An electron multiplier is a vacuum-tube structure that multiplies incident charges.[1] In a process called secondary emission, a single electron can, when bombarded on secondary-emissive material, induce emission of roughly 1 to 3 electrons. If an electric potential is applied between this metal plate and yet another, the emitted electrons will accelerate to the next metal plate and induce secondary emission of still more electrons. This can be repeated a number of times, resulting in a large shower of electrons all collected by a metal anode, all having been triggered by just one.
Contrasting differences between discrete and continuous electron multipliers.
In 1930, Russian physicist Leonid Aleksandrovitch Kubetsky proposed a device which used photocathodes combined with dynodes, or secondary electron emitters, in a single tube to remove secondary electrons by increasing the electric potential through the device. The electron multiplier can use any number of dynodes in total, which use a coefficient, σ, and created a gain of σn where n is the number of emitters.[2]
Discrete dynodeedit
Secondary electron emission begins when one electron hits a dynode inside a vacuum chamber and ejects electrons that cascade onto more dynodes and repeats the process over again. The dynodes are set up so that each time an electron hits the next one it will have an increase of about 100 electron Volts greater than the last dynode. Some advantages of using this include a response time in the picoseconds, a high sensitivity, and an electron gain of about 108 electrons.[3]
A discrete electron multiplier
Continuous dynodeedit
A continuous dynode system uses a horn-shaped funnel of glass coated with a thin film of semiconducting materials. The electrodes have increasing resistance to allow secondary emission. Continuous dynodes use a negative high voltage in the wider end and goes to a positive near ground at the narrow end. The first device of this kind was called a Channel Electron Multiplier (CEM). CEMs required 2-4 kilovolts in order to achieve a gain of 106 electrons.
Continuous-dynode electron multiplier
Microchannel plateedit
Another geometry of continuous-dynode electron multiplier is called the microchannel plate (MCP).[4][5] It may be considered a 2-dimensional parallel array of very small continuous-dynode electron multipliers, built together and powered in parallel. Each microchannel is generally parallel-walled, not tapered or funnel-like. MCPs are constructed from lead glass and carry a resistance of 109 Ω between each electrode. Each channel has a diameter of 10-100 μm. The electron gain for one microchannel plate can be around 104-107 electrons.[5]
Microchannel plate with breakdown
Applicationsedit
Instrumentsedit
In mass spectrometry electron multipliers are often used as a detector of ions that have been separated by a mass analyzer of some sort. They can be the continuous-dynode type and may have a curved horn-like funnel shape or can have discrete dynodes as in a photomultiplier. Continuous dynode electron multipliers are also used in NASA missions and are coupled to a gas chromatography mass spectrometer (GC-MS) which allows scientists to determine the amount and types of gasses present on Titan, Saturn's largest moon.[6]
Night-visionedit
Microchannel plates are also used in night-vision goggles. As electrons hit the millions of channels, they release thousands of secondary electrons. These electrons then hit a phosphor screen where they are amplified and converted back into light. The resulting image patterns the original and allows for better vision in the dark, while only using a small battery pack to provide a voltage for the MCP.[7]
^Allen, James S. (1947), "An Improved Electron Multiplier Particle Counter", Review of Scientific Instruments, 18 (10): 739–749, Bibcode:1947RScI...18..739A, doi:10.1063/1.1740838.
^Lubsandorzhiev, B.K. (ed.). On the history of photomultiplier tube invention(PDF). CERN. Institute for Nuclear Research of RAS: CERN.
^ Tao, S., Chan, H., & van der Graaf, H. (2016). Secondary Electron Emission Materials for Transmission Dynodes in Novel Photomultipliers: A Review. Materials, 9(12), 1017. https://doi.org/10.3390/ma9121017
^Burroughs, E. G. (1969), "Collection Efficiency of Continuous Dynode Electron Multiple Arrays", Review of Scientific Instruments, 40 (1): 35–37, Bibcode:1969RScI...40...35B, doi:10.1063/1.1683743
^ abWiza, Joseph L. (1979), "Microchannel plate detectors", Nuclear Instruments and Methods, 162 (1–3): 587–601, Bibcode:1979NucIM.162..587L, CiteSeerX10.1.1.119.933, doi:10.1016/0029-554X(79)90734-1.
^Montoro, Harry. "Image Intensification: The Technology of Night Vision". Photonics.
External linksedit
How Discrete Dynode Electron Multipliers work
May 08, 2024
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An electron multiplier is a vacuum tube structure that multiplies incident charges 1 In a process called secondary emission a single electron can when bombarded on secondary emissive material induce emission of roughly 1 to 3 electrons If an electric potential is applied between this metal plate and yet another the emitted electrons will accelerate to the next metal plate and induce secondary emission of still more electrons This can be repeated a number of times resulting in a large shower of electrons all collected by a metal anode all having been triggered by just one Contrasting differences between discrete and continuous electron multipliers Contents 1 History 2 Discrete dynode 3 Continuous dynode 4 Microchannel plate 5 Applications 5 1 Instruments 5 2 Night vision 6 See also 7 References 8 External linksHistory editIn 1930 Russian physicist Leonid Aleksandrovitch Kubetsky proposed a device which used photocathodes combined with dynodes or secondary electron emitters in a single tube to remove secondary electrons by increasing the electric potential through the device The electron multiplier can use any number of dynodes in total which use a coefficient s and created a gain of sn where n is the number of emitters 2 Discrete dynode editSecondary electron emission begins when one electron hits a dynode inside a vacuum chamber and ejects electrons that cascade onto more dynodes and repeats the process over again The dynodes are set up so that each time an electron hits the next one it will have an increase of about 100 electron Volts greater than the last dynode Some advantages of using this include a response time in the picoseconds a high sensitivity and an electron gain of about 108 electrons 3 nbsp A discrete electron multiplierContinuous dynode editA continuous dynode system uses a horn shaped funnel of glass coated with a thin film of semiconducting materials The electrodes have increasing resistance to allow secondary emission Continuous dynodes use a negative high voltage in the wider end and goes to a positive near ground at the narrow end The first device of this kind was called a Channel Electron Multiplier CEM CEMs required 2 4 kilovolts in order to achieve a gain of 106 electrons nbsp Continuous dynode electron multiplierMicrochannel plate editAnother geometry of continuous dynode electron multiplier is called the microchannel plate MCP 4 5 It may be considered a 2 dimensional parallel array of very small continuous dynode electron multipliers built together and powered in parallel Each microchannel is generally parallel walled not tapered or funnel like MCPs are constructed from lead glass and carry a resistance of 109 W between each electrode Each channel has a diameter of 10 100 mm The electron gain for one microchannel plate can be around 104 107 electrons 5 nbsp Microchannel plate with breakdownApplications editInstruments edit In mass spectrometry electron multipliers are often used as a detector of ions that have been separated by a mass analyzer of some sort They can be the continuous dynode type and may have a curved horn like funnel shape or can have discrete dynodes as in a photomultiplier Continuous dynode electron multipliers are also used in NASA missions and are coupled to a gas chromatography mass spectrometer GC MS which allows scientists to determine the amount and types of gasses present on Titan Saturn s largest moon 6 Night vision edit Microchannel plates are also used in night vision goggles As electrons hit the millions of channels they release thousands of secondary electrons These electrons then hit a phosphor screen where they are amplified and converted back into light The resulting image patterns the original and allows for better vision in the dark while only using a small battery pack to provide a voltage for the MCP 7 See also editFaraday cup Daly detector Phototube Photo multiplier tube Scintillation counter Lucas cell Zoltan Lajos Bay developer References edit Allen James S 1947 An Improved Electron Multiplier Particle Counter Review of Scientific Instruments 18 10 739 749 Bibcode 1947RScI 18 739A doi 10 1063 1 1740838 Lubsandorzhiev B K ed On the history of photomultiplier tube invention PDF CERN Institute for Nuclear Research of RAS CERN Tao S Chan H amp van der Graaf H 2016 Secondary Electron Emission Materials for Transmission Dynodes in Novel Photomultipliers A Review Materials 9 12 1017 https doi org 10 3390 ma9121017 Burroughs E G 1969 Collection Efficiency of Continuous Dynode Electron Multiple Arrays Review of Scientific Instruments 40 1 35 37 Bibcode 1969RScI 40 35B doi 10 1063 1 1683743 a b Wiza Joseph L 1979 Microchannel plate detectors Nuclear Instruments and Methods 162 1 3 587 601 Bibcode 1979NucIM 162 587L CiteSeerX 10 1 1 119 933 doi 10 1016 0029 554X 79 90734 1 Mahaffy Paul Mass Spectrometer Detector NASA Montoro Harry Image Intensification The Technology of Night Vision Photonics External links editOlympus Tutorial How Discrete Dynode Electron Multipliers work Retrieved from https en wikipedia org w index php title Electron multiplier amp oldid 1169670769, wikipedia, wiki, book, books, library,
