Difference between revisions 1875976 and 1901055 on enwikiversity

[[Image:Detectors summary 3.png|thumb|right|250px|This tree diagram shows the relationship between types and classification of most common particle detectors. Credit: [[commons:User:Wdcf|Wdcf]].]]
'''Radiation detectors''' provide a signal that is converted to an electric current. The device is designed so that the current provided is proportional to the characteristics of the incident radiation.

There are detectors that provide a change in substance as the signal and these may be automated to provide an electric current or quantified proportional to the amount of new substance.
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==Astronomy==
{{main|Draft:Astronomy/Keynote lecture}}
A detector in [[Radiation astronomy/Keynote lecture|radiation astronomy]] may need to be able to separate a collection of incoming radiation to obtain a clear set of signals for the radiation of interest. For example, a detector designed for [[red astronomy]] may need to be on the rocky-object surface of the [[Earth]] to separate X-rays and gamma-rays from red rays.

==Radiation==
{{main|Draft:Radiation/Keynote lecture}}
'''Def.''' an action or process of throwing or sending out a traveling ray in a line, beam, or stream of small cross section is called '''radiation'''.

Radiation may affect materials and devices in deleterious ways:
* By causing the materials to become radioactive (mainly by neutron activation, or in presence of high-energy gamma radiation by photodisintegration).
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==Planetary sciences==
{{main|Planets/Sciences|Planetary sciences}}
[[Image:Ash and Steam Plume, Soufriere Hills Volcano, Montserrat.jpg|thumb|right|2
050px|This oblique astronaut photograph from the International Space Station (ISS) captures a white-to-grey ash and steam plume extending westwards from the Soufriere Hills volcano. Credit: NASA Expedition 21 crew.]]
Oblique images such as the one at right are taken by astronauts looking out from the International Space Station (ISS) at an angle, rather than looking straight downward toward the [[Earth]] (a perspective called a nadir view), as is common with most remotely sensed data from satellites. An oblique view gives the scene a more three-dimension quality, and provides a look at the vertical structure of the volcanic plume. While much of the island is covered in green vegetation, grey deposits that include pyroclastic flows and volcanic mud-flows (lahars) are visible extending from the volcano toward the coastline. When compared to its extent in earlier views, the volcanic debris has filled in more of the eastern coastline. Urban areas are visible in the northern and western portions of the island; they are recognizable by linear street patterns and the presence of bright building rooftops. The silver-grey appearance of the Caribbean Sea surface is due to sun-glint, which is the mirror-like reflection of sunlight off the water surface back towards the hand-held camera on-board the ISS. The sun-glint highlights surface wave patterns around the island.
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==Theoretical radiation detectors==

'''Def.''' "a device that recovers information of interest contained in a modulated wave"<ref name=DetectorRadio>{{ cite book
|author=[[w:User:Light current|Light current]]
|title=Detector (radio)
|publisher=Wikimedia Foundation, Inc
|location=San Francisco, California
|date=May 15, 2013
|url=http://en.wikipedia.org/wiki/Detector_(radio)
|accessdate=2013-05-25 }}</ref> is called a '''detector'''.

'''Def.''' a "device capable of registering a specific substance or physical phenomenon"<ref name=DetectorWikt>{{ cite book
|author=[[wikt:User:Hekaheka|Hekaheka]]
|title=detector
|publisher=Wikimedia Foundation, Inc
|location=San Francisco, California
|date=18 July 2008
|url=http://en.wiktionary.org/wiki/detector
|accessdate=2012-06-19 }}</ref> is called a '''detector'''.

'''Def.''' "a device used to detect, track, and/or identify high-energy particles, such as those produced by nuclear decay, cosmic radiation, or reactions in a particle accelerator"<ref name=ParticleDetector>{{ cite book
|author=[[w:User:Justanother|Justanother]]
|title=Particle detector
|publisher=Wikimedia Foundation, Inc
|location=San Francisco, California
|date=25 January 2007
|url=http://en.wikipedia.org/wiki/Particle_detector
|accessdate=2012-06-19 }}</ref> is called a '''radiation detector'''.

'''Def.''' "a device or organ that detects certain external stimuli and responds in a distinctive manner"<ref name=SensorWikt>{{ cite book
|author=[[wikt:User:Pathoschild|Pathoschild]]
|title=sensor
|publisher=Wikimedia Foundation, Inc
|location=San Francisco, California
|date=27 December 2006
|url=http://en.wiktionary.org/wiki/sensor
|accessdate=2012-06-19 }}</ref> is called a '''sensor'''.

Humans have a multitude of senses. Sight (ophthalmoception), hearing (audioception), taste (gustaoception), smell (olfacoception or olfacception), and touch (tactioception) are the five traditionally recognized. While the ability to detect other stimuli beyond those governed by the traditional senses exists, including temperature (thermoception), kinesthetic sense (proprioception), pain (nociception), balance (equilibrioception), acceleration (kinest(contracted; show full)

Cadmium telluride (CdTe) doped with chlorine is used as a radiation detector for [X-rays], gamma rays, beta particles and alpha particles. CdTe can operate at room temperature allowing the construction of compact detectors for a wide variety of applications in nuclear spectroscopy.<ref name="Capper">{{cite book
|title= Properties of Narrow-Gap Cadmium-Based Compounds
| author = P. Capper
| publisher = INSPEC, IEE
| location= London, UK
| 
yeardate = 1994
| isbn=0-85296-880-9 }}</ref> The properties that make CdTe superior for the realization of high performance gamma- and x-ray detectors are high atomic number, large bandgap and high electron mobility ~1100&nbsp;cm<sup>2</sup>/V·s, which result in high intrinsic μτ (mobility-lifetime) product and therefore high degree of charge collection and excellent spectral resolution.

==Entities==
{{main|Radiation astronomy/Entities|Entities}}
'''Def.''' "the fraction of photoelectric events which end up in the photopeak of the measured energy spectrum"<ref name="Krawczynski">{{cite book
|author=Henric S. Krawczynski ; Ira Jung ; Jeremy S. Perkins ; Arnold Burger ; Michael Groza
|title=Thick CZT Detectors for Space-Borne X-ray Astronomy, In: ''Hard X-Ray and Gamma-Ray Detector Physics VI, 1''
|publisher=The International Society for Optical Engineering
|location=Denver, Colorado USA
|monthdate=October 21,⏎
|year=2004  2004
|volume=5540
|issue=
|pages=13
|url=http://arxiv.org/pdf/astro-ph/0410077
|arxiv=astro-ph/0410077
|bibcode=
|doi=10.1117/12.558912
(contracted; show full) sequence. Humans recognize a multitude of objects in images with little effort, despite the fact that the image of the objects may vary somewhat in different view points, in many different sizes / scale or even when they are translated or rotated. Objects can even be recognized when they are partially obstructed from view. This task is still a challenge for computer vision systems in general.

==Continua==
{{main|Radiation astronomy/Continua|Continua}}
[[Image:Continuous radiation source.jpg|thumb|right|2
050px|This is a xenon lamp which serves as a continuous light radiation source. Credit: Analytik Jena AG.]]
A '''xenon arc lamp''' is a specialized type of gas discharge lamp, an electric light that produces light by passing electricity through ionized xenon gas at high pressure. It produces a bright white light that closely mimics natural sunlight.

(contracted; show full)

==Absorptions==
{{main|Radiation astronomy/Absorptions|Absorptions}}
[[Image:Spectroscopy overview.svg|thumb|upright=2|center|300px|This is an overview of [[w:electromagnetic radiation|electromagnetic radiation]] absorption. Credit: .]]
[[Image:Sodium in atmosphere of exoplanet HD 209458.jpg|thumb|upright=2|
250px|An example of applying Absorption spectroscopy is the first direct detection and chemical analysis of the atmosphere of a planet outside our solar system in 2001. Sodium filters the alien star light of [[w:HD 209458|HD 209458]] as the hot Jupiter planet passes in front. The process and absorption spectrum are illustrated above. Credit: A. Feild, STScI and NASA website.]]
(contracted; show full)resent (green light in this example) are ''absorbed'' in order to excite the molecule. Other photons transmit unaffected and, if the radiation is in the visible region (400-700nm), the sample color is the complementary color of the absorbed light. By comparing the [[w:attenuation|attenuation]] of the transmitted light with the incident, an absorption spectrum can be obtained.
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==Bands==
{{main|Radiation astronomy/Bands|Bands}}
[[Image:Bandgap in semiconductor.svg|right|thumb|2
050px|Semiconductor [[w:Electronic band structure|band structure]] is diagrammed qualitatively. Credit: [[commons:User:Pieter Kuiper|Pieter Kuiper]].]]
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The main components of background noise in neutron detection are high-energy photons, which aren't easily eliminated by physical barriers.

'''Noise''' is a random fluctuation in an electrical signal, a characteristic of all [[w:electronics|electronic]] [[w:electrical circuit|circuits]].<ref name="noise">{{cite book
|author=C. D. Motchenbacher, J. A. Connelly
|title=Low-noise electronic system design
|publisher=Wiley Interscience
|
yeardate=1993
|isbn=
|doi= }}</ref> Noise generated by electronic devices varies greatly, as it can be produced by several different effects. [[w:Thermal noise|Thermal noise]] is unavoidable at non-zero temperature (see [[w:fluctuation-dissipation theorem|fluctuation-dissipation theorem]]), while other types depend mostly on device type (such as [[w:shot noise|shot noise]],<ref name="noise"/><ref name="shot">{{cite journal
|author=L. B. Kish, C. G. Granqvist
(contracted; show full)ansil]], [[w:varistor|varistor]], overvoltage [[w:crowbar (circuit)|crowbar]], or a range of other overvoltage protective devices can divert ([[w:shunt (electrical)|shunt]]) this transient current thereby minimizing voltage.<ref>Transient Protection, LearnEMC Online Tutorial. http://www.learnemc.com/tutorials/Transient_Protection/t-protect.html</ref>

==Meteors==
{{main|Radiation astronomy/Meteors|Meteors}}
[[Image:Big Meteor Explosion on Moon-19d7f8e05ad0515a229533edae7f1b19.jpeg|thumb|right|2
050px|The white spot on this image of the Earth side of the Moon is the impact site of a meteor from March 17, 2013. Credit: NASA.]]
[[Image:Hs-2009-23-crop.jpg|thumb|left|2050px|This is a [[w:Hubble Space Telescope|Hubble Space Telescope]] image taken on July 23, 2009, showing a blemish of about 5,000 miles long left by the [[w:2009 Jupiter impact event|2009 Jupiter impact]].<ref name="Overbye">{{cite book
|author=Dennis Overbye
|title=Hubble Takes Snapshot of Jupiter’s ‘Black Eye’
|url=http://www.nytimes.com/2009/07/25/science/space/25hubble.html?ref=science
|date=2009-07-24
|publisher=New York Times
|accessdate=2009-07-25 }}</ref> Credit: NASA, ESA, and H. Hammel (Space Science Institute, Boulder, Colo.), and the Jupiter Impact Team.]]
Usually, a meteor detector is designed for another form of radiation that the meteor may radiate.

In the image at right, a 0.3 m meteor has impacted a ''meteor detector'', in this case the [[Moon]], and created a scintillation event that in turn is detected by a photoelectronic detector system.

In the image at left, a meteor has impacted another detector, here [[Jupiter]], but instead of a scintillation event has created a lowering of albedo as detected by the photoelectronic system, the Hubble Space Telescope.
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==Cosmic rays==
{{main|Radiation astronomy/Cosmic rays|Cosmic rays}}
[[Image:Cloud chamber bionerd.jpg|thumb|right|2050px|Cloud chamber shows visible tracks from α-particles (short, thick) and β-particles (long, thin). Credit: Bionerd.]]
[[Image:Electronic nuclear stopping Al in Al.png|thumb|right|2050px|Diagram shows the electronic and nuclear stopping power for aluminum ions in aluminum. Credit: HPaul.]]
[[Image:Ion slowing.png|thumb|right|2050px|This is an illustration of the slowing down of a single ion in a solid material. Credit: Kai Nordlund.]]
[[Image:Bragg Curve for Alphas in Air.png|thumb|right|2050px|A Bragg curve of 5.49 MeV alpha particles in air is illustrated. Credit: Helmut Paul.]]
The basic set-up consists of 1600 water tanks ([[w:Cherenkov detector|water Cherenkov Detectors]], similar to the [[w:Haverah Park experiment|Haverah Park experiment]]) distributed over 3,000 square kilometres (1,200 sq mi), along with four atmospheric [[w:fluorescence|fluorescence]] detectors (similar to the [[w:High Resolution Fly's Eye Cosmic Ray Detector|High Resolution Fly's Eye]]) overseeing the surfa(contracted; show full)
|author=Samuel Ting, Manuel Aguilar-Benitez, Silvie Rosier, Roberto Battiston, Shih-Chang Lee, Stefan Schael, and Martin Pohl
|title=Alpha Magnetic Spectrometer - 02 (AMS-02)
|publisher=NASA
|location=Washington, DC USA
|
monthdate=April 13,⏎
|year=  2013
|url=http://www.nasa.gov/mission_pages/station/research/experiments/742.html
|accessdate=2013-05-17 }}</ref>

The second figure on the right shows the electronic and nuclear stopping power of aluminum single crystal for aluminum ions. These stopping powers are versus particle energy per nucleon. The maximum of the nuclear stopping curve typically occurs at energies of the order of 1 keV per nucleon.

The third figure at right illustrates the slowing down of a single ion in a solid material.

(contracted; show full)

“[D]etection approaches for neutrons fall into several major categories<ref name="Tsoul">{{cite book
| last = Tsoulfanidis
 | first = Nicholas
| title = Measurement and Detection of Radiation
| publisher = Taylor & Francis
| date = 1995
 (2nd Edition)
| location = Washington, D.C.
| pages =467–501
| url =
| doi =
| isbn = 1-56032-317-5 }}</ref>:

* Absorptive reactions with prompt reactions - Low energy neutrons are typically detected indirectly through absorption reactions. Typical absorber materials used have high [[w:Cross section (physics)|cross sections]] for absorption of neutrons and include [[w:Helium-3|Helium-3]], [[w:Lithium-6|Lithium-6]], [[w:Boron-10|Boron-10]], and [[w:Uranium-235|Uranium-235]]. Each of these reacts by emission of hig(contracted; show full)atoms in the detector, transferring energy to that nucleus and creating an ion, which is detected. Since the maximum transfer of energy occurs when the mass of the atom with which the neutron collides is comparable to the neutron mass, hydrogenous [materials with a high hydrogen content such as water or plastic] materials are often the preferred medium for such detectors.<ref name="Tsoul"/>

==Protons==
{{main|Radiation astronomy/Protons|Protons}}
[[Image:MER APXS PIA05113.jpg|thumb|right|2
050px|This is an image of the alpha particle X-ray spectrometer (APXS). Credit: NASA/JPL-Caltech.]]
[[Image:Stopping H in Al.png|thumb|right|2050px|The stopping power of aluminum for protons is plotted versus proton energy. Credit: H.Paul.]]
Some of the alpha particles are absorbed by the atomic nuclei. The [alpha,proton] process produces protons of a defined energy which are detected. Sodium, magnesium, silicon, aluminium and sulfur can be detected by this method. This method was only used in the Mars Pathfinder APXS.

At right, the second figure shows the '''stopping power''' of aluminum metal single crystal for protons.

"Choosing materials with the largest stopping powers enables thinner detectors to be produced with resulting benefits in radiation tolerance (which is a bulk effect) and lower leakage currents. Alternatively, choosing smaller stopping powers will increase scattering efficiency, which is a requirement for polarimetry, or say, the upper detection plane of a double Compton telescope."<ref name="Owens">{{cite journal
|author=Alan Owens, A. Peacock
|title=Compound semiconductor radiation detectors
|journal=Nuclear Instruments and Methods in Physical Research A
|month=September
|year=2004
|volume=531
|issue=1-2
|pages=18-37
|url=http://www.msri.org/people/staff/levy/files/ToPrint/owens-compound.pdf
|arxiv=
|bibcode=
|doi=10.1016/j.nima.2004.05.071
|pmid=
|accessdate=2013-05-24 }}</ref>
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==Electrons==
{{main|Radiation astronomy/Electrons|Electrons}}
[[Image:Galileo Energetic Particles Detector.jpg|thumb|right|2050px|This is an image of the Energetic Particles Detector (EPD) aboard the Galileo Orbiter. Credit: NASA.]]
The Energetic Particles Detector (EPD) aboard the [[w:Galileo (spacecraft)|Galileo Orbiter]] is designed to measure the numbers and energies of electrons whose energies exceed about 20 [[w:keV|keV]]. The EPD [can] also measure the direction of travel of electrons. The EPD [uses] silicon solid state detectors and a [[w:time-of-flight|time-of-flight]] detector system to measure changes in the energetic [(contracted; show full)m] LEMMS [uses] magnetic deflection to separate incoming electrons and ions. The 180 degree end [uses] absorbers in combination with the detectors to provide measurements of higher-energy electrons ... The LEMMS [provides] measurements of electrons from 15 keV to greater than 11 MeV ... in 32 rate channels."<ref name="Williams">{{cite book
|author=Donald J. Williams
|title=Energetic Particles Detector (EPD)
|publisher=NASA Goddard Space Flight Center
|location=Greenbelt, Maryland USA
|
monthdate=May 14,⏎
|year=  2012
|url=http://nssdc.gsfc.nasa.gov/nmc/experimentDisplay.do?id=1989-084B-06
|accessdate=2012-08-11 }}</ref>
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==Positrons==
{{main|Radiation astronomy/Positrons|Positrons}}
"In the first 18 months of operations, AMS-02 [image under Cherenkov detectors] recorded 6.8 million positron (an antimatter particle with the mass of an electron but a positive charge) and electron events produced from cosmic ray collisions with the interstellar medium in the energy range between 0.5 giga-electron volt (GeV) and 350 GeV. These events were used to determine the positron fraction, the ratio of positrons to the total number of electrons and positrons. Below 10 GeV, the positron fraction decreased with increasing energy, as expected. However, the positron fraction increased steadily from 10 GeV to 250 GeV. This increase, seen previously though less precisely by instruments such as the Payload for Matter/antimatter Exploration and Light-nuclei Astrophysics (PAMELA) and the Fermi Gamma-ray Space Telescope, conflicts with the predicted decrease of the positron fraction and indicates the existence of a currently unidentified source of positrons, such as pulsars or the annihilation of dark matter particles. Furthermore, researchers observed an unexpected decrease in slope from 20 GeV to 250 GeV. The measured positron to electron ratio is isotropic, the same in all directions."<ref name="Ting"/>

==Muons==
{{main|Radiation astronomy/Muons|Muons}}
[[Image:CMScollaborationPoster1.gif|thumb|2050px|right|The [[w:Compact Muon Solenoid|Compact Muon Solenoid]] (CMS) is an example of a large particle detector. Notice the person for scale. Credit: CERN.]]
"With γ ray energy 50 times higher than the muon energy and a probability of muon production by the γ's of about 1%, muon detectors can match the detection efficiency of a GeV satellite detector if their effective area is larger by 10<sup>4</sup>."<ref name="Halzen">{{cite journal
|author=Francis Halzen, Todor Stanev, Gaurang B. Yodh
|title=γ ray astronomy with muons
|journal=Physical Review D Particles, Fields, Gravitation, and Cosmology
|month=April 1,
|year=1997
|volume=55
|issue=7
|pages=4475-9
|url=http://prd.aps.org/abstract/PRD/v55/i7/p4475_1
|arxiv=astro-ph/9608201
|bibcode=1997PhRvD..55.4475H
|doi=10.1103/PhysRevD.55.4475
|pmid=
|accessdate=2013-01-18 }}</ref>
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==Neutrinos==
{{main|Radiation astronomy/Neutrinos|Neutrinos}}
[[Image:Sudbury neutrino observatory.png|thumb|right|2050px|The Sudbury Neutrino Observatory, a 12-meter sphere filled with heavy water surrounded by light detectors located 2000 meters below the ground in Sudbury, Ontario, Canada. Credit: NASA.]]
A '''neutrino detector''' is designed to study [[w:neutrino|neutrino]]s. Because neutrinos are only [[w:Weak interaction|weakly interacting]] with other particles of matter, neutrino detectors must be very large in order to detect a significant number of neutrinos. Neutrino detectors are often built underground to isolate the detector from [[w:cosmic ray|cosmic ray]]s and other background radiation.<ref name="twsP14">{{cite book
 |author= Ian Sample
 |title= The hunt for neutrinos in the Antarctic, In: ''The Guardian''
 |date= 23 January 2011
 |url= http://www.guardian.co.uk/science/2011/jan/23/neutrino-cosmic-rays-south-pole
 |accessdate= 2011-06-16 }}</ref> The field of [[neutrino astronomy]] is still very much in its infancy &ndash; the only confirmed extraterrestrial sources so far are the [[Sun (star)tars/Sun|Sun]] and [[w:SN1987A|supernova SN1987A]]. Various detection methods have been used. [[w:Super Kamiokande|Super Kamiokande]] is a large volume of water surrounded by [[w:phototube|phototube]]s that watch for the [[w:Cherenkov radiation|Cherenkov radiation]] emitted when an incoming neutrino creates an [[electron]] or [[w:muon|muon]] in the water. The [[w:Sudbury Neutrino Observatory|Sudbury Neutrino Observatory]] is similar, but uses [[w:heavy water|heavy water]] as the detecting medium. Other detectors have consisted of large volumes of [[w:chlorine|chlorine]] or [[w:gallium|gallium]] which are periodically checked for excesses of [[w:argon|argon]] or [[w:germanium|germanium]], respectively, which are created by neutrinos interacting with the original substance. [[w:MINOS|MINOS]] uses a solid plastic [[w:scintillator|scintillator]] watched by phototubes, [[w:Borexino|Borexino]] uses a liquid [[w:pseudocumene|pseudocumene]] scintillator also watched by phototubes while the proposed [[w:NOνA|NOνA]] detector will use liquid scintillator watched by [[w:avalanche photodiode|avalanche photodiode]]s.
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==Gamma rays==
{{main|Radiation astronomy/Gamma rays|Gamma rays}}
[[Image:HPGe detector90.jpg|thumb|center|250px|High-purity germanium detector (disconnected from liquid nitrogen dewar) is imaged. Credit: [[w:User:Sergio.ballestrero|Sergio.ballestrero]].]]
[[Image:Annihilation Radiation.JPG|thumb|right|2050px|A Germanium detector spectrum shows the electron-positron annihilation radiation peak (under the arrow). Note the width of the peak compared to the other gamma rays visible in the spectrum. Credit: Hidesert.]]
Germanium detectors are mostly used for spectroscopy in nuclear physics. Germanium can have a depleted, sensitive thickness of centimeters, and therefore can be used as a total absorption detector for gamma rays up to few MeV. These detectors are also called '''high-purity germanium''' detectors (HPGe) or hyperpure germanium detectors. Germanium crystals were doped with lithium ions (Ge(Li)), in order to produce an intrinsic region in which the electrons and holes would be able to reach the contacts and produce a signal. HPGe detectors commonly use lithium diffusion to make an n<sup>+</sup> ohmic contact, and boron implantation to make a p<sup>+</sup> contact. Coaxial detectors with a central n<sup>+</sup> contact are referred to as n-type detectors, while p-type detectors have a p<sup>+</sup> central contact. The thickness of these contacts represents a dead layer around the surface of the crystal within which energy depositions do not result in detector signals.
{{clear}}

==X-rays==
{{main|Radiation astronomy/X-rays|X-rays}}
[[Image:Proportional Counter Array RXTE.jpg|thumb|right|2050px|This is an image of a real X-ray detector. The instrument is called the Proportional Counter Array and it is on the [[w:Rossi X-ray Timing Explorer|Rossi X-ray Timing Explorer]] (RXTE) satellite. Credit: NASA.]]
[[Image:Suzaku HXD.jpg|thumb|left|2050px|The Suzaku Hard X-ray Detector is imaged before installation to the satellite. Credit: NASA.]]
Detectors such as the X-ray detector at right collect individual X-rays (photons of X-ray light), count them, discern the energy or wavelength, or how fast they are detected.

(contracted; show full)
{{main|Radiation astronomy/Ultraviolets|Ultraviolets}}
The dispersed ultraviolet light [from the [[w:Far Ultraviolet Spectroscopic Explorer|FUSE]] telescope] is detected by two [[w:microchannel plate detector|microchannel plate]] intensified double delay-line detectors, whose surfaces are curved to match the curvature of the focal plane.<ref name="Sahnow">{{cite book
|url=http://fuse.pha.jhu.edu/papers/technical/aas95/aas95.html
|title=The Far Ultraviolet Spectroscopic Explorer Mission

|work=JHU.edu⏎
|author=D.J. Sahnow, et al.
|date=1995-07-03
|accessdate=2007-09-07 }}</ref>

Two mirror segments are coated with silicon carbide for reflectivity at the shortest ultraviolet wavelengths, and two mirror segments are coated with lithium fluoride over aluminum that reflects better at longer wavelengths." Each segment such as with silicon carbide has a dedicated microchannel plate. The other microchannel plates are for the lithium fluoride mirror system.

(contracted; show full)|bibcode=
|doi=10.1103/PhysRevB.84.125203
|pmid=
|accessdate=2013-05-24 }}</ref>

==Violets==
{{main|Radiation astronomy/Violets|Violets}}
[[Image:Voyager - Filters - Violet.png|thumb|right|2
050px|The image shows the spectral range for the violet filter of Voyager 1 and Voyager 2. Credit: [[commons:User:Xession|Xession]].]]
Most spacecraft designed for [[optical astronomy]] or [[visual astronomy]] carry aboard a violet or blue filter covering the wavelength range from 350-430 nm. The Solid State Imaging camera of the Galileo spacecraft uses a broad-band filter centered at 404 nm for [[violet astronomy]].

The Hubble Space Telescope has throughout its long life used a variety of violet broad and narrow band filters for violet astronomy. The Wide Field Planetary Camera (PC-1) in use from about 1990 through 1993 carried the violet band filters: F330W, F336W, F344N, F368M, F375N, F413M, F435W, F437N, F439W, and F469N. The Wide Field Planetary Camera (PC-2) replaced PC-1 and carried the following violet filters on the same filter wheels: F300W, F336W, F343N, F375N, F380W, F390N, F410M, F437N, F439W, F450W, F467M and F469N.

The violet filter on each of the Viking Orbiters is centered at 440 nm with a range of 350-470 nm.

At right is an image of the spectral range of the Violet filter (50 to 400 nm)<ref name="Benesh">{{cite book
|author=M. Benesh and F. Jepsen
|title=SP-474 Voyager 1 and 2 Atlas of Six Saturnian Satellites Appendix A The Voyager Mission
|publisher=NASA
|location=Washington, DC USA
|monthdate=August 6,⏎
|year=  1984
|url=http://history.nasa.gov/SP-474/appa.htm
|accessdate=2013-04-01 }}</ref> on the Imaging Science System aboard the Voyager 1 and Voyager 2 Spacecraft, as defined by the instrument descriptions of the Narrow Angle Camera and Wide Angle Camera.
{{clear}}

==Blues==
{{main|Radiation astronomy/Blues|Blues}}
In about 1981 "an efficient blue- and violet-sensitive RCA CCD did appear on the market."<ref name="Oke">{{cite journal
(contracted; show full)

The blue- and violet-sensitive CCD successfully detected the helium lines from 501.5 to 318.8 nm.<ref name="Oke"/>

"The MIC (Microchannel plate Intensified CCD (Charge Coupled Device)) detector ... [has a] measured resolution of the detector system [of] 18 micrometers FWHM at 490 nm. [It is] for the ESA X-Ray Multi Mirror Mission (XMM), where the MIC has been accepted as the blue detector for the incorporated Optical Monitor (OM)."<ref name=
"Thomsen"Fordham>{{cite book
|author=J. L. A. Fordham, D. A. Bone, M. K. Oldfield, J. G. Bellis, and T. J. Norton
|title=The MIC photon counting detector, In: ''Proceedings of an ESA Symposium on Photon Detectors for Space Instrumentation''
|publisher=European Space Agency
|location=
|monthdate=December⏎
|year=  1992
|editor=
|pages=103-6
|url=
|arxiv=
|bibcode=1992ESASP.356..103F
|doi=
|pmid=
|isbn=
|accessdate=2013-05-24 }}</ref>

"A0620-00 [is observed] with the [Faint Object Spectrograph] FOS blue detector" while aboard the Hubble Space Telescope.<ref name="McClintock">{{cite book
|author=Jeffrey McClintock
|title=Black Hole A0620-00 and Advection-Dominated Accretion, In: ''HST Proposal ID #7393''
|publisher=STSci
|location=Baltimore, Maryland USA
|monthdate=December⏎
|year=  1997
|editor=
|pages=
|url=
|arxiv=
|bibcode=1997hst..prop.7393M
|doi=
|pmid=
|isbn=
|accessdate=2013-05-24 }}</ref>

==Cyans==
{{main|Radiation astronomy/Cyans|Cyans}}
The Wide Field/Planetary Camera (PC-1) had an F469N, F487N, and F492M cyan filters in the filter wheel.<ref name="Krist"/>

The Wide Field Planetary Camera (PC-2) replaced PC-1 on the Hubble Space Telescope and carried the following cyan filters on the same filter wheels: F467M, F469N, F487N.<ref name="Krist">{{cite book
|author=John Krist and Richard Hook
|title=The Tiny Tim User’s Guide, Version 6.3
|publisher=Space Telescope Science Institute
|location=
|month=June
|year=date=June 2004
|url=http://tinytim.stsci.edu/static/tinytim.pdf
|accessdate=2013-01-22 }}</ref>

The Advanced Camera for Surveys carried an F475W broadband cyan filter.<ref name="Krist"/>

The Faint Object Camera (FOC) carries F470M, F480LP, and F486N cyan filters.<ref name="Krist"/>

(contracted; show full)|pages = 6251–6256
|url = http://www.opticsinfobase.org/ao/abstract.cfm?uri=ao-47-33-6251
|pmid = 19023391
|bibcode = 2008ApOpt..47.6251P }}</ref>

==Radios==
{{main|Radiation astronomy/Radios|Radio astronomy|Radios}}
[[Image:Coherer.jpg|right|thumb|
250px|A metal filings coherer is imaged. Credit: [[w:User:JA.Davidson|JA.Davidson]].]]
The '''coherer''' consists of a tube or capsule containing two [[w:electrode|electrode]]s spaced a small distance apart, with metal filings in the space between them. When a [[w:radio frequency|radio frequency]] signal is applied to the device, the initial high [[w:resistance (electricity)|resistance]] of the filings reduces, allowing an electric current to flow through it.
{{clear}}

==Superluminals==
{{main|Radiation astronomy/Superluminals|Superluminals}}
[[Image:Lhcbview.jpg|thumb|left|2050px|LHCb detector is diagrammed. Credit: [[w:User:Oswald_le_fort|Oswald_le_fort]].]]
[[Image:Alpha Magnetic Spectrometer - 02.jpg|thumb|right|2050px|AMS-02 is a RICH detector for analyzing cosmic rays. Credit: NASA.]]
Most Cherenkov detectors aim at recording the Cherenkov light produced by a primary charged particle. Some sensor technologies explicitly aim at Cherenkov light produced (also) by secondary particles, be it incoherent emission as occurring in an electromagnetic particle shower or by coherent emission, example Askaryan effect.

(contracted; show full)|year=2012 }}</ref>

The [[w:Alpha Magnetic Spectrometer|Alpha Magnetic Spectrometer]] device AMS-02, recently mounted on the [[w:International Space Station|International Space Station]] uses a RICH detector in combination with other devices to analyze cosmic rays.
{{clear}}

==Plasma objects==
{{main|Plasmas/Plasma objects|Plasma objects}}
[[Image:faraday cup.jpg|thumb|right|2
050px|This is a Faraday cup with an electron-suppressor plate in front. Credit: [[commons:User:Angelpeream|Angelpeream]].]]
A '''Faraday cup''' is a metal (conductive) cup designed to catch [[w:charged particle|charged particle]]s in vacuum. The resulting current can be measured and used to determine the number of ions or electrons hitting the cup.<ref name="Brown">{{cite journal
|title=Faraday-Cup Monitors for High-Energy Electron Beams
(contracted; show full)
|title=Ultra-low power hydrogen sensing based on a palladium-coated nanomechanical beam resonator
|author=Jonas Henriksson
|journal=Nanoscale Journal
|accessdate=2013-02-26 }}</ref>

==Liquid objects==
{{main|Liquids/Liquid objects|Liquid objects}}
[[Image:Hot and cold water immiscibility thermal image.jpg|thumb|right|2
050px|Thermal image of a sink full of hot water with cold water being added shows the hot and the cold water flowing into each other. Credit: [[commons:User:Zaereth|Zaereth]].]]
[[Image:Water drop 001.jpg|thumb|2050px|left|The formation of a spherical [[w:Drop (liquid)|droplet]] of liquid water minimizes the [[w:surface area|surface area]], which is the natural result of [[w:surface tension|surface tension]] in liquids. Credit: [http://www.flickr.com/photos/josjos/2631718740/ José Manuel Suárez].]]
A liquid is made up of tiny vibrating particles of matter, such as atoms and molecules, held together by intramolecular bonds. ... Although liquid water is abundant on Earth, this state of matter is actually the least common in the known universe, because liquids require a relatively narrow temperature/pressure range to exist.

The first image at right shows liquid water using an infrared detector, but information confirming the presence of liquid water solely from the infrared image is inferred.

The image at left uses a visual radiation detector to record a meteor collision with liquid water.

Reconstructions of seismic waves in the deep interior of the Earth show that there are no [[w:S-waves|S-waves]] in the [[w:outer core|outer core]]. This indicates that the outer core is liquid, because liquids cannot support shear. The outer core is liquid, and the motion of this highly conductive fluid generates the Earth's field (see [[w:geodynamo|geodynamo]]).
{{clear}}

==Rocky objects==
{{main|Rocks/Rocky objects|Rocky objects}}
[[Image:Venus globe.jpg|thumb|left|2050px|This is a false color image of Venus produced from a global [[w:Radar|radar]] view of the surface by the [[w:Magellan probe|Magellan probe]] while radar imaging between 1990-1994. Credit: NASA.]]
Often a rocky object is detected by the observation of impact craters usually using [[visual astronomy]] as part of [[crater astronomy]].

"A number of bright spots with a bluish tinge are visible ... These are relatively recent impact craters. Some of the bright craters have bright streaks ... emanating from them. Bright features such as these are caused by the presence of freshly crushed rock material that was excavated and deposited during the highly energetic collision of a meteoroid with Mercury to form an impact crater."<ref name="JHUAPL">{{cite book
|author=JHU/APL
|title=Mercury Shows Its True Colors
|publisher=JHU/APL
|location=Baltimore, Maryland USA
|monthdate=January 30,⏎
|year=  2008
|url=http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?page=1&gallery_id=2&image_id=143
|accessdate=2013-04-01 }}</ref>

The object at left is detected to be a rocky object using [[radar astronomy]].

"The advantages of radar in planetary astronomy result from (1) the observer's control of all the attributes of the coherent signal used to illuminate the target, especially the wave form's time/frequency modulation and polarization; (2) the ability of radar to resolve objects spatially via measurements of the distribution of echo power in time delay and Doppler frequency; (3) the pronounced degree to which delay-Doppler measurements constrain orbits and spin vectors; and (4) centimeter-to-meter wavelengths, which easily penetrate optically opaque planetary clouds and cometary comae, permit investigation of near-surface macrostructure and bulk density, and are sensitive to high concentrations of metal or, in certain situations, ice."<ref name="Ostro">{{cite journal
|author=Steven J. Ostro
|title=Planetary radar astronomy
|journal=Reviews of Modern Physics
|month=October-December
|year=1993
|volume=65
|issue=4
|pages=1235-79
|url=http://rmp.aps.org/abstract/RMP/v65/i4/p1235_1
|arxiv=
|bibcode=
|doi=10.1103/RevModPhys.65.1235
|pmid=
|accessdate=2012-02-09 }}</ref>
{{clear}}

==Astrochemistry==
{{main|Astrochemistry}}
[[Image:XRFScan.jpg|thumb|right|2050px|Typical energy dispersive XRF spectrum for a number of elements is shown. Credit: [[w:User:LinguisticDemographer|LinguisticDemographer]].]]
Each element has electronic orbitals of characteristic energy. Following removal of an inner electron by an energetic photon provided by a primary radiation source, an electron from an outer shell drops into its place. There are a limited number of ways in which this can happen ... The main transitions are given names: an L→K transition is traditionally called Kα, an M→K transition is called Kβ, an M→L transition is called Lα, and so on. Each of these transitions yields a fluorescent photon with a characteristic energy equal to the difference in energy of the initial and final orbital.
{{clear}}

==Compounds==
{{main|Chemicals/Compounds|Compounds}}
(contracted; show full)ncreased. These time differences were minute, but the improvement in electronics made it possible to measure them accurately and identify the presence of metal at a reasonable distance. These new machines had one major advantage: they were completely impervious to the effects of mineralization, and rings and other jewelry could now be located even under highly-mineralized black sand.

==Sun==
{{main|Stars/Sun|Sun (star)}}
A ''sun sensor'' is a device that senses the direction to the [[S
un (star)tars/Sun|Sun]]. This can be as simple as some [[w:solar cell|solar cell]]s and shades, or as complex as a steerable [[w:telescope|telescope]], depending on mission requirements.

==Earth==
{{main|Earth}}
An ''earth sensor'' is a device that senses the direction to the [[Earth]]. It is usually an infrared camera; now the main method to detect attitude is the star tracker, but earth sensors are still integrated in satellites for their low cost and reliability.

==Stars==
{{main|Stars}}
A ''star tracker'' is an optical device that measures the position(s) of [[w:star|star]](s) using [[w:photocell|photocell]](s) or a camera.<ref>{{cite book|title=Star Camera|url=http://web.archive.org/web/20110721054014/http://nmp.nasa.gov/st6/TECHNOLOGY/star_camera.html|publisher=NASA|accessdate=25 May 2012|date=05/May 2004}}</ref>

Star trackers, which require high sensitivity, may become confused by sunlight reflected from the spacecraft, or by exhaust gas plumes from the spacecraft thrusters (either sunlight reflection or contamination of the star tracker window). Star trackers are also susceptible to a variety of errors (low spatial frequency, high spatial frequency, temporal, ...) in addition to a variety of optical sources of error ([[w:spherical aberration|spherical aberration]], [[w:chromatic aberration|chroma(contracted; show full)

==Geography==
{{main|Geography}}
Occasionally, a detector needs a specific geographic property for optimal function.

===Large surface area===
[[Image:PierreAugerObservatory DetectorComponents.jpg|thumb|2
050px|right|Surface detector station and AERA radio antenna is in the foreground, one of the four fluorescence detector buildings and the three HEAT telescopes is in the background. Credit: [[commons:User:Tobias Winchen|Tobias Winchen]].]]
The '''Pierre Auger Observatory''' is an international cosmic ray observatory designed to detect [[w:ultra-high-energy cosmic ray|ultra-high-energy cosmic ray]]s: single [[w:sub-atomic particle|sub-atomic particle]]s ([[w:proton|proton]]s or [[w:Atomic nucleus|atomic nuclei]]) with energies beyond 10<sup>20</sup>&nbsp;[[w:electronvolt|eV]] (about the energy of a [[w:tennis ball|tennis ball]] traveling at 80&nbsp;km/h). These high energy particles have an estimated arrival rate of just 1 per km<sup>2</sup> per century, therefore the Auger Observatory has created a detection area the size of [[w:Rhode Island|Rhode Island]] — over 3,000 km<sup>2</sup> (1,200 sq mi) — in order to record a large number of these events. It is located in western [[w:Argentina|Argentina]]'s [[w:Mendoza Province|Mendoza Province]], in one of the South American [[w:Pampas|Pampas]].
{{clear}}

===Next to water===
[[Image:Old dome of the Big Bear Solar Observatory (Big Bear Lake, California).jpg|thumb|right|2050px|The old dome on the main BBSO building is viewed from Big Bear Lake. Credit: [[w:User:Magi Media|Magi Media]].]]
The '''Big Bear Solar Observatory''' (BBSO) is a [[w:solar observatory|solar observatory]] located on the north side of [[w:Big Bear Lake|Big Bear Lake]] in the [[w:San Bernardino Mountains|San Bernardino Mountains]] of southwestern [[w:San Bernardino County|San Bernardino County]], [[w:California|California]] (USA), approximately 120 kilometers (75 mi) east of d(contracted; show full)amp;nbsp;km under the [[w:Mediterranean Sea|Mediterranean Sea]] off the coast of Toulon, France. It is designed to be used as a directional ''Neutrino Telescope'' to locate and observe neutrino flux from cosmic origins in the direction of the [[w:Southern Hemisphere|Southern Hemisphere]] of the [[Earth]], a complement to the southern hemisphere neutrino detector [[w:IceCube|IceCube]] that detects neutrinos from the North.

==History==
{{main|History}}
[[Image:Oso5 wheel.gif|thumb|left|2
050px|The figure of the OSO 5 wheel contains detectors for gamma-rays, X-rays, ultraviolet, and visible (Zodiacal light). Credit: HEASARC, NASA.]]
[[Image:Oso5 NRLxrd.gif|thumb|right|250px|The diagram of the Naval Research Laboratory Solar X-ray Radiation Ion Chamber Photometer shows the location of the center crystal. Credit: NASA.]]
[[Image:Skylark X-ray detector, World Museum Liverpool.jpg|thumb|right|2050px|This is an image of the X-ray detector dedicated to use aboard Skylark sounding rockets. Credit: Reptonix.]]
"The wheel of the [OSO 5] satellite carried, amongst other experiments, a CsI crystal scintillator. The central crystal was 0.635 cm thick, had a sensitive area of 70 sq-cm, and was viewed from behind by a pair of photomultiplier tubes. The shield crystal had a wall thickness of 4.4 cm and was viewed by 4 photomultipliers. The field of view was ~ 40 degrees. The energy range covered was 14-254 keV. There were 9 energy channels: the first covering 14-28 keV and the others equally spaced from 28-254 keV. In-flight calibration was done with an 241 Am source. The instrument was designed primarily for observation of solar X-ray bursts. A secondary interest was the measurement of the intensity, spectrum, and spatial distribution of the diffuse cosmic background. The data produced a spectrum of the diffuse background over the energy range 14-200 keV."<ref name="Heasarc">{{cite book
|author=Heasarc
|title=OSO-5
|publisher=NASA GSFC
|location=Greenbelt, Maryland USA
|monthdate=June 26,⏎
|year=  2003
|url=http://heasarc.gsfc.nasa.gov/docs/heasarc/missions/oso5.html
|accessdate=2013-05-18 }}</ref>
{{clear}}

==Mathematics==
{{main|Mathematics}}
The energy differences between levels in the Bohr model, and hence the wavelengths of emitted/absorbed photons, is given by the Rydberg formula<ref name="Bohr">{{citatione book
|author=Niels Bohr
|chaptertitle=Rydberg's discovery of the spectral laws⏎
|editor=J. Kalckar
|title=, In: ''N. Bohr: Collected Works''
|editor=J. Kalckar
|publisher=North-Holland Publ.
|location=Amsterdam
|yeardate=1985
|volume=10
|pages=373–9 }}</ref>:

:<math> {1 \over \lambda} = R \left( {1 \over (n^\prime)^2} - {1 \over n^2} \right) \qquad \left( R = 1.097373 \times 10^7 \ \mathrm{m}^{-1} \right)</math>
(contracted; show full)velocity of light) then <math>\beta_T^{max} > 1</math> despite the fact that <math>\beta < 1</math>. And of course <math>\beta_T > 1</math> means apparent transverse velocity along CB, the only velocity on sky that we can measure, is larger than the velocity of light in vacuum, i.e. the motion is apparently superluminal.

==Gas-chamber detectors==
{{main|Radiation astronomy/Detectors/Gas chambers|Gas-chamber detectors}}
[[Image:Detector regions.gif|thumb|right|2
050px|This is a plot of ion current as function of applied voltage for a wire cylinder gaseous radiation detector. Credit: [[commons:User:Dougsim|Doug Sim]].]]
(contracted; show full)

==Scintillation detectors==
{{main|Radiation astronomy/Detectors/Scintillations|Scintillation detectors}}
[[Image:Scintillation Counter Schematic.jpg|right|2
050px|thumb|Schematic showing incident particles hitting a scintillating crystal, triggering the release of photons which are then converted into [[w:photoelectrons|photoelectrons]] and multiplied in the [[w:photomultiplier|photomultiplier]]. Credit: [[commons:User:Manticorp|Manticorp]].]]
[[Image:Scintillation Detector.gif|thumb|right|2050px|This is an animation of a radiation scintillation counter. Credit: [[b:User:KieranMaher|KieranMaher]].]]
Some materials such as sodium iodide (NaI) can "convert" an X-ray photon to a visible photon; an electronic detector can be built by adding a photomultiplier. These detectors are called "scintillators", filmscreens or "scintillation counters".

(contracted; show full)#x27;' When their sensitive structures are based on a single [[w:diode|diode]], they are called '''semiconductor diode detectors'''. When they contain many diodes with different functions, the more general term semiconductor detector is used. Semiconductor detectors have found broad application during recent decades, in particular for [[w:gamma ray|gamma]] and [[w:X-ray|X-ray]] [[w:spectrometry|spectrometry]] and as [[w:particle detector|particle detector]]s.

[[Radiation
/Keynote lecture|[R]adiation]] is measured by means of the number of [[w:charge carrier|charge carrier]]s set free in the detector, which is arranged between two [[w:electrode|electrode]]s. Ionizing radiation produces free [[electron]]s and [[w:Electron hole|holes]]. The number of electron-hole pairs is proportional to the [[w:energy|energy]] transmitted by the radiation to the semiconductor. As a result, a number of electrons are transferred from the [[w:valence band|valence band]] to the [[w:conduction band|conduction band]], and an equal number of holes are created in the valence band. Under the influence of an [[w:electric field|electric field]], electrons and holes travel to the electrodes, where they result in a pulse that can be measured in an outer [[w:electrical network|circuit]], as described by the [[w:Shockley-Ramo Theorem|Shockley-Ramo Theorem]]. The holes travel in the opposite direction and can also be measured. As the amount of energy required to create an electron-hole pair is known, and is independent of the energy of the incident radiation, measuring the number of electron-hole pairs allows the energy of the incident radiation to be found.<ref name="Knoll">{{cite book
|author=G. F. Knoll
|title=Radiation Detection and Measurement, 3rd edition
|publisher=Wiley
|yeardate=1999
|isbn=978-0471073383 }}</ref>

Semiconductors have been used for neutron detection.<ref name="Miroshghi">{{cite journal
 | author = Mireshghi A., Cho, G.; Drewery, J.S.; Hong, W.S.; Jing, T.; Lee, H.; Kaplan, S.N.; Perez-Mendez, V.
 | title = High efficiency neutron sensitive amorphous silicon pixel detectors
 | journal = Nuclear Science
 | volume = 41
(contracted; show full)ge. Although silicon has outstanding electronic properties, it is not a particularly good absorber of X-ray photons. For this reason, X-rays first impinge upon scintillators made from such materials as gadolinium oxysulfide or caesium iodide. The scintillator absorbs the X-rays and converts them into visible light photons that then pass onto the photodiode array.

==Hypotheses==
{{main|Hypotheses}}
# Radiation detectors can be built to differentiate between superluminal, luminal, and subluminal radiations.
⏎
{{seealso|Control groups|Proof of concept|Proof of technology}}

==See also==
{{div col|colwidth=12em}}
* [[Principles of Radiation Astronomy]]
* [[Radiation]]
* [[Radiation astronomy astronomy/Keynote lecture]]
* [[Radiation/Keynote lecture]]
{{Div col end}}

==References==
{{reflist|2}}

==Further reading==
* {{cite book
 | author=C. Grupen
 | title=Physics of Particle Detection⏎
 | booktitle=, In: ''AIP Conference Proceedings, Instrumentation in Elementary Particle Physics, VIII''
 | pages=3&ndash;34 | volume=536
 | publisher=Dordrecht, D. Reidel Publishing Co.
 | date=June 28-July 10, 1999
 | location=Istanbul
 | doi=10.1063/1.1361756 }}
* "''Radiation detectors''". H. M. Stone Productions, Schloat. Tarrytown, N.Y., Prentice-Hall Media, 1972.

==External links==
* [http://www.bing.com/search?q=&go=&qs=n&sk=&sc=8-15&qb=1&FORM=AXRE Bing Advanced search]
* [http://books.google.com/ Google Books]
(contracted; show full)* [http://www.springerlink.com/ SpringerLink]
* [http://www.tandfonline.com/ Taylor & Francis Online]
* [http://www.wikidoc.org/index.php/Main_Page WikiDoc The Living Textbook of Medicine]
* [http://onlinelibrary.wiley.com/advanced/search Wiley Online Library Advanced Search]
* [http://search.yahoo.com/web/advanced Yahoo Advanced Web Search]

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