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This figure illustrates the relative abilities of three different types of ionizing radiation to penetrate solid matter.

In physics, radiation describes any process in which energy travels through a medium or through space, ultimately to be absorbed by another body. Non-physicists often associate the word with ionizing radiation (e.g., as occurring in nuclear weapons, nuclear reactors, and radioactive substances), but it can also refer to electromagnetic radiation (i.e., radio waves, infrared light, visible light, ultraviolet light, and X-rays) which can also be ionizing radiation, to acoustic radiation, or to other more obscure processes. What makes it radiation is that the energy radiates (i.e., it travels outward in straight lines in all directions) from the source. This geometry naturally leads to a system of measurements and physical units that are equally applicable to all types of radiation. Some radiations can be hazardous.

Contents

Ionizing radiation

Some types of radiation have enough energy to ionize particles. Generally, this involves an electron being 'knocked out' of an atom's electron shells, which will give it a (positive) charge. This is often disruptive in biological systems, and can cause mutations and cancer.

These types of radiation generally occur in radioactive decay and waste.

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Alpha radiation

Alpha (α) decay is a method of decay in large nuclei. An alpha particle (helium nucleus, He2+), consisting of 2 neutrons and 2 protons, is emitted. Because of the particle's relatively high charge, it is heavily ionizing and will cause severe damage if ingested. However, due to the high mass of the particle, it has little energy and a low range; typically alpha particles can be stopped with a sheet of paper (or skin).

Beta(+/-) radiation

Beta-minus (β-) radiation consists of an energetic electron. It is less ionizing than alpha radiation, but more than gamma. The electrons can often be stopped with a few centimeters of metal. It occurs when a neutron decays into a proton in a nucleus, releasing the beta particle and an antineutrino.

Beta-plus (β+) radiation is the emission of positrons. Because these are antimatter particles, they annihilate any matter nearby, releasing gamma photons.

Gamma radiation

Gamma (γ) radiation consists of photons with a frequency of greater than 1019 Hz[1]. Gamma radiation occurs to rid the decaying nucleus of excess energy after it has emitted either alpha or beta radiation.

Non-ionizing radiation

Non-ionizing (or non-ionising) radiation, by contrast, refers to any type of radiation that does not carry enough energy per photon to ionize atoms or molecules. It especially refers to the lower energy forms of electromagnetic radiation (i.e., radio waves, microwaves, terahertz radiation, infrared light, and visible light). The effects of these forms of radiation on living tissue have only recently been studied. Instead of producing charged ions when passing through matter, the electromagnetic radiation has sufficient energy only for excitation, the movement of an electron to a higher energy state. Nevertheless, different biological effects are observed for different types of non-ionizing radiation.[1][2]

Neutron radiation

Neutron radiation is a kind of non-ionizing radiation that consists of free neutrons. These neutrons may be emitted during either spontaneous or induced nuclear fission, nuclear fusion processes, or from other nuclear reactions. It does not ionize atoms in the same way that charged particles such as protons and electrons do (exciting an electron), because neutrons have no charge. However, neutron interactions are largely ionizing, for example when neutron absorption results in gamma emission and the gamma subsequently removes an electron from an atom, or a nucleus recoiling from a neutron interaction is ionized and causes more traditional subsequent ionization in other atoms.

Electromagnetic radiation

Electromagnetic radiation (sometimes abbreviated EMR) takes the form of self-propagating waves in a vacuum or in matter. EM radiation has an electric and magnetic field component which oscillate in phase perpendicular to each other and to the direction of energy propagation. Electromagnetic radiation is classified into types according to the frequency of the wave, these types include (in order of increasing frequency): radio waves, microwaves, terahertz radiation, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays. Of these, radio waves have the longest wavelengths and Gamma rays have the shortest. A small window of frequencies, called visible spectrum or light, is sensed by the eye of various organisms, with variations of the limits of this narrow spectrum. EM radiation carries energy and momentum, which may be imparted when it interacts with matter.

The electromagnetic spectrum is the range of all possible electromagnetic radiation frequencies.[1] The electromagnetic spectrum (usually just spectrum) of an object is the characteristic distribution of electromagnetic radiation emitted by, or absorbed by, that particular object.

Light

Light, or visible light, is electromagnetic radiation of a wavelength that is visible to the human eye (about 400–700 nm), or up to 380–750 nm.[1] More broadly, physicists refer to light as electromagnetic radiation of all wavelengths, whether visible or not.

Thermal radiation

Thermal radiation is the process by which the surface of an object radiates its thermal energy in the form of electromagnetic waves. Infrared radiation from a common household radiator or electric heater is an example of thermal radiation, as is the light emitted by a glowing incandescent light bulb. Thermal radiation is generated when heat from the movement of charged particles within atoms is converted to electromagnetic radiation. The emitted wave frequency of the thermal radiation is a probability distribution depending only on temperature, and for a genuine black body is given by Planck’s law of radiation. Wien's law gives the most likely frequency of the emitted radiation, and the Stefan–Boltzmann law gives the heat intensity.

Black-body radiation

Black-body radiation is a common synonym for thermal radiation (see above). It is so-called because the ideal radiator of thermal energy would also be an ideal absorber of thermal energy: It would not reflect any light, and thus would appear to be absolutely black.

Discovery

Wilhelm Röntgen is credited with the discovery of X-Rays. When experimenting with a vacuum and a tube, he noticed a phosphorescence on a nearby plate of coated glass. While working with various isotopes of hydrogen, namely tritium, he found a drastic change in photonic emissions when measuring electrical charges in a vacuum. When he took pictures of the tritium, he found that the state of one solid piece would deteriorate quickly. In one month, he discovered the main properties of X-rays that we understand to this day. Henri Becquerel found that uranium salts caused fogging of an unexposed photographic plate, and Marie Curie discovered that only certain elements gave off these rays of energy. She named this behavior radioactivity.

In December 1899, Marie Curie and Pierre Curie discovered radium in pitchblende. This new element was two million times more radioactive than uranium, as described by Marie.

See also

External links

References

  1. ^ a b c d Kwan-Hoong Ng (20th – 22nd October 2003). "Non-Ionizing Radiations – Sources, Biological Effects, Emissions and Exposures". Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN ICNIR2003 Electromagnetic Fields and Our Health. http://www.who.int/peh-emf/meetings/archive/en/keynote3ng.pdf. 
  2. ^ John E. Moulder. "Static Electric and Magnetic Fields and Human Health". http://www.mcw.edu/gcrc/cop/static-fields-cancer-FAQ/toc.html. 

Simple English

Radiation is when energy moves through space away from a source (of radiation). Radiation is one of the best understood parts of physics. There are two broad classes of radiation: ionizing radiation which comes from radioactive materials and x-ray machines and non-ionizing radiation (usually electromagnetic radiation) which comes from other sources. Ionizing radiation, which carries a large energy in each particle, can change things that it hits, hurting people or animals or causing chemical changes. Non-ionizing radiation does not cause microscopic damage, but some types can cause chemical changes or make things hotter.

There are many different ways that energy can travel through space in this way. One way is in the form of shifting electrical and magnetic fields. This is why some common types of radiation are referred to as Electromagnetic radiation, also known as light. (A different way to think of electromagnetic radiation is as a stream of particles of energy called photons.) Another way that radiation can travel is in the form of tiny particles. These are pieces of atoms, like neutrons or protons (please see the article on atoms for more information). When radiation is made up of quickly moving particles (like pieces of atoms), it is referred to as particle radiation.

Many people are already familiar with different kinds of electromagnetic radiation/light. Scientists categorize this type of radiation based on its wavelength and frequency. Some kinds of electromagnetic radiation are:

  • Radio waves: This is the kind of electromagnetic radiation with the highest wavelength. Radio waves are used to send and receive communications.
  • Micro-waves: This is a special kind of radio wave that is used by a microwave oven to warm up food. Microwaves are also used for communications, as weapons, and to move electrical power from one place to another.
  • Radar waves: This is also a kind of radio wave that is used to spot airplanes in the sky and ships in the ocean. Radar is also used to see changes in weather.
  • Infrared waves: Most objects at room temperature let off infrared radiation. Although humans cannot see it, special types of cameras can pick up this kind of radiation. Usually, the hotter something is, the more infrared radiation it lets off, which means that these special cameras can see hot things, even behind walls.
  • Visible light: This is the radiation that we see all around us as what most people call "light."
  • Ultraviolet light: This is a type of radiation with more energy than visible light that gives people a sunburn. Ultraviolet light is also used to kill bacteria and to make some kinds of invisible ink visible.
  • X-rays and Gamma rays: These are extremely strong rays that are commonly used in medicine to photograph the interior of the body and treat cancer. However, in too large amounts, they are very dangerous to life.

Most people hear terms like radiation and immediately think of it as a bad or dangerous thing. It turns out that only certain types of radiation are ordinarily harmful to humans. For example, ultraviolet radiation can give people sunburn. X-rays and gamma rays can make a person sick, or even die if they are exposed to them for a very long time. Some types of particle radiation can also make people sick and lead to burns. Any type of radiation that causes changes in world like these is referred to as ionizing radiation. If radiation does not carry high enough levels of energy, though, then these changes will not happen when something is hit by the radiation. This is referred to as non-ionizing radiation, which is not as dangerous.

One can distinguish between various types of radiation by looking at the source of the radiation, its wavelength (if the radiation is electromagnetic), the amount of energy being carried, any particles involved, etc. Radioactive material is a physical material that emits radiation. Uranium and plutonium are examples of radioactive materials. The atoms they are made of tend to fall apart and give off different kinds of radiation, like gamma rays and lots of types of particle radiation.

Different Ionizing Radiations by type

  • Alpha radiation, a type of particle radiation made up of the nuclei of helium atoms.
  • Beta radiation, another type of particle radiation made up of high energy electrons or positrons.
  • Neutron radiation, yet another type of particle radiation made up of high energy neutrons.
  • Gamma radiation (Gamma rays), a type of radiation made up of high energy photons.
  • X-ray radiation (X-rays), a type of radiation also made up of photons but which typically contain less energy than gamma rays.

Different Non-Ionizing Radiations by type

Other pages

  • Background radiation, refers to ionizing radiation that is always around us. Many types of scientific tools will not work correctly if background radiation levels are not known. For example, a Geiger counter.
  • Cosmic microwave background radiation, 3K blackbody radiation that fills the Universe
  • Radiant energy, radiation emitted by a source into its environment.
  • Radiation damage - destructive effects on materials and devices
  • Radiation hormesis - dosage threshold damage theory (unproven)
  • Radiation poisoning - destructive effects on life forms
  • Radiation hardening - making devices resistant to failure in high radiation environments
  • Radioactive contamination
  • Radioactive decay


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