Radioactive contamination

The radiation warning symbol (trefoil).

Periodic table with elements colored according to the half-life of their most stable isotope.

  Elements which contain at least one stable isotope.

  Radioactive elements: the most stable isotope is very long-lived, with half-live of over four million years.

  Radioactive elements: the most stable isotope has half-life between 800 and 34.000 years.

  Radioactive elements: the most stable isotope has half-life between one day and 103 years.

  Highly radioactive elements: the most stable isotope has half-life between several minutes and one day.

  Extremely radioactive elements: the most stable isotope has half-life less than several minutes. Very little is known about these elements due to their extreme instability and radioactivity.

Radioactive contamination, also called radiological contamination, is radioactive substances on surfaces, or within solids, liquids or gases (including the human body), where their presence is unintended or undesirable, or the process giving rise to their presence in such places.^[1] Also used less formally to refer to a quantity, namely the activity on a surface (or on a unit area of a surface).

As with other contamination, radioactive contamination refers only to the presence of the unintended or undesired radioactivity, and gives no indication of the magnitude of hazard involved.

Sources of contamination

Radioactive contamination is typically the result of a spill or accident during the production or use of radionuclides (radioisotopes), an unstable nucleus which has excessive energy. Less typically, nuclear fallout is the distribution of radioactive contamination by a nuclear explosion. The amount of radioactive material released in an accident is called the source term.

Contamination may occur from radioactive gases, liquids or particles. For example, if a radionuclide used in nuclear medicine is spilled (accidentally or, as in the case of the Goiânia incident, through ignorance), 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 xenon in nuclear fuel reprocessing. In cases that radioactive material cannot be contained, it may be diluted to safe concentrations. For a discussion of environmental contamination by alpha emitters please see actinides in the environment.

Containment is what differentiates radioactive material from radioactive contamination. Contamination does not include residual radioactive material remaining at a site after the completion of decommissioning. Therefore, radioactive material in sealed and designated containers is not properly referred to as contamination, although the units of measurement might be the same.

Radiation monitoring

Radiation monitoring involves the measurement of radiation dose or radionuclide contamination for reasons related to the assessment or control of exposure to radiation or radioactive substances, and the interpretation of the results. The methodological and technical details of the design and operation of environmental radiation monitoring programmes and systems for different radionuclides, environmental media and types of facility are given in IAEA Safety Standards Series No. RS–G-1.8 ^[2] and in IAEA Safety Reports Series No. 64.^[3]

Measurement

Radioactive 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 contamination

Surface contamination is usually expressed in units of radioactivity per unit of area. For SI, this is becquerels per square meter (or Bq/m²). Other units such as picoCuries per 100 cm² or disintegrations per minute per square centimeter (1 dpm/cm² = 167 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.

Hazards

In the natural world, there is always radiation being emitted from radionuclides as they decay. Not only is the entire world constantly bombarded by cosmic rays, but practically every living thing on earth contains carbon-14 and tritium and most (including humans) contain some potassium-40. These tiny levels of radioactivity pose little danger because the natural radioisotopes are diluted amongst stable isotopes. All of these sources of ionizing radiation form the natural background radiation. When, however, radioactive isotopes are concentrated in a particular place outside of a planned containment, we call that concentrated area contaminated. If radioactive contamination is acute (highly concentrated enough to pose a risk of radiation exposure), then we call that location a "hot spot."

Many instances of contamination arise from particles that have become airborne. Prior to the deposition of radionuclides on a surface, the air is contaminated, which poses an inhalation hazard.

Low level contamination

The 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. If a survey or map is made of a contaminated area, random sampling locations may be labeled with their activity in bequerels or curies on contact. Low levels may be reported in counts per minute using a scintillation counter.

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, because even a very low level of radiation can be life-threatening when in long exposure to it.

Facilities and physical locations that are deemed to be contaminated may be cordoned off by a health physicist and labeled "Contaminated area." Persons coming near such an area would typically require anti-contamination clothing or anti-c's.

High level contamination

High 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 initiation) involving large quantities of radioactive material. The biological effects of external exposure to 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.

When radioactive contamination is being measured or mapped in situ, any location that appears to be a point source of radiation is likely to be heavily contaminated. A highly contaminated location is colloquially referred to as a "hot spot." On a map of a contaminated place, hot spots may be labeled with their "on contact" dose rate in mSv/hr. In a contaminated facility, hot spots may be marked with a sign, shielded with bags of lead shot, or cordoned off with warning tape containing the radioactive trefoil symbol in magenta on a yellow background.

Airborne contamination

The air can be contaminated with radioactive isotopes. Airborne radioisotopes pose a serious hazard to people who breathe the contaminated air. Respirators and air filters can help mitigate these dangers. Meters that sample the air may use a fan to draw in a metered amount of air across a special HEPA filter. The activity on the HEPA filter represents the contamination in the air; therefore, the HEPA filter is checked for contamination using the same meters used to test for surface contamination.

Biological effects

See also: Radiation poisoning

The biological effects of internally deposited radionuclides depend greatly on the activity, the biodistribution, and the removal rates of the radionuclide, which in turn depends on its chemical form, the particle size, and route of entry. Effects may also depend on the chemical toxicity of the deposited material, independent of its radioactivity. Some radionuclides may be generally distributed throughout the body and rapidly removed, as is the case with tritiated water.

Some organs concentrate certain elements and hence radionuclide variants of those elements. This action may lead to much lower removal rates. For instance, the thyroid gland takes up a large percentage of any iodine that enters the body. Large quantities of inhaled or ingested radioactive iodine may impair or destroy the thyroid, while other tissues are affected to a lesser extent. Radioactive iodine-131 is a common fission product; it was a major component of the radiation released from the Chernobyl disaster, leading to nine fatal cases of pediatric thyroid cancer and 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 contamination

Radioactive contamination can enter the body through ingestion, inhalation, absorption, or injection. For this reason, it is important to use personal protective equipment when 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.

In the media

• The Atom Strikes! (1945) — official US War Department film documenting damage to Hiroshima and Nagasaki.
• Gembaku no ko (1952) — documentary showing a Japanese school teacher who visits her hometown of Hiroshima 6 years after the bombing to find the horrors of radiation.
• The War Game (1965) - banned television docudrama about a Soviet nuclear attack on Britain, not shown on TV until 1985
• Hiroshima Nagasaki August 1945 (1970) — documentary of atomic bomb devastation.
• The Atomic Cafe (1982) — documentary combines stock US government footage of nuclear testing along with propaganda films shown in public schools in the 1940s and 1950s about how citizens should respond to atomic attacks.
• The Day After (1983) — TV docudrama about the effects of a nuclear holocaust on the small-town residents in eastern Kansas.
• Radio Bikini (1988) — documentary film about Bikini Atoll atomic tests. Gruesome details and pictures of joking sailors being irradiated, and interview with an injured (irradiated) sailor.
• Hiroshima: Out of the Ashes (1990) — TV history and graphic depictions of the horror of nuclear war.
• K-19: Doomsday Submarine (2002) — TV documentary about Russia's disastrous first nuclear submarine.
• K-19: The Widowmaker (2002) — docudrama about the first of many disasters that befell the Soviet submarine K-19
• The Last Atomic Bomb (2006) — documentary about the fate of the survivors of Nagasaki 1945.
• White Light/Black Rain: The Destruction of Hiroshima and Nagasaki (2007) — HBO documentary showing how many teenage Japanese are ignorant of what happened in 1945. Also includes some American atomic veterans.

Also see Criticality accident for six more films about radioactive issues.

• List of films about nuclear issues

See also

• Background radiation
• Bikini Atoll
• Chernobyl disaster
• Criticality accident
• Exotic pollution
• Goiânia accident
• Ionizing Radiation (includes physicists' units of radiation exposure)
• Lists of nuclear disasters and radioactive incidents
• Low-background steel
• Nuclear and radiation accidents
• Nuclear debate (disambiguation)
• Nuclear power
• Radiation biology
• Radiation exposure (disambiguation)
• Radiation poisoning
• Radioactive waste
• Radiophobia
• Relative Biological Effectiveness
• Rongelap Atoll
• Soviet submarine K-19

References

1. ^ International Atomic Energy Agency (2007). IAEA Safety Glossary: Terminology Used in Nuclear Safety and Radiation Protection. Vienna: IAEA. ISBN 92-0-100707-8. http://www-pub.iaea.org/MTCD/publications/PDF/Pub1290_web.pdf. 
2. ^ International Atomic Energy Agency (2005). Environmental and Source Monitoring for Purposes of Radiation Protection, IAEA Safety Standards Series No. RS–G-1.8. Vienna: IAEA. http://www-pub.iaea.org/MTCD/publications/PDF/Pub1216_web.pdf. 
3. ^ International Atomic Energy Agency (2010). Programmes and Systems for Source and Environmental Radiation Monitoring. Safety Reports Series No. 64.. Vienna: IAEA. pp. 234. ISBN 978-92-0-112409-8. http://www-pub.iaea.org/mtcd/publications/PubDetails.asp?pubId=8242. 

External links

• Alliance for Nuclear Responsibility