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Gamma ray

Gamma rays are an energetic form of electromagnetic radiation Electromagnetic radiation

Electromagnetic radiation is generally described as a self-propagating wave [i] in space with electric [i] ... 

 produced by radioactive decay Radioactive decay

Radioactive decay is the set of various processes by which unstable atomic nuclei [i] ... 

 or other nuclear or subatomic processes such as electron-positron annihilation Electron-positron annihilation

Electron-positron annihilation occurs when an electron [i] and a positron [i] collide. ... 

.

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Encyclopedia

Gamma rays are an energetic form of electromagnetic radiation Electromagnetic radiation

Electromagnetic radiation is generally described as a self-propagating wave [i] in space with electric [i] ... 

 produced by radioactive decay Radioactive decay

Radioactive decay is the set of various processes by which unstable atomic nuclei [i] ... 

 or other nuclear or subatomic processes such as electron-positron annihilation Electron-positron annihilation

Electron-positron annihilation occurs when an electron [i] and a positron [i] collide. ... 

.

Explanation


Gamma rays form the highest-energy end of the electromagnetic spectrum Electromagnetic spectrum

The electromagnetic spectrum is the range of all possible electromagnetic radiation [i]. ... 

. They are often defined to begin at an energy Energy

In general, the concept [i] of energy refers to "the potential for causing changes." The word is used in ... 

 of 10 keV, corresponding to a minimum frequency of 2.42 EHz, or a maximum wavelength of 124 pm Metre

The metre, or meter , is a measure of length [i]. ... 

, although electromagnetic radiation from around 10 keV to several hundred keV is also referred to as hard X-ray X-ray

X-rays are a form of electromagnetic radiation [i] with a wavelength [i] in the range of 10 to 0.01 nanometre [i] ... 

s. It is important to note that there is no physical difference between gamma rays and X-rays of the same energy — they are two names for the same electromagnetic radiation, just as sunlight Sunlight

Sunlight in the broad sense is the total spectrum [i] of electromagnetic radiation [i] give ... 

 and moonlight are two names for visible light Light

Light is electromagnetic radiation [i] with a wavelength [i] that is visible to the eye [i] or, in a technical [i] ... 

. Rather, gamma rays are distinguished from X-rays by their origin. Gamma ray is a term for high-energy electromagnetic radiation produced by nuclear transitions, while X-ray is a term for high-energy electromagnetic radiation produced by energy transitions due to accelerating electrons. Because it is possible for some electron transitions to be of higher energy than some nuclear transitions, there is an overlap between what we call low energy gamma rays and high energy X-rays.

Gamma rays are a form of ionizing radiation Ionizing radiation

Ionizing radiation has many practical uses, but it is also dangerous to human health.... 

; they are more penetrating than either alpha Alpha particle

Alpha particles are a highly ionizing [i] form of particle radiation [i] which have low pene... 

 or beta Beta particle

[i]s emitted by certain types of [[radioactive]... 

 radiation , but less ionizing. For instance, a gamma ray will pass through 1 cm of aluminium Aluminium

Aluminium or aluminum is the chemical element in the periodic table that has the symbol Al ... 

, while an alpha particle will be stopped by even a single sheet of paper.

Gamma sources are used for a range of applications in both medicine Medicine

Medicine is the branch of health science [i] and the sector of public life concerned with maintaining or ... 

 and industry Industry

An industry is generally any grouping of business [i]es that share a common method of generating profit [i] ... 

. For further details see commonly used gamma emitting isotopes. High energy synchrotron radiation High energy X-rays

High Energy X-rays or HEX-rays [i] are very hard X-rays [i], with 80 keV [i] - 1000 keV [i] typically on ... 

 nowadays covers the lower part of the Gamma Ray spectrum from an artificial, tuneable source.

Shielding

Shielding for γ rays requires large amounts of mass. The material used for shielding takes into account that gamma rays are better absorbed by materials with high atomic number and high density. Also, the higher the energy of the gamma rays, the thicker the shielding required. Materials for shielding gamma rays are typically illustrated by the thickness required to reduce the intensity of the gamma rays by one half . For example, gamma rays that require 1 cm of lead Lead

Lead is a chemical element [i] in the periodic table [i] that has the symbol Pb and atomic number [i] ... 

 to reduce their intensity by 50% will also have their intensity reduced in half by 6 cm of concrete Concrete

In construction [i], concrete is a composite [i] building material made from the comb ... 

 or 9 cm of packed dirt.

Interaction with matter




When a gamma ray passes through matter, the probability for absorption in a thin layer is proportional to the thickness of that layer. This leads to an exponential decrease of intensity with thickness:

Here, μ = n×σ is the absorption coefficient, measured in cm-1, n the number of atoms per cm3 in the material, σ the absorption cross section in cm2 and d the thickness of material in cm.

In passing through matter, gamma radiation ionizes via three main processes: the photoelectric effect Photoelectric effect

The photoelectric effect is the emission of electron [i]s from matter upon the absorption of electromagnetic radiation [i]... 

, Compton scattering Compton scattering

In physics [i], Compton scattering or the Compton effect, is the decrease in energy [i] of an X-ray [i] ... 

, and pair production.

  • Photoelectric Effect: This describes the case in which a gamma photon interacts with and transfers its energy to an atomic electron, ejecting that electron from the atom. The kinetic energy of the resulting photoelectron is equal to the energy of the incident gamma photon minus the binding energy of the electron. The photoelectric effect is the dominant energy transfer mechanism for x-ray and gamma ray photons with energies below 50 keV , but it is much less important at higher energies.


  • Compton Scattering: This is an interaction in which an incident gamma photon loses enough energy to an atomic electron to cause its ejection, with the remainder of the original photon's energy being emitted as a new, lower energy gamma photon with an emission direction different from that of the incident gamma photon. The probability of Compton scatter decreases with increasing photon energy. Compton scattering is thought to be the principal absorption mechanism for gamma rays in the intermediate energy range 100 keV to 10 MeV , an energy spectrum which includes most gamma radiation present in a nuclear explosion. Compton scattering is relatively independent of the atomic number of the absorbing material.


  • Pair Production: By interaction via the Coulomb force, in the vicinity of the nucleus, the energy of the incident photon is spontaneously converted into the mass of an electron-positron pair. A positron Positron

    The positron is the antiparticle [i] or the antimatter [i] counterpart of the electron [i]. ... 

     is the anti-matter equivalent of an electron; it has the same mass as an electron, but it has a positive charge equal in strength to the negative charge of an electron. Energy in excess of the equivalent rest mass of the two particles appears as the kinetic energy of the pair and the recoil nucleus. The positron has a very short lifetime . At the end of its range, it combines with a free electron. The entire mass of these two particles is then converted into two gamma photons of 0.51 MeV energy each.


The secondary electrons produced in any of these three processes frequently have enough energy to produce many ionizations up to the end of range.

The exponential absorption described above holds, strictly speaking, only for a narrow beam of gamma rays. If a wide beam of gamma rays passes through a thick slab of concrete, the scattering in from the sides reduces the absorption.

Gamma rays are often produced alongside other forms of radiation such as alpha or beta. When a nucleus emits an α or β particle, the daughter nucleus is sometimes left in an excited state. It can then jump down to a lower level by emitting a gamma ray in much the same way that an atomic electron can jump to a lower level by emitting visible light or ultraviolet Ultraviolet

Ultraviolet light is electromagnetic radiation [i] with a wavelength [i] shorter than that of visible l ... 

 radiation.


Gamma rays, x-rays, visible light Light

Light is electromagnetic radiation [i] with a wavelength [i] that is visible to the eye [i] or, in a technical [i] ... 

, and UV rays are all forms of electromagnetic radiation Electromagnetic radiation

Electromagnetic radiation is generally described as a self-propagating wave [i] in space with electric [i] ... 

. The only difference is the frequency Frequency

[i] of the number of times that a repeated event occurs per unit of [[time]... 

 and hence the energy Energy

In general, the concept [i] of energy refers to "the potential for causing changes." The word is used in ... 

 of the photons Photon

In modern physics [i], the photon is the elementary particle [i] responsible for electromagnetic phenomena [i] ... 

. Gamma rays are the most energetic.
An example of gamma ray production follows.

First 60Co Cobalt

Cobalt is a hard, lustrous, silver-gray metal [i], a chemical element [i]. ... 

 decays to excited 60Ni Nickel

Nickel is a metallic chemical element [i] in the periodic table [i] that has the symbol Ni and atomic number [i] ... 

 by beta decay Beta particle

[i]s emitted by certain types of [[radioactive]... 

:

Then the 60Ni drops down to the ground state by emitting two gamma rays in succession:

Gamma rays of 1.17 MeV and 1.33 MeV are produced.

Another example is the alpha decay of 241Am Americium

Americium is a synthetic element [i] in the periodic table [i] that has the symbol Am and atomic number [i] ... 

 to form 237Np; this alpha decay is accompanied by gamma emission. In some cases, the gamma emission spectrum for a nucleus is quite simple, while in other cases, such as with , the gamma emission spectrum is complex, revealing that a series of nuclear energy levels can exist. The fact that an alpha spectrum can have a series of different peaks with different energies reinforces the idea that several nuclear energy levels are possible.


Because a beta decay is accompanied by the emission of a neutrino Neutrino

The neutrino is an elementary particle [i]. ... 

 which also carries away energy, the beta spectrum does not have sharp lines, but instead it is a broad peak. Hence from beta decay alone it is not possible to probe the different energy levels found in the nucleus.

In optical Optics

Optics is a branch of physics [i] that describes the behavior and properties of light [i] and the inter ... 

 spectroscopy, it is well known that an entity which emits light can also absorb light at the same wavelength Wavelength

The wavelength is the distance between repeating units of a wave [i] pattern. ... 

 . For instance, a sodium flame can emit yellow light as well as absorb the yellow light from a sodium Sodium

Sodium is a chemical element [i] which has the symbol Na , atomic number 11, atomic mass 22.9898 g/mol, oxidation number [i] ... 

 vapour lamp. In the case of gamma rays, this can be seen in Mössbauer spectroscopy. Here, a correction for the energy lost by the recoil of the nucleus is made and the exact conditions for gamma ray absorption through resonance can be attained.

This is similar to the Frank Condon effects seen in optical spectroscopy.

Uses


The powerful nature of gamma rays have made them useful in the sterilization of medical equipment by killing bacteria Bacteria

Bacteria are a major group of living organism [i]s. ... 

. They are also used to kill bacteria and insects in foodstuffs, particularly meat, marshmallows, pie, eggs, and vegetables, to maintain freshness.

Due to their tissue penetrating property, gamma rays / X-rays have a wide variety of medical uses such as in CT Scans Computed tomography

Computed tomography , originally known as computed axial tomography and body section roentgen... 

 and radiation therapy Radiation therapy

Radiation therapy is the medical [i] use of ionizing radiation [i] as part of cancer [i] treatment [i] ... 

 . However, as a form of ionizing radiation Ionizing radiation

Ionizing radiation has many practical uses, but it is also dangerous to human health.... 

 they have the ability to effect molecular changes, particularly to DNA DNA

Deoxyribonucleic acid is a nucleic acid [i] that contains the genetic [i] instructions for t... 

, giving them the potential to cause cancer Cancer

Cancer is a class of disease [i]s or disorders characterized by uncontrolled division [i] ... 

.

Despite their cancer-causing properties, gamma rays are also used to treat some types of cancer Cancer

Cancer is a class of disease [i]s or disorders characterized by uncontrolled division [i] ... 

. In the procedure called gamma-knife surgery, multiple concentrated beams of gamma rays are directed on the growth in order to kill the cancerous cells. The beams are aimed from different angles to focus the radiation on the growth while minimising damage to the surrounding tissues.

Gamma rays are also used for diagnostic purposes in nuclear medicine Nuclear medicine

Nuclear medicine is a branch of medicine [i] and medical imaging [i] that uses unsealed radioactive [i] ... 

. Several gamma-emitting radioisotope Radionuclide

Atoms of chemical elements may have many isotopes with the same atomic numbers but different atomic weights /... 

s are used, one of which is technetium Technetium

|-
| Electron affinity [i] || -53 kJ/mol
... 

-99m. When administered to a patient, a gamma camera Gamma camera

[i]
[i]
... 

 can be used to form an image of the radioisotope's distribution by detecting the gamma radiation emitted. Such a technique can be employed to diagnose a wide range of conditions .

Gamma ray detectors are also starting to be used in Pakistan as part of the Container Security Initiative . These US$ United States dollar

For details of current paper money [i] and coins, see Federal Reserve Note [i] and United States coinage [i] ... 

5 million machines are advertised to scan 30 containers per hour. The objective of this technique is to pre-screen merchant ship containers before they enter U.S. ports.

In fiction

  • An accident involving gamma rays transformed the scientist Bruce Banner into the Incredible Hulk Hulk (comics)

    The Hulk is a fictional character [i], a superhero [i] appearing in Marvel Comics [i]. ... 

     in the Marvel comic Marvel Comics

    Marvel Comics is an American [i] comic book [i] line published by Marvel Entertainment [i] ... 

     of the same name. Many of the Hulk's villains and allies were also affected by gamma rays, and the standard in Marvel comics seems to be that the effects of gamma mutation on an individual depend on the subsconscious desires and psychological quirks of that individual .
  • In both Gundam Seed and Seed Destiny gamma ray technology is incorporated in the space cannon G.E.N.E.S.I.S.
  • In David Weber's David Weber

    David Mark Weber is an American science fiction [i] and fantasy [i] author [i] ... 

     Honorverse Honorverse

    The Honorverse is the semi-official name for the setting of a military science fiction [i] series of sto ... 

    , grasers are powerful gamma-radiation-powered energy weapons.
  • Metroids Metroid (species)

    Metroids are a fictional species [i] of alien [i] predators [i] from the video game series of the same name [i] ... 

    , creatures in the popular series of the same name, go through a large metamorphosis when exposed to gamma-radiation.
  • EVE Online EVE Online

    EVE Online is a persistent world multiplayer online game [i] ... 

    , a space-based mmorpg for the pc, has a group of weapons technology that uses various EM radiations as lasers, some of which are gamma lasers.

History


Gamma rays were discovered by the French chemist and physicist, Paul Ulrich Villard in 1900 while he was studying uranium Uranium

Uranium is a chemical element [i] in the periodic table [i] that has the symbol U and atomic number [i] ... 

. Working in the chemistry department of the École Normale École Normale Supérieure

The cole normale suprieure is a French [i] grande cole [i], whose main campus i ... 

 in rue d'Ulm, Paris Paris

native_name = Ville de Paris
|common_name = Paris
... 

 with self-constructed equipment, he found that the rays were not bent by a magnetic field Magnetic field

In physics [i], a magnetic field is that part of the electromagnetic field [i] that exists when there is ... 

.

For a time, it was assumed that gamma rays were particles. The fact that they were rays was demonstrated by the British Physicist, William Henry Bragg William Henry Bragg

Sir William Henry Bragg OM [i], MA [i], PhD [i], OKW [i]... 

 in 1910 when he showed that the rays ionized gas in a similar way to X-rays.

In 1914, Ernest Rutherford Ernest Rutherford

Ernest Rutherford, 1st Baron Rutherford of Nelson, OM [i], PC [i] ... 

 and Edward Andrade showed that gamma rays were a form of electromagnetic radiation by measuring their wavelengths using crystal diffraction X-ray crystallography

X-ray crystallography is a technique in crystallography [i] in which the pattern produced by the diffraction [i] ... 

. The wavelengths are similar to those of X-rays and are very short, in the range 10-11m to 10-14m. It was Rutherford Ernest Rutherford

Ernest Rutherford, 1st Baron Rutherford of Nelson, OM [i], PC [i] ... 

 who coined the name 'gamma rays', after naming 'alpha' and 'beta' rays; the natures of the different rays were unknown at that time.

Gamma-ray astronomy did not develop until it was possible to get our detectors above all or most of the atmosphere, using balloons or spacecraft. The first gamma-ray telescope, carried into orbit on the Explorer XI satellite in 1961, picked up fewer than 100 cosmic gamma-ray photons.
Perhaps the most spectacular discovery in gamma-ray astronomy came in the late 1960s and early 1970s. Detectors on board the Vela satellite series, originally military satellites, began to record bursts of these rays, not from Earth, but from deep space.

References

http://imagers.gsfc.nasa.gov/ems/gamma.html
http://www.sciencedaily.com/releases/2005/01/050128222047.htm
http://en.wikipedia.org/wiki/Radiation
http://www.rerf.or.jp/eigo/radefx/basickno/whatis.htm
http://www.meds.com/pdq/radio.html
http://www.cancer.gov/cancertopics/factsheet/Therapy/radiation
http://www.gcsechemistry.com/pwav46.htm
http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PHPAEN000008000011004954000001&idtype=cvips&gifs=yes
http://www.saic.com/products/security/relocatable-vacis/relocatable-vacis-faq.html
http://www.physics.isu.edu/radinf
http://www.astro.caltech.edu/~ejb/faq.html

See also

  • Gamma-ray astronomy
  • Gamma ray burst Gamma ray burst

    Gamma-ray bursts are the most luminous events known in the Universe [i] since the Big Bang [i]. ... 

    s
  • Radiation therapy Radiation therapy

    Radiation therapy is the medical [i] use of ionizing radiation [i] as part of cancer [i] treatment [i] ... 

  • High energy X-rays High energy X-rays

    High Energy X-rays or HEX-rays [i] are very hard X-rays [i], with 80 keV [i] - 1000 keV [i] typically on ... 

  • Food irradiation Food irradiation

    Food irradiation is the process of exposing food to ionizing radiation [i] in order to disinfest, sterilize [i] ... 

  • Types of rays:
    • a rays Alpha particle

      Alpha particles are a highly ionizing [i] form of particle radiation [i] which have low pene... 

    • ß rays Beta particle

      [i]s emitted by certain types of [[radioactive]... 

    • ? rays
    • n rays
    • d rays
    • e rays
  • X-rays X-ray

    X-rays are a form of electromagnetic radiation [i] with a wavelength [i] in the range of 10 to 0.01 nanometre [i] ...