Ionizing radiation
Ionizing radiation (US) (or ionising radiation [UK]), including nuclear radiation, consists of
Typical ionizing subatomic particles include
Ionizing radiation is not immediately detectable by human senses, so instruments such as Geiger counters are used to detect and measure it. However, very high energy particles can produce visible effects on both organic and inorganic matter (e.g. water lighting in Cherenkov radiation) or humans (e.g. acute radiation syndrome).[4]
Ionizing radiation is used in a wide variety of fields such as
Directly ionizing radiation
Ionizing radiation may be grouped as directly or indirectly ionizing.
Any charged particle with mass can ionize
Two of the first types of directly ionizing radiation to be discovered are
Natural
Alpha particles
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus. Alpha particle emissions are generally produced in the process of alpha decay.
Alpha particles are a strongly ionizing form of radiation, but when emitted by radioactive decay they have low penetration power and can be absorbed by a few centimeters of air, or by the top layer of human skin. More powerful alpha particles from ternary fission are three times as energetic, and penetrate proportionately farther in air. The helium nuclei that form 10–12% of cosmic rays, are also usually of much higher energy than those produced by radioactive decay and pose shielding problems in space. However, this type of radiation is significantly absorbed by the Earth's atmosphere, which is a radiation shield equivalent to about 10 meters of water.[7]
The alpha particle was named by Ernest Rutherford after the first letter in the Greek alphabet, α, when he ranked the known radioactive emissions in descending order of ionising effect in 1899. The symbol is α or α2+. Because they are identical to helium nuclei, they are also sometimes written as He2+
or 4
2He2+
indicating a Helium ion with a +2 charge (missing its two electrons). If the ion gains electrons from its environment, the alpha particle can be written as a normal (electrically neutral) helium atom 4
2He.
Beta particles
Beta particles are high-energy, high-speed
High-energy beta particles may produce X-rays known as
Positrons and other types of antimatter
The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. When a low-energy positron collides with a low-energy electron, annihilation occurs, resulting in their conversion into the energy of two or more gamma ray photons (see electron–positron annihilation). As positrons are positively charged particles they can directly ionize an atom through Coulomb interactions.
Positrons can be generated by
Charged nuclei
Charged nuclei are characteristic of galactic cosmic rays and solar particle events and except for alpha particles (charged helium nuclei) have no natural sources on earth. In space, however, very high energy protons, helium nuclei, and HZE ions can be initially stopped by relatively thin layers of shielding, clothes, or skin. However, the resulting interaction will generate secondary radiation and cause cascading biological effects. If just one atom of tissue is displaced by an energetic proton, for example, the collision will cause further interactions in the body. This is called "linear energy transfer" (LET), which utilizes elastic scattering.
LET can be visualized as a billiard ball hitting another in the manner of the
Indirectly ionizing radiation
Indirectly ionizing radiation is electrically neutral and does not interact strongly with matter, therefore the bulk of the ionization effects are due to secondary ionization.
Photon radiation
Even though photons are electrically neutral, they can ionize
Radiated photons are called gamma rays if they are produced by a nuclear reaction, subatomic particle decay, or radioactive decay within the nucleus. They are called x-rays if produced outside the nucleus. The generic term "photon" is used to describe both.[11][12][13]
X-rays normally have a lower energy than gamma rays, and an older convention was to define the boundary as a wavelength of 10−11 m (or a photon energy of 100 keV).
Photoelectric absorption is the dominant mechanism in organic materials for photon energies below 100 keV, typical of classical X-ray tube originated
Definition boundary for lower-energy photons
The lowest ionization energy of any element is 3.89 eV, for
Neutrons
Neutrons have a neutral electrical charge often misunderstood as zero electrical charge and thus often do not directly cause ionization in a single step or interaction with matter. However, fast neutrons will interact with the protons in hydrogen via linear energy transfer, energy that a particle transfers to the material it is moving through. This mechanism scatters the nuclei of the materials in the target area, causing direct ionization of the hydrogen atoms. When neutrons strike the hydrogen nuclei, proton radiation (fast protons) results. These protons are themselves ionizing because they are of high energy, are charged, and interact with the electrons in matter.
Neutrons that strike other nuclei besides hydrogen will transfer less energy to the other particle if linear energy transfer does occur. But, for many nuclei struck by neutrons, inelastic scattering occurs. Whether elastic or inelastic scatter occurs is dependent on the speed of the neutron, whether fast or thermal or somewhere in between. It is also dependent on the nuclei it strikes and its neutron cross section.
In inelastic scattering, neutrons are readily absorbed in a type of
16O (n,p) 16N (fast neutron capture possible with >11 MeV neutron)
16N → 16O + β− (Decay t1/2 = 7.13 s)
This high-energy β− further interacts rapidly with other nuclei, emitting high-energy γ via Bremsstrahlung
While not a favorable reaction, the 16O (n,p) 16N reaction is a major source of X-rays emitted from the cooling water of a pressurized water reactor and contributes enormously to the radiation generated by a water-cooled nuclear reactor while operating.
For the best shielding of neutrons, hydrocarbons that have an abundance of hydrogen are used.
In
Outside the nucleus, free neutrons are unstable and have a mean lifetime of 14 minutes, 42 seconds. Free neutrons decay by emission of an electron and an electron antineutrino to become a proton, a process known as beta decay:[20]
In the adjacent diagram, a neutron collides with a proton of the target material, and then becomes a fast recoil proton that ionizes in turn. At the end of its path, the neutron is captured by a nucleus in an (n,γ)-reaction that leads to the emission of a neutron capture photon. Such photons always have enough energy to qualify as ionizing radiation.
Physical effects
Nuclear effects
Neutron radiation, alpha radiation, and extremely energetic gamma (> ~20 MeV) can cause nuclear transmutation and induced radioactivity. The relevant mechanisms are neutron activation, alpha absorption, and photodisintegration. A large enough number of transmutations can change macroscopic properties and cause targets to become radioactive themselves, even after the original source is removed.
Chemical effects
Ionization of molecules can lead to
High-intensity ionizing radiation in air can produce a visible
Monatomic fluids, e.g. molten
Electrical effects
Ionization of materials temporarily increases their conductivity, potentially permitting damaging current levels. This is a particular hazard in semiconductor microelectronics employed in electronic equipment, with subsequent currents introducing operation errors or even permanently damaging the devices. Devices intended for high radiation environments such as the nuclear industry and extra-atmospheric (space) applications may be made radiation hard to resist such effects through design, material selection, and fabrication methods.
Proton radiation found in space can also cause
Health effects
Most adverse health effects of exposure to ionizing radiation may be grouped in two general categories:
- deterministic effects (harmful tissue reactions) due in large part to killing or malfunction of cells following high doses from radiation burns.
- stochastic effects, i.e., cancer and heritable effects involving either cancer development in exposed individuals owing to mutation of somatic cells or heritable disease in their offspring owing to mutation of reproductive (germ) cells.[21]
The most common impact is stochastic induction of cancer with a latent period of years or decades after exposure. For example, ionizing radiation is one cause of chronic myelogenous leukemia,[22][23][24] although most people with CML have not been exposed to radiation.[23][24] The mechanism by which this occurs is well understood, but quantitative models predicting the level of risk remain controversial.[citation needed]
The most widely accepted model, the
Although
Measurement of radiation
The table below shows radiation and dose quantities in SI and non-SI units.
Quantity | Detector | CGS units
|
SI units
|
Other units |
---|---|---|---|---|
Disintegration rate | curie | becquerel | ||
Particle flux | Geiger counter, proportional counter, scintillator | counts/cm2 · second | counts/metre2 · second | counts per minute, particles per cm2 per second |
Energy fluence
|
thermoluminescent dosimeter, film badge dosimeter | MeV/cm2 | joule/metre2 | |
Beam energy | proportional counter | electronvolt | joule | |
Linear energy transfer | derived quantity | MeV/cm | Joule/metre | keV/μm |
Kerma | ionization chamber, semiconductor detector, quartz fiber dosimeter, Kearny fallout meter | esu/cm3 | gray (joule/kg) | roentgen |
Absorbed dose | calorimeter | rad |
gray | rep |
Equivalent dose | derived quantity | rem |
sievert (joule/kg × WR) | |
Effective dose | derived quantity | rem |
sievert (joule/kg × WR × WT) | BRET |
Committed dose | derived quantity | rem |
sievert | banana equivalent dose |
Uses of radiation
Ionizing radiation has many industrial, military, and medical uses. Its usefulness must be balanced with its hazards, a compromise that has shifted over time. For example, at one time, assistants in shoe shops in the US used X-rays to check a child's shoe size, but this practice was halted when the risks of ionizing radiation were better understood.[27]
Neutron radiation is essential to the working of
Sources of radiation
Ionizing radiation is generated through nuclear reactions, nuclear decay, by very high temperature, or via acceleration of charged particles in electromagnetic fields. Natural sources include the sun, lightning and supernova explosions. Artificial sources include nuclear reactors, particle accelerators, and x-ray tubes.
The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) itemized types of human exposures.
Public exposure | ||
Natural Sources | Normal occurrences | Cosmic radiation
|
Terrestrial radiation
| ||
Enhanced sources | Metal mining and smelting
| |
Phosphate industry | ||
Coal mining and power production from coal | ||
Oil and gas drilling | ||
Rare earth and titanium dioxide industries
| ||
ceramics industries
| ||
Application of radium and thorium | ||
Other exposure situations | ||
Human-made sources | Peaceful purposes | Nuclear power production |
Transport of nuclear and radioactive material | ||
Application other than nuclear power | ||
Military purposes | Nuclear tests
| |
Residues in the environment. Nuclear fallout | ||
Historical situations | ||
Exposure from accidents | ||
Occupational radiation exposure | ||
Natural Sources | Cosmic ray exposures of aircrew and space crew | |
Exposures in extractive and processing industries | ||
Gas and oil extraction industries | ||
Radon exposure in workplaces other than mines | ||
Human-made sources | Peaceful purposes | Nuclear power industries |
Medical uses of radiation | ||
Industrial uses of radiation | ||
Miscellaneous uses | ||
Military purposes | Other exposed workers | |
Source UNSCEAR 2008 Annex B retrieved 2011-7-4 |
The International Commission on Radiological Protection manages the International System of Radiological Protection, which sets recommended limits for dose uptake.
Background radiation
Background radiation comes from both natural and human-made sources.
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
Natural background radiation comes from five primary sources: cosmic radiation, solar radiation, external terrestrial sources, radiation in the human body, and radon.
The background rate for natural radiation varies considerably with location, being as low as 1.5 mSv/a (1.5 mSv per year) in some areas and over 100 mSv/a in others. The highest level of purely natural radiation recorded on the Earth's surface is 90 µGy/h (0.8 Gy/a) on a Brazilian black beach composed of
Cosmic radiation
The Earth, and all living things on it, are constantly bombarded by radiation from outside our solar system. This cosmic radiation consists of relativistic particles: positively charged nuclei (ions) from 1
.The dose from cosmic radiation is largely from muons, neutrons, and electrons, with a dose rate that varies in different parts of the world and based largely on the geomagnetic field, altitude, and solar cycle. The cosmic-radiation dose rate on airplanes is so high that, according to the United Nations UNSCEAR 2000 Report (see links at bottom), airline flight crew workers receive more dose on average than any other worker, including those in nuclear power plants. Airline crews receive more cosmic rays if they routinely work flight routes that take them close to the North or South pole at high altitudes, where this type of radiation is maximal.
Cosmic rays also include high-energy gamma rays, which are far beyond the energies produced by solar or human sources.
External terrestrial sources
Most materials on Earth contain some radioactive atoms, even if in small quantities. Most of the dose received from these sources is from gamma-ray emitters in building materials, or rocks and soil when outside. The major radionuclides of concern for terrestrial radiation are isotopes of potassium, uranium, and thorium. Each of these sources has been decreasing in activity since the formation of the Earth.
Internal radiation sources
All earthly materials that are the building blocks of life contain a radioactive component. As humans, plants, and animals consume food, air, and water, an inventory of radioisotopes builds up within the organism (see
Radon
An important source of natural radiation is radon gas, which seeps continuously from bedrock but can, because of its high density, accumulate in poorly ventilated houses.
Radon-222 is a gas produced by the α-decay of radium-226. Both are a part of the natural uranium decay chain. Uranium is found in soil throughout the world in varying concentrations. Radon is the largest cause of lung cancer among non-smokers and the second-leading cause overall.[31]
Radiation exposure
There are three standard ways to limit exposure:
- Time: For people exposed to radiation in addition to natural background radiation, limiting or minimizing the exposure time will reduce the dose from the radiation source.
- Distance: Radiation intensity decreases sharply with distance, according to an inverse-square law (in an absolute vacuum).[32]
- Shielding: Air or skin can be sufficient to substantially attenuate alpha and beta radiation. Barriers of neutrons. Some radioactive materials are stored or handled underwater or by remote control in rooms constructed of thick concrete or lined with lead. There are special plastic shields that stop beta particles, and air will stop most alpha particles. The effectiveness of a material in shielding radiation is determined by its half-value thicknesses, the thickness of material that reduces the radiation by half. This value is a function of the material itself and of the type and energy of ionizing radiation. Some generally accepted thicknesses of attenuating material are 5 mm of aluminum for most beta particles, and 3 inches of lead for gamma radiation.
These can all be applied to natural and human-made sources. For human-made sources the use of Containment is a major tool in reducing dose uptake and is effectively a combination of shielding and isolation from the open environment. Radioactive materials are confined in the smallest possible space and kept out of the environment such as in a
In nuclear conflicts or civil nuclear releases civil defense measures can help reduce exposure of populations by reducing ingestion of isotopes and occupational exposure. One is the issue of potassium iodide (KI) tablets, which blocks the uptake of radioactive iodine (one of the major radioisotope products of nuclear fission) into the human thyroid gland.
Occupational exposure
Occupationally exposed individuals are controlled within the regulatory framework of the country they work in, and in accordance with any local nuclear licence constraints. These are usually based on the recommendations of the International Commission on Radiological Protection. The ICRP recommends limiting artificial irradiation. For occupational exposure, the limit is 50 mSv in a single year with a maximum of 100 mSv in a consecutive five-year period.[25]
The radiation exposure of these individuals is carefully monitored with the use of dosimeters and other radiological protection instruments which will measure radioactive particulate concentrations, area gamma dose readings and radioactive contamination. A legal record of dose is kept.
Examples of activities where occupational exposure is a concern include:
- Airline crew (the most exposed population)
- Industrial radiography
- Medical radiology and nuclear medicine[33][34]
- Uranium mining
- nuclear fuel reprocessing plantworkers
- Research laboratories (government, university and private)
Some human-made radiation sources affect the body through direct radiation, known as
Public exposure
Medical procedures, such as diagnostic
Of lesser magnitude, members of the public are exposed to radiation from the nuclear fuel cycle, which includes the entire sequence from processing uranium to the disposal of the spent fuel. The effects of such exposure have not been reliably measured due to the extremely low doses involved. Opponents use a cancer per dose model to assert that such activities cause several hundred cases of cancer per year, an application of the widely accepted Linear no-threshold model (LNT).
The International Commission on Radiological Protection recommends limiting artificial irradiation to the public to an average of 1 mSv (0.001 Sv) of effective dose per year, not including medical and occupational exposures.[25]
In a nuclear war, gamma rays from both the initial weapon explosion and fallout would be the sources of radiation exposure.
Spaceflight
Massive particles are a concern for astronauts outside the
Air travel
Air travel exposes people on aircraft to increased radiation from space as compared to sea level, including
Radiation hazard warning signs
Hazardous levels of ionizing radiation are signified by the trefoil sign on a yellow background. These are usually posted at the boundary of a radiation controlled area or in any place where radiation levels are significantly above background due to human intervention.
The red ionizing radiation warning symbol (ISO 21482) was launched in 2007, and is intended for
-
Ionizing radiation hazard symbol
-
2007 ISOIAEA Category 1, 2 and 3 sources defined as dangerous sources capable of death or serious injury.[38]
See also
- European Committee on Radiation Risk
- International Commission on Radiological Protection – manages the International System of Radiological Protection
- Ionometer
- Irradiated mail
- National Council on Radiation Protection and Measurements – US national organisation
- Nuclear safety
- Nuclear semiotics
- Radiant energy
- Exposure (radiation)
- Radiation hormesis
- Radiation physics
- Radiation protection
- Radiation Protection Convention, 1960
- Radiation protection of patients
- Sievert
- Treatment of infections after accidental or hostile exposure to ionizing radiation
References
- ^ "Ionizing radiation, health effects and protective measures". World Health Organization. 29 April 2016. Archived from the original on 29 March 2020. Retrieved 22 January 2020.
- ISBN 978-0471109327. Archivedfrom the original on 2015-10-19.
- ISBN 978-0763743475. Archivedfrom the original on 2015-10-17.
- ^ "Ionizing Radiation - Health Effects | Occupational Safety and Health Administration". www.osha.gov. Retrieved 2022-06-23.
- PMID 22217743.
- ^ Herrera Ortiz AF, Fernández Beaujon LJ, García Villamizar SY, Fonseca López FF. Magnetic resonance versus computed tomography for the detection of retroperitoneal lymph node metastasis due to testicular cancer: A systematic literature review. European Journal of Radiology Open.2021;8:100372. https://doi.org/10.1016/j.ejro.2021.100372
- ^ One kg of water per cm squared is 10 meters of water Archived 2016-01-01 at the Wayback Machine
- ^ "Beta Decay". Lbl.gov. 9 August 2000. Archived from the original on 3 March 2016. Retrieved 10 April 2014.
- ^ Contribution of High Charge and Energy (HZE) Ions During Solar-Particle Event of September 29, 1989 Kim, Myung-Hee Y.; Wilson, John W.; Cucinotta, Francis A.; Simonsen, Lisa C.; Atwell, William; Badavi, Francis F.; Miller, Jack, NASA Johnson Space Center; Langley Research Center, May 1999.
- ^ European Centre of Technological Safety. "Interaction of Radiation with Matter" (PDF). Radiation Hazard. Archived from the original (PDF) on 12 May 2013. Retrieved 5 November 2012.
- ISBN 978-0-201-02116-5.
- ISBN 978-0-12-436603-9. Archivedfrom the original on 2021-04-16. Retrieved 2020-10-26.
- ISBN 978-3-540-25312-9.
- ^ Charles Hodgman, Ed. (1961). CRC Handbook of Chemistry and Physics, 44th Ed. USA: Chemical Rubber Co. p. 2850.
- ^ Robert F. Cleveland, Jr.; Jerry L. Ulcek (August 1999). "Questions and Answers about Biological Effects and Potential Hazards of Radiofrequency Electromagnetic Fields" (PDF) (4th ed.). Washington, D.C.: OET (Office of Engineering and Technology) Federal Communications Commission. Archived (PDF) from the original on 2011-10-20. Retrieved 2011-12-07.
- ^ Jim Clark (2000). "Ionisation Energy". Archived from the original on 2011-11-26. Retrieved 2011-12-07.
- ^ "Ionizing & Non-Ionizing Radiation". Radiation Protection. EPA. 2014-07-16. Archived from the original on 2015-02-12. Retrieved 2015-01-09.
- ^ "Fundamental Quantities and Units for Ionizing Radiation (ICRU Report 85)". Journal of the ICRU. 11 (1). 2011. Archived from the original on 2012-04-20.
- ^ Hao Peng. "Gas Filled Detectors" (PDF). Lecture notes for MED PHYS 4R06/6R03 – Radiation & Radioisotope Methodology. MacMaster University, Department of Medical Physics and Radiation Sciences. Archived from the original (PDF) on 2012-06-17.
- ^ W.-M. Yao; et al. (2007). "Particle Data Group Summary Data Table on Baryons" (PDF). J. Phys. G. 33 (1). Archived from the original (PDF) on 2011-09-10. Retrieved 2012-08-16.
- ^ ICRP 2007, paragraph 55.
- OCLC 740632205.
- ^ a b "Chronic myeloid leukemia (CML)". Leukemia & Lymphoma Society. 2015-02-26. Archived from the original on 2019-09-22. Retrieved 22 September 2019.
- ^ U.S. National Library of Medicine. Archivedfrom the original on 29 September 2019. Retrieved 22 September 2019.
- ^ a b c ICRP 2007.
- PMID 22318388.
- PMID 15408494.
- ^ United Nations Scientific Committee on the Effects of Atomic Radiation (2000). "Annex B". Sources and Effects of Ionizing Radiation. Vol. 1. United Nations. p. 121. Archived from the original on 4 August 2012. Retrieved 11 November 2012.
- ISSN 1569-4860.
- .
- ^ "Health Risks". Radon. EPA. Archived from the original on 2008-10-20. Retrieved 2012-03-05.
- ^ Camphausen KA, Lawrence RC. "Principles of Radiation Therapy" Archived 2009-05-15 at the Wayback Machine in Pazdur R, Wagman LD, Camphausen KA, Hoskins WJ (Eds) Cancer Management: A Multidisciplinary Approach Archived 2013-10-04 at the Wayback Machine. 11 ed. 2008.
- S2CID 71757795.
- PMID 10524506.
- ^ "Superflares could kill unprotected astronauts". New Scientist. 21 March 2005. Archived from the original on 27 March 2015.
- ^ "Effective Dose Rate". NAIRAS (Nowcast of Atmospheric Ionizing Radiation System). Archived from the original on 2016-03-05.
- ^ ISBN 9780781774666. Archivedfrom the original on 2020-08-03. Retrieved 2015-06-27 – via Google Books.
- ^ a b "New Symbol Launched to Warn Public About Radiation Dangers". International Atomic Energy Agency. February 15, 2007. Archived from the original on 2007-02-17.
Literature
- ICRP (2007). The 2007 Recommendations of the International Commission on Radiological Protection (Annals of the ICRP). ICRP publication 103. Vol. 37:2–4. ISBN 978-0-7020-3048-2. Archived from the originalon 16 November 2012. Retrieved 17 May 2012.
External links
- The Nuclear Regulatory Commission regulates most commercial radiation sources and non-medical exposures in the US:
- NLM Hazardous Substances Databank – Ionizing Radiation
- United Nations Scientific Committee on the Effects of Atomic Radiation 2000 Report Volume 1: Sources, Volume 2: Effects
- Beginners Guide to Ionising Radiation Measurement
- Mike Hanley. "XrayRisk.com : Radiation Risk Calculator. Calculate Radiation Dose and Cancer Risk". (from CT scans and xrays).
- Free Radiation Safety Course Archived 2018-04-16 at the Wayback Machine
- Health Physics Society Public Education Website
- Oak Ridge Reservation Basic Radiation Facts