比例計数管

WordNet

counter tube whose output pulse is proportional to number of ions produced (同)proportional_counter
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"
give pleasant proportions to; "harmonize a building with those surrounding it"
the relation between things (or parts of things) with respect to their comparative quantity, magnitude, or degree; "an inordinate proportion of the book is given over to quotations"; "a dry martini has a large proportion of gin" (同)ratio
adjust in size relative to other things
the quotient obtained when the magnitude of a part is divided by the magnitude of the whole
magnitude or extent; "a building of vast proportions" (同)dimension
harmonious arrangement or relation of parts or elements within a whole (as in a design); "in all perfectly beautiful objects there is found the opposition of one part to another and a reciprocal balance"- John Ruskin (同)proportionality, balance
having a constant ratio
one of the quantities in a mathematical proportion
properly related in size or degree or other measurable characteristics; usually followed by `to; "the punishment ought to be proportional to the crime"; "earnings relative to production" (同)relative

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
《the~》(…に対する…の)『割合』,比率《+『of』+『名』+『to』+『名』》 / 〈U〉(…との)『調和』,均衡《+『to』+『名』》 / 〈C〉部分;割り前,分け前 / 《複数形で》大きさ / 〈U〉比例 / …‘の'調和をとる;(…に)…‘を'釣り合わせる《+『名』+『to』+『名』》
比例の,比例による;(…と)比例として《+『to』+『名』》 / 釣り合った,調和した;(…に)釣り合った《+『to』+『名』》

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/02/02 16:15:01」(JST)

wiki en

The proportional counter is a type of gaseous ionization detector device used to count particles of ionizing radiation. A key feature is its ability to measure the energy of incident radiation, and it is widely used where discrimination between radiation types is required, such as between alpha and beta particles.

Plot of variation of ion pair current against applied voltage for a wire cylinder gaseous radiation detector.

A proportional counter uses a combination of the mechanisms of a Geiger-Muller tube and an ionisation chamber, and operates in an intermediate voltage region between these. Considering a gas-filled chamber with a wire anode, if the field strength everywhere in the volume is below a critical value, Townsend avalanches do not occur at all, and the detector operates as an ionization chamber. If the applied voltage is too high, complete ionisation of the fill gas occurs with almost each ion pair and the detector operates as a Geiger-Müller counter, with the consequent loss of incident particle energy information. The accompanying plot shows the proportional operating region for a co-axial cylinder arrangement.

Operation

The generation of discrete Townsend avalanches in a proportional counter.

Plot of electric field strength at the anode, showing boundary of avalanche region.

In a proportional counter the fill gas of the chamber is an inert gas which is ionised by incident radiation, and a quench gas to ensure each pulse discharge terminates; a common mixture is 90% argon, 10% methane, known as P-10. An ionizing particle entering the gas collides with a molecule of the inert gas and ionises it to produce an electron and a positively charged atom, commonly known as an "ion pair". As the charged particle travels through the chamber it leaves a trail of ion pairs along its trajectory, the number of which is proportional to the energy of the particle if it is fully stopped within the gas. Typically a 1 MeV stopped particle will create about 30,000 ion pairs.^[1]

The chamber geometry and the applied voltage is such that in most of the chamber the electric field strength is low and the chamber acts as an ion chamber. However, the field is strong enough to prevent re-combination of the ion pairs and causes positive ions to drift towards the cathode and electrons towards the anode. This is the "ion drift" region. In the immediate vicinity of the anode wire, the field strength becomes large enough to produce Townsend avalanches. This avalanche region occurs only fractions of a millimeter from the anode wire, which itself is of a very small diameter. The purpose of this is to use the multiplication effect of the avalanche produced by each ion pair. This is the "avalanche" region.

A key design goal is that each original ionising event due to incident radiation produces only one avalanche. This is to ensure proportionality between the number of original events and the total ion current. For this reason the applied voltage, the geometry of the chamber and the diameter of the anode wire are critical to ensure proportional operation. If avalanches start to self-multiply due to UV photons as they do in a Geiger-Muller tube, then the counter enters a region of "limited proportionality" until at a higher applied voltage the Geiger discharge mechanism occurs with complete ionisation of the gas enveloping the anode wire and consequent loss of particle energy information.

Therefore it can be said that the proportional counter has the key design feature of two distinct ionisation regions:

Ion drift region: in the outer volume of the chamber - creation of number ion pairs proportional to incident radiation energy.
Avalanche region: in the immediate vicinity of the anode - Charge amplification of ion pair currents, while maintaining localised avalanches.

The process of charge amplification greatly improves the signal-to-noise ratio of the detector and reduces the subsequent electronic amplification required.

In summary, the proportional counter is an ingenious combination of two ionisation mechanisms in the one chamber which finds wide practical use.

Applications

Spectroscopy

The proportionality between the energy of the charged particle travelling through the chamber and the total charge created makes proportional counters useful for charged particle spectroscopy. By measuring the total charge (time integral of the electric current) between the electrodes, we can determine the particle's kinetic energy because the number of ion pairs created by the incident ionizing charged particle is proportional to its energy. The energy resolution of a proportional counter, however, is limited because both the initial ionization event and the subsequent 'multiplication' event are subject to statistical fluctuations characterised by a standard deviation equal to the square root of the average number formed. However in practice these are not as great as would be predicted due to the effect of the empirical Fano factor which reduces these fluctuations.^[1] In the case of argon, this is experimentally about 0.2.

Photon detection

Proportional counters are also useful for detection of high energy photons, such as gamma-rays, provided these can penetrate the entrance window. They are also used for the detection of X-rays to below 10 Kev energy levels, using thin walled tubes operating at or around atmospheric pressure.

Radioactive contamination detection

Proportional counters are used extensively as large area detectors to check for radioactive contamination on personnel, tools and items of clothing. This is normally in the form of installed instruments because of the difficulties of providing portable gas supplies for hand-held devices. In this particular application they are flat-chambered multi-wire detectors for alpha and beta detection. They have a large area detection window made from such as metallised mylar to form part of the cathode, and an anode wire routed in a convoluted manner to intersperse fully within the gas fill area of the detector. These detectors are able to discriminate between alpha and beta radiation and have a high efficiency for beta, but lower for alpha. The efficiency reduction for alpha is due to the attenuation effect of the entry window, though distance from the surface being checked also has a significant effect.

They operate at very slight positive pressure above ambient atmospheric pressure. The gas can be sealed in the chamber, or can be changed continuously, in which case they are known as "gas-flow proportional counters". Gas flow types have the advantage that they will tolerate small holes in the mylar screen which can occur in use, but they do require a continuous gas supply.

Guidance on application use

In the United Kingdom the HSE has issued a user guidance note on selecting the correct radiation measurement instrument for the application concerned [1]. This covers all radiation instrument technologies, and is a useful comparative guide to the use of proportional counters.

External articles

Patents

U.S. Patent 3,092,747, S. Fine, "Proportional counter"
U.S. Patent 2,499,830, E. W. Molloy, "Air proportional counter"

References

Glenn F Knoll. Radiation Detection and Measurement, third edition 2000. John Wiley and sons, ISBN 0-471-07338-5.
G.Charpak and F.Sauli; Sauli, F (1984). "High-resolution Electronic Particle Detectors". Annual review of Nuclear Science (Annual Reviews Inc.) 34 (1): 285–350. Bibcode 1984ARNPS..34..285C. doi:10.1146/annurev.ns.34.120184.001441.
E. Mathieson, Induced charge distributions in proportional detectors, http://www.inst.bnl.gov/programs/gasnobledet/publications/Mathieson's_Book.pdf

^ ^a ^b Glenn F Knoll. Radiation Detection and Measurement, third edition 2000. John Wiley and sons, ISBN 0-471-07338-5.

UpToDate Contents

全文を閲覧するには購読必要です。 To read the full text you will need to subscribe.

1. 自動血液分析装置 automated hematology instrumentation
2. 生物統計学および疫学に関する一般用語集 glossary of common biostatistical and epidemiological terms
3. 体重減少がみられる患者に対するアプローチ approach to the patient with weight loss
4. 血小板機能検査 platelet function testing
5. 酸関連疾患治療のためのプロトンポンプ阻害剤の概要および比較 overview and comparison of the proton pump inhibitors for the treatment of acid related disorders

English Journal

Measurement of the (225)Ac half-life.

Pommé S, Marouli M, Suliman G, Dikmen H, Van Ammel R, Jobbágy V, Dirican A, Stroh H, Paepen J, Bruchertseifer F, Apostolidis C, Morgenstern A.SourceEuropean Commission, Joint Research Centre, Institute for Reference Materials and Measurements, Retieseweg 111, B-2440 Geel, Belgium. Electronic address: stefaan.pomme@ec.europa.eu.
Applied radiation and isotopes : including data, instrumentation and methods for use in agriculture, industry and medicine.Appl Radiat Isot.2012 Nov;70(11):2608-14. doi: 10.1016/j.apradiso.2012.07.014. Epub 2012 Jul 25.
The (225)Ac half-life was determined by measuring the activity of (225)Ac sources as a function of time, using various detection techniques: α-particle counting with a planar silicon detector at a defined small solid angle and in a nearly-2π geometry, 4πα+β counting with a windowless CsI sandwi
PMID 22940415

Higher dietary lycopene intake is associated with longer cardiac event-free survival in patients with heart failure.

Biddle M, Moser D, Song EK, Heo S, Payne-Emerson H, Dunbar SB, Pressler S, Lennie T.SourceCollege of Nursing, University of Kentucky, USA.
European journal of cardiovascular nursing : journal of the Working Group on Cardiovascular Nursing of the European Society of Cardiology.Eur J Cardiovasc Nurs.2012 Oct 16. [Epub ahead of print]
BACKGROUND: The antioxidant lycopene may be beneficial for patients with heart failure (HF). Processed tomato products are a major source of lycopene, although they are also high in sodium. Increased sodium intake may counter the positive antioxidant effect of lycopene.METHODS: This was a prospectiv
PMID 23076979