iodine is used in the diagnosis and treatment of many diseases of the thyroid precisely because of the thyroid's selective uptake of iodine. Means of contaminationRadioactive contamination can enter the body through ingestion, inhalation, absorption, or injection. For this reason, it is important to use personal protective equipmentwhen working with radioactive materials. Radioactive contamination may also be ingested as the result of eating contaminated plants and animals or drinking contaminated water or milk from exposed animals. Following a major contamination incident, all potential pathways of internal exposure should be considered. Decontaminationof external contamination is often as simple as removing contaminated clothing and cleaning contaminated skin. Internal decontamination can be much more difficult, depending on the radionuclide in question. See also
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