Ionizing radiation is used in a wide variety of fields such as medicine, nuclear power, research, manufacturing, construction, and many other areas, but presents a health hazard if proper measures against undesired exposure are not followed. Alpha () radiation consists of a fast-moving helium-4 (4 He) nucleus and is stopped by a sheet of paper.
Beta () radiation, consisting of electrons, is halted by an aluminum plate. Gamma () radiation, consisting of energetic photons, is eventually absorbed as it penetrates a dense material.
They were employed mainly in research in the early days of particle physics, but remain an important education tool today. Ionizing radiation is categorized by the nature of the particles or electromagnetic waves that create the ionizing effect. These have different ionization mechanisms, and may be grouped as directly or indirectly ionizing.
Any charged particle with mass can ionize atoms directly by fundamental interaction through the Coulomb force if it carries sufficient kinetic energy. The first two ionizing sources to be recognized were given special names used today: Helium nuclei ejected from atomic nuclei are called alpha particles, and electrons usually ejected (but not always) at relativistic speeds, are called beta particles.
In the atmosphere such particles are often stopped by air molecules, and this produces short-lived charged ions, which soon decay to muons, a primary type of cosmic ray radiation that reaches the ground (and also penetrates it to some extent). Ions can also be produced in large amounts in particle accelerators.
Alpha particles are named after the first letter in the Greek alphabet, . If the ion gains electrons from its environment, the alpha particle can be written as a normal (electrically neutral) helium atom 4 2 He.
When they result from radioactive alpha decay they have low penetration depth. More powerful, long range 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 nuclear decay processes, and when encountered in space, are thus able to traverse the human body and dense shielding. Beta particles When something is said to have radioactive contamination, it often means that there are beta particles being emitted from its surface, detectable with a Geiger counter or other radiation detector.
When brought into proximity to the beta emitter, the detector will indicate a dramatic increase in radioactivity. When the detector probe is covered with a shield to block the beta rays, the indication will be reduced dramatically.
High-energy beta particles may produce X -rays known as bremsstrahlung (“braking radiation”) or secondary electrons (delta ray) as they pass through matter. In space, however, very high energy protons, helium nuclei, and HE 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. When a charged nucleus strikes a relatively slow-moving nucleus of an object in space, LET occurs and neutrons, alpha particles, low-energy protons, and other nuclei will be released by the collisions and contribute to the total absorbed dose of tissue.
Indirect ionizing radiation is electrically neutral and therefore does not interact strongly with matter. Photon radiation The total absorption coefficient of lead (atomic number 82) for gamma rays, plotted versus gamma energy, and the contributions by the three effects.
Definition boundary for lower-energy photons The lowest ionization energy of any element is 3.89 eV, for cesium. However, US Federal Communications Commission material defines ionizing radiation as that with a photon energy greater than 10 eV (equivalent to a far ultraviolet wavelength of 124 nanometers).
A good example is ultraviolet spectrum energy which begins at about 3.1 eV (400 nm) at close to the same energy level which can cause sunburn to unprotected skin, as a result of photoreactions in collagen and (in the UV-B range) also damage in DNA (for example, pyrimidine divers). Thus, the mid and lower ultraviolet electromagnetic spectrum is damaging to biological tissues as a result of electronic excitation in molecules which falls short of ionization, but produces similar non-thermal effects.
To some extent, visible light and also ultraviolet A (UVA) which is closest to visible energies, have been proven to result in formation of reactive oxygen species in skin, which cause indirect damage since these are electronically excited molecules which can inflict reactive damage, although they do not cause sunburn (erythema). 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 LET does occur. Whether elastic or inelastic scatter occurs is dependent on the speed of the neutron, whether fast or thermal or somewhere in between.
While not a favorable reaction, the 16 O (n, p) 16 N 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. Outside the nucleus, free neutrons are unstable and have a mean lifetime of 14 minutes, 42 seconds.
Ionized air glows blue around a beam of particulate ionizing radiation from a cyclotron Ionization of molecules can lead to hydrolysis (breaking chemical bonds), and formation of highly reactive free radicals. These free radicals may then react chemically with neighboring materials even after the original radiation has stopped.
Simple diatomic compounds with very negative enthalpy of formation, such as hydrogen fluoride will reform rapidly and spontaneously after ionization. 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.
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. The most common impact is stochastic induction of cancer with a latent period of years or decades after exposure.
The mechanism by which this occurs is well understood, but quantitative models predicting the level of risk remain controversial. Other stochastic effects of ionizing radiation are teratogenesis, cognitive decline, and heart disease.
The table below shows radiation and dose quantities in SI and non-SI units. The relationships of the ICP dose quantities are shown in the accompanying diagram.
Its usefulness must be balanced with its hazards, a compromise that has shifted over time. Natural sources include the sun, lightning and supernova explosions.
The remaining 20% results from exposure to man-made radiation sources, primarily from medical imaging. Average man-made exposure is much higher in developed countries, mostly due to CT scans and nuclear medicine.
The background rate for natural radiation varies considerably with location, being as low as 1.5 MTV/a (1.5 MTV per year) in some areas and over 100 MTV/an in others. The highest level of purely natural radiation recorded on the Earth's surface is 90 AGY/h (0.8 GY/a) on a Brazilian black beach composed of magazine.
The highest background radiation in an inhabited area is found in Ramsay, primarily due to naturally radioactive limestone used as a building material. Some 2000 of the most exposed residents receive an average radiation dose of 10 may per year, (1 rad /yr) ten times more than the ICP recommended limit for exposure to the public from artificial sources.
This unique case is over 200 times higher than the world average background radiation. Despite the high levels of background radiation that the residents of Ramsay receive there is no compelling evidence that they experience a greater health risk.
The ICP recommendations are conservative limits and may represent an over representation of the actual health risk. Generally radiation safety organization recommend the most conservative limits assuming it is best to err on the side of caution.
This level of caution is appropriate but should not be used to create fear about background radiation danger. This cosmic radiation consists of relativistic particles: positively charged nuclei (ions) from 1 protons (about 85% of it) to 26 amu iron nuclei and even beyond.
The energy of this radiation can far exceed that which humans can create, even in the largest particle accelerators (see ultra-high-energy cosmic ray). This radiation interacts in the atmosphere to create secondary radiation that rains down, including x -rays, muons, protons, antiprotons, alpha particles, ions, electrons, positrons, and neutrons.
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 UNCLEAR 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. 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.
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 banana equivalent dose).
Shielding : Air or skin can be sufficient to substantially attenuate alpha and beta radiation. Barriers of lead, concrete, or water are often used to give effective protection from more penetrating particles such as gamma rays and neutrons.
Some radioactive materials are stored or handled underwater or by remote control in rooms constructed of thick concrete or lined with lead. Some generally accepted thicknesses of attenuating material are 5 mm of aluminum for most beta particles, and 3 inches of lead for gamma radiation.
For man-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 hot cell (for radiation) or glove box (for contamination).
Radioactive isotopes for medical use, for example, are dispensed in closed handling facilities, usually glove boxes, while nuclear reactors operate within closed systems with multiple barriers that keep the radioactive materials contained. Workrooms, hot cells and glove boxes have slightly reduced air pressures to prevent escape of airborne material to the open environment.
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 (I) tablets, which blocks the uptake of radioactive iodine (one of the major radioisotope products of nuclear fission) into the human thyroid gland.
Occupationally exposed individuals are controlled within the regulatory framework of the country they work in, and in accordance with any local nuclear license constraints. The International Commission on Radiological Protection recommends limiting artificial irradiation.
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. The public also is exposed to radiation from consumer products, such as tobacco (polonium -210), combustible fuels (gas, coal, etc.
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 MTV (0.001 SV) of effective dose per year, not including medical and occupational exposures. 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 earth's magnetic field who would receive solar particles from solar proton events (SPE) and galactic cosmic rays from cosmic sources. These high-energy charged nuclei are blocked by Earth's magnetic field but pose a major health concern for astronauts traveling to the moon and to any distant location beyond the earth orbit.
Highly charged HE ions in particular are known to be extremely damaging, although protons make up the vast majority of galactic cosmic rays. Evidence indicates past SPE radiation levels that would have been lethal for unprotected astronauts.
Air travel Air travel exposes people on aircraft to increased radiation from space as compared to sea level, including cosmic rays and from solar flare events. Software programs such as Card, CAR, SIEVERT, PCA IRE are attempts to simulate exposure by aircrews and passengers.
The United States FAA requires airlines to provide flight crew with information about cosmic radiation, and an International Commission on Radiological Protection recommendation for the public is no more than 1 MTV per year. In addition, many airlines do not allow pregnant flight crew members, to comply with a European Directive.
Information originally based on Fundamentals of Aerospace Medicine published in 2008. Hazardous levels of ionizing radiation are signified by the trefoil sign on a yellow background.
The red ionizing radiation warning symbol (ISO 21482) was launched in 2007, and is intended for IDEA Category 1, 2 and 3 sources defined as dangerous sources capable of death or serious injury, including food radiators, teletherapy machines for cancer treatment and industrial radiography units. It will not be visible under normal use, only if someone attempts to disassemble the device.
The symbol will not be located on building access doors, transportation packages or containers. Contribution of High Charge and Energy (HE) Ions During Solar-Particle Event of September 29, 1989, Kim, Myung-Hee Y.; Wilson, John W.; Cucinotta, Francis A.; Simon sen, Lisa C.; At well, William; ADAV, Francis F.; Miller, Jack, NASA Johnson Space Center; Langley Research Center, May 1999.
“Questions and Answers about Biological Effects and Potential Hazards of Radiofrequency Electromagnetic Fields” (PDF) (4th ed.). Washington, D.C.: GET (Office of Engineering and Technology) Federal Communications Commission.
Mac Master University, Department of Medical Physics and Radiation Sciences. “Irradiation of skin with visible light induces reactive oxygen species and matrix-degrading enzymes”.
^ United Nations Scientific Committee on the Effects of Atomic Radiation (2000). “New public dose assessment from internal and external exposures in low- and elevated-level natural radiation areas of Ramsay, Iran”.
Proceedings of the 6th International Conference on High Levels of Natural Radiation and Radon Areas. “Principles of Radiation Therapy” Archived 2009-05-15 at the Payback Machine in Pander R, Wag man LD, Campuses A, Hopkins WE (Eds) Cancer Management: A Multidisciplinary Approach Archived 2013-10-04 at the Payback Machine.