WordNet

name or recite the numbers in ascending order; "The toddler could count to 100"
the total number counted; "a blood count"
the act of counting; reciting numbers in ascending order; "the counting continued for several hours" (同)counting, numeration, enumeration, reckoning, tally
a nobleman (in various countries) having rank equal to a British earl
have faith or confidence in; "you can count on me to help you any time"; "Look to your friends for support"; "You can bet on that!"; "Depend on your family in times of crisis" (同)bet, depend, look, calculate, reckon
have weight; have import, carry weight; "It does not matter much" (同)matter, weigh
put into a group; "The academy counts several Nobel Prize winners among its members" (同)number
determine the number or amount of; "Can you count the books on your shelf?"; "Count your change" (同)number, enumerate, numerate
have a certain value or carry a certain weight; "each answer counts as three points"
include as if by counting; "I can count my colleagues in the opposition"
speak in response; "He countered with some very persuasive arguments"
a piece of leather forming the back of a shoe or boot; "a counter may be used to stiffen the material around the heel and to give support to the foot" (同)heel counter
a calculator that keeps a record of the number of times something happens (同)tabulator
(computer science) a register whose contents go through a regular series of states (usually states indicating consecutive integers)
game equipment (as a piece of wood, plastic, or ivory) used for keeping a count or reserving a space in various card or board games
table consisting of a horizontal surface over which business is transacted
a person who counts things
in the opposite direction; "run counter"
(physics) a flash of light that is produced in a phosphor when it absorbs a photon or ionizing particle
the twinkling of the stars caused when changes in the density of the earths atmosphere produce uneven refraction of starlight
a brilliant display of wit

PrepTutorEJDIC

(一つ一つ順に)〈数〉'を'『数える』,〈物〉'を'数え上げる《+『up』+『名,』+『名』+『up』》 / …'を'『勘定に入れる』,含める(include) / …'を'『思う』,みなす(consider) / 数を数える,計算する《+『up』》 / 数にはいる,数に含まれる / 価値がある,重大である / 〈C〉〈U〉『数えること』,『計算』 / 〈U〉総数,総計 / 〈U〉(起訴状の)訴因 / 《the~》(ボクシングで)カウント(選手がノックダウンされたときレフリーが1から10まで数えること) / 〈C〉(野救で打者の)ボールカウント / 〈U〉《話》考慮,注目(account)
(英国以外の)伯爵
(商店・銀行などの)『売り台』,勘定台,カウンター / (食堂などに)『カウンター』 / (おもちゃの)模造貨幣
計算する人 / (特に電動式の)計算器,計数器 / (ゲームの得点計算用)数取り,点棒
『反対の』,逆の(opposite) / (一対の)片方の,副の / (…と)反対に,逆に《+『to』+『名』》 / …‘に'『逆らう』,立ち向かう / …'を'無効にする / (ボクシングなどで)〈打撃〉'を'返す,‘に'反撃する / (ボクシングなどで)打ち返す / 『逆』,反対,対立物 / (フェンシングの)受け流し / (ボクシングなどで)打ち返し,カウンター / (靴の)かかとの皮
火花,きらめき / 才気のひらめき

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2012/09/20 00:23:10」(JST)

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Schematic showing incident particles hitting a scintillating crystal, triggering the release of photons which are then converted into photoelectrons and multiplied in the photomultiplier.

A scintillation counter measures ionizing radiation. The sensor, called a scintillator, consists of a transparent crystal, usually phosphor, plastic (usually containing anthracene) or organic liquid (see liquid scintillation counting) that fluoresces when struck by ionizing radiation.

A sensitive photomultiplier tube (PMT) measures the light from the crystal, and the output signal is fed to an electronic amplifier and other electronic equipment to count and possibly quantify the amplitude of the signals produced by the photomultiplier.

Scintillation counters are widely used because they can be made inexpensively yet with good quantum efficiency.

Scintillator/photomultipier combined operation

animation of radiation scintillation counter

When a charged particle strikes the scintillator, the phosphor's atoms are excited and emit photons, which are directed at the photomultiplier tube's photocathode which is connected to the negative of a high voltage source. Each incident photon releases an electron. A number of accelerating electrodes called dynodes are arranged in the tube at increasing positive potentials and the electron is accelerated by this electric field towards the first dynode. The incident electron causes multiple secondary electrons to be emitted, which accelerate towards and hit the second dynode. More electrons are emitted and the electron multiplication chain continues through the increasing potentials of the dynodes, with increasing numbers of electrons generated each time. By the time the electrons reach the anode, enough have been released to generate a measurable voltage pulse across external resistors. This voltage pulse is amplified and recorded by the processing electronics.

The scintillator must be in complete darkness so that visible light photons do not swamp the individual photon events caused by incident ionising radiation. A thin opaque foil, such as aluminised mylar, is used to achieve this, though it must have a low enough mass to prevent attenuation of the incident radiation that is being measured.

Detection materials

Cesium iodide (CsI) in crystalline form is used as the scintillator for the detection of protons and alpha particles. sodium iodide (NaI) containing a small amount of thallium is used as a scintillator for the detection of gamma waves and Zinc Sulphide is widely used as a detector of alpha particles.

Detector efficiencies

The quantum efficiency of a gamma-ray detector (per unit volume) depends upon the density of electrons in the detector, and certain scintillating materials, such as sodium iodide and bismuth germanate, achieve high electron densities as a result of the high atomic numbers of some of the elements of which they are composed. However, detectors based on semiconductors, notably hyperpure germanium, have better intrinsic energy resolution than scintillators, and are preferred where feasible for gamma-ray spectrometry. In the case of neutron detectors, high efficiency is gained through the use of scintillating materials rich in hydrogen that scatter neutrons efficiently. Liquid scintillation counters are an efficient and practical means of quantifying beta radiation.

Applications

Alpha scintillation probe under calibration

Scintillation counters are used to measure radiation in a variety of applications.

Hand held radiation survey meters
Personnel and environmental monitoring for Radioactive contamination
Medical imaging
National and homeland security
Border security
Nuclear plant safety
Radon levels in water

Several products have been introduced in the market utilising scintillation counters for detection of potentially dangerous gamma-emitting materials during transport. These include scintillation counters designed for freight terminals, border security, ports, weigh bridge applications, scrap metal yards and contamination monitoring of nuclear waste. There are variants of scintillation counters mounted on pick-up trucks and helicopters for rapid response in case of a security situation due to dirty bombs or radioactive waste.^[1]^[2] Hand-held units are also commonly used.^[3]

Alpha and Beta contamination detection

The industrial contamination monitoring detector, consisting of a scintillator and photomultiplier tube, finds wide application in the field of radioactive contamination monitoring of personnel and the environment. Detectors are designed to have one or two scintillation materials, depending on the application. Such as zinc sulphide is used for alpha particle detection, whilst plastic scintillators are used for beta detection. The resultant scintillation energies can be discriminated so that alpha and beta counts can be measured separately with the same detector. "Single phosphor" detectors are used for either alpha or beta, and "Dual phosphor" detectors are used to detect both. These detectors are used in both hand-held and fixed monitoring equipment. Such instruments are relatively inexpensive compared with the gas proportional detector. They are also able to discriminate between alpha and beta, which the Geiger tube cannot.

Scintillation counter as a spectrometer

The experimental setup for determination of γ-radiation spectrum with a scintillation counter. A high voltage power supply is connected to the scintillation counter. The scintillation counter is connected to the Multichannel Analyser which sends information to the computer.

Scintillators often convert a single photon of high energy radiation into high number of lower-energy photons, where the number of photons per megaelectronvolt of input energy is fairly constant. By measuring the intensity of the flash (the number of the photons produced by the x-ray or gamma photon) it is therefore possible to discern the original photon's energy.

The spectrometer consists of a suitable scintillator crystal, a photomultiplier tube, and a circuit for measuring the height of the pulses produced by the photomultiplier. The pulses are counted and sorted by their height, producing a x-y plot of scintillator flash brightness vs number of the flashes, which approximates the energy spectrum of the incident radiation, with some additional artifacts. A monochromatic gamma radiation produces a photopeak at its energy. The detector also shows response at the lower energies, caused by Compton scattering, two smaller escape peaks at energies 0.511 and 1.022 MeV below the photopeak for the creation of electron-positron pairs when one or both annihilation photons escape, and a backscatter peak. Higher energies can be measured when two or more photons strike the detector almost simultaneously (pile-up, within the time resolution of the data acquisition chain), appearing as sum peaks with energies up to the value of two or more photopeaks added.^[4]

History

The modern electronic scintillation counter was invented in 1944 by Sir Samuel Curran^[5]^[6] whilst he was working on the Manhattan Project at the University of California at Berkeley, and it is based on the work of earlier researchers reaching back to Antoine Henri Becquerel, who is generally credited with discovering radioactivity, whilst working on the phosphorescence of certain uranium salts (in 1896). The Spinthariscope was a early method of detecting the scintillation events by eye.

References

^ Automatic Radiation Detection and Monitoring System
^ Automatic Radiation Detection Vehicles
^ Portable MicroR Survey Meters
^ Knoll, Glenn (1999). Radiation Detection and Measurement. John Wiley and Sons. ISBN 0-471-07338-5
^ "Counting tubes, theory and applications", Curran, Samuel C., Academic Press (New York), 1949
^ Oxford Dictionary of National Biography

UpToDate Contents

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English Journal

Sample volume optimization for radon-in-water detection by liquid scintillation counting.

Schubert M1, Kopitz J2, Chałupnik S3.
Journal of environmental radioactivity.J Environ Radioact.2014 Aug;134:109-13. doi: 10.1016/j.jenvrad.2014.03.005. Epub 2014 Apr 3.
Radon is used as environmental tracer in a wide range of applications particularly in aquatic environments. If liquid scintillation counting (LSC) is used as detection method the radon has to be transferred from the water sample into a scintillation cocktail. Whereas the volume of the cocktail is ge
PMID 24704764

A simple-rapid method to separate uranium, thorium, and protactinium for U-series age-dating of materials.

Knight AW1, Eitrheim ES2, Nelson AW3, Nelson S4, Schultz MK5.
Journal of environmental radioactivity.J Environ Radioact.2014 Aug;134:66-74. doi: 10.1016/j.jenvrad.2014.02.010. Epub 2014 Mar 28.
Uranium-series dating techniques require the isolation of radionuclides in high yields and in fractions free of impurities. Within this context, we describe a novel-rapid method for the separation and purification of U, Th, and Pa. The method takes advantage of differences in the chemistry of U, Th,
PMID 24681438

First performance tests of a digital photon counter (DPC) array coupled to a CsI(Tl) crystal matrix for potential use in SPECT.

Georgiou M1, Borghi G, Spirou SV, Loudos G, Schaart DR.
Physics in medicine and biology.Phys Med Biol.2014 May 21;59(10):2415-30. doi: 10.1088/0031-9155/59/10/2415. Epub 2014 Apr 17.
The digital photon counter (DPC) is a recently developed type of digital silicon photomultiplier that combines low dark count rates, low readout noise, and fully digital, integrated readout circuitry with neighbor logic capability, system scalability, and MR compatibility. These are desirable proper
PMID 24743522