EP2634790A2 - Appareil de multiplication d'électrons - Google Patents

Appareil de multiplication d'électrons Download PDF

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Publication number
EP2634790A2
EP2634790A2 EP13156927.9A EP13156927A EP2634790A2 EP 2634790 A2 EP2634790 A2 EP 2634790A2 EP 13156927 A EP13156927 A EP 13156927A EP 2634790 A2 EP2634790 A2 EP 2634790A2
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EP
European Patent Office
Prior art keywords
electrodes
electrode
anode
electron
wall
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP13156927.9A
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German (de)
English (en)
Other versions
EP2634790A3 (fr
Inventor
Jonathan Ross Howorth
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Photek Ltd
Original Assignee
Photek Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Photek Ltd filed Critical Photek Ltd
Publication of EP2634790A2 publication Critical patent/EP2634790A2/fr
Publication of EP2634790A3 publication Critical patent/EP2634790A3/fr
Withdrawn legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J43/00—Secondary-emission tubes; Electron-multiplier tubes
    • H01J43/04—Electron multipliers
    • H01J43/06—Electrode arrangements
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J43/00—Secondary-emission tubes; Electron-multiplier tubes
    • H01J43/04—Electron multipliers
    • H01J43/28—Vessels, e.g. wall of the tube; Windows; Screens; Suppressing undesired discharges or currents

Definitions

  • This invention relates to electron multiplying apparatus, and to methods of use and manufacture thereof.
  • Electron multipliers are well known in the prior art; electrons are accelerated by a potential difference in an evacuated enclosure and bombard a second electron emissive material, thus releasing many secondary electrons at each collision.
  • a relatively small initial signal - perhaps a single electron generated by the collection of one or a small number of photons - can be multiplied many times to generate a detectable signal.
  • the output of such a device involves the multiplied electrons being incident upon an anode.
  • there is secondary electron emission from the anode which can be a concern when looking for a very fast signal.
  • detecting current from the anode there is a negatively rising pulse as electrons approach and land on the anode followed by a positive going signal as secondary electrons leave the anode. If the secondary electron emission coefficient of the anode is one, then in some circumstances both signals cancel each other. Consequently, it is usual practice to try to suppress secondary electron emission from the anode by coating it with material chosen for this purpose.
  • the electric signal generated by the incident electrons can be measured, and in some cases the position determined.
  • US Patent number 5 686 721 discloses a system where a single high resistance electrode is provided as the output anode, and three electrodes are provided externally to the enclosure capacitively coupled to the output anode. Interpolation of the signals received at each electrode allows the position of the incident electron to be estimated.
  • a disadvantage of such an arrangement is that, in some cases, it is difficult to determine the position of an event such as an incident electron without interpolating the relative charge spreading between several external anode circuits.
  • the spatial resolution is dependent on the thickness of the dielectric wall of the detector which, as discussed above, can be significant for larger detectors.
  • an electron multiplying apparatus comprising:
  • each pair of electrodes will capacitively couple together and so it will be possible to determine the position of the electrons incident on the first electrodes by determining the second electrode on which a signal is generated.
  • the apparatus comprises a layer of secondary emissive material on the first electrodes (which may function as an anode) on the inner surface of the wall, positioned so that electrons emitted by the electron multiplier are incident on the layer.
  • a layer of secondary emissive material on the first electrodes (which may function as an anode) on the inner surface of the wall, positioned so that electrons emitted by the electron multiplier are incident on the layer.
  • the apparatus comprises a metallic grid between the electron multiplier and the first electrodes.
  • the metallic grid may be positioned to collect the electrons generated by the layer of secondary emissive material.
  • the apparatus may comprise a semi-insulating anode joining the first electrodes together.
  • the apparatus may also comprise a voltage source arranged to provide a potential difference between the anode and the electron multiplier, and typically also across the electron multiplier, and between the anode and the metallic grid.
  • Either of the first and second electrodes can be formed of metal or metallic materials.
  • the anode can comprise sapphire and the first electrodes can be formed of silicon.
  • the layer may be formed of diamond, typically polycrystalline diamond.
  • the diamond may be doped, typically with boron; this allows the degree of insulation of the layer to be controlled.
  • the anode can comprise sapphire or borosilicate glass, preferably expansion matched to the wall.
  • the first electrodes can each comprise a metal film, which can be formed by screen printing a metal film or thermal evaporation of a metal film in vacuum.
  • the layer can be formed over the first electrodes by means of a process such as atomic layer deposition of a material having high secondary electron emission, such as Magnesium Oxide (MgO) doped with a small percentage, say around 60%, typically between 50-70%, of Zinc Oxide (ZnO).
  • MgO Magnesium Oxide
  • ZnO Zinc Oxide
  • the apparatus may further comprise a detection circuit for detecting at each second electrode an electric signal generated by the incidence of an electron at the corresponding first electrode.
  • the detection circuit may have a time resolution being the precision with which it can determine the arrival time of the electric signal; the time resolution may be better than or at most 200 picoseconds, and preferably better than or at most 100 picoseconds.
  • the detection circuit may be electrically coupled to each second electrode.
  • the detection circuit may only be electrically coupled to each first electrode via each second electrode. This therefore reduces the need for connections to be made through the wall.
  • the capacitance between each pair of first and second electrodes may be significantly more than the capacitance between any pair of first electrodes, and in particular between adjacent pairs of first electrodes. As such, the capacitance between each pair of first and second electrodes may be in the region of 0.1 to 10 picofarads, typically around 1 to 2 picofarads.
  • the layer, the first electrodes and the anode may be provided in any order on the wall; in a preferred embodiment, the anode can be on the inner surface of the wall, the first electrodes over the anode and the layer over the electrodes, so as to be closest to the incident electrons.
  • the electron multiplier will preferably comprise a microchannel plate.
  • the microchannel plate may be a glass or silicon microchannel plate.
  • a method of manufacturing part of an electron multiplying apparatus comprising applying, to an area of a wall of the apparatus:
  • the electron multiplying apparatus is one in accordance with the first aspect of the invention.
  • the method may further comprise applying a semi-insulating anode to the area.
  • the method may also comprise applying a plurality of second electrodes to an opposing side of the wall to the first electrodes, there being a second electrode for and adjacent to each first electrode.
  • the method may comprise providing a sapphire anode, typically with a layer of silicon thereon.
  • the method may further comprise etching the silicon to form the first electrodes.
  • the method may further comprise growing the layer of secondary emissive material over the etched electrodes, the layer comprising polycrystalline diamond.
  • the method may include the step of doping the polycrystalline diamond, typically with boron. The level of doping can be used to control the degree of insulation of the anode.
  • the method may then comprise the step of joining the anode, first electrodes and layer to the wall; this can be by any suitable means, for example brazing, soldering or by using glass frits. This method is particularly applicable where the wall is formed of alumina ceramic.
  • the step of joining may provide the steps of applying the first electrodes, the layer and the anode.
  • the anode is formed of sapphire or borosilicate glass.
  • the method may comprise the step of applying the first electrodes to the anode, which may be formed as a flat plate made of sapphire or glass etc, typically by screen printing a metal film or thermal evaporation of a metal film.
  • the method may then include the step of applying the layer over the electrodes, typically through atomic layer deposition.
  • the layer may comprise Magnesium Oxide (MgO) doped with Zinc Oxide (ZnO).
  • MgO Magnesium Oxide
  • ZnO Zinc Oxide
  • a method of using an electron multiplying apparatus comprising determining the position of electrons incident on the first electrodes by determining on which second electrodes an electronic signal is received.
  • the apparatus 1 comprising a housing 2 having walls which define an evacuated enclosure 3 which is kept at significantly below atmospheric pressure (typically Ultra High Vacuum, that is less than 100 nanopascals). Within the enclosure 3 there is provided a source of electrons, being a photoelectron conversion layer 4 such as the well known Bialkali photocathode.
  • a photoelectron conversion layer 4 such as the well known Bialkali photocathode.
  • Light 5 incident on the photoelectron conversion layer 4 causes the emission of electrons 6.
  • the microchannel plate is formed of a plurality of narrow glass tubes embedded in a matrix.
  • a power supply 8 external to the enclosure 3 provides a potential difference of around 1000V across the microchannel plate 7.
  • the action of the potential difference on the microchannel plate 7 is to multiply the incident electrons 6, such that for each primary electron 6, many more (typically 100,000) secondary electrons 9 are emitted.
  • the secondary electrons 9 are emitted from the microchannel plate 7 and pass to an output structure 10 on the inside of the wall of the housing 2.
  • This structure 10 comprises a semi-insulating anode 11, connected to the power supply 8 so as to be at a potential difference to the microchannel plate 7, with a plurality of individual conducting first electrodes 12 formed thereover.
  • the shapes of the electrodes can be as desired; some example shapes are shown in Figures 2a and 3a of the accompanying drawings. A grid of such electrodes can then be built up, with the grid spacing being around 5 mm.
  • each first electrode 12 is provided with a corresponding second electrode 14 on the outside of the wall of the housing 2 adjacent to the first electrode 12 (and so also forming a grid).
  • Each pair of first and second electrodes is capacitively coupled together, such that an electron incident on a first electrode 12 will cause an electric signal to be generated at the corresponding second electrode 14.
  • This electric signal is picked up by a detector circuit 15.
  • the detector circuit 15 can determine the location of the electron that caused that signal to be generated on the first electrodes. The position of the photon which caused the original primary electron emission can therefore be estimated.
  • a layer of secondary emissive material 13 is provided over the electrodes. Electrons incident on the structure 10 will first hit the layer 13, in which further secondary electron emission will occur. This amplifies the electron signal externally to the microchannel plate 7, so reducing the space charge within the microchannel plate 7, given that the microchannel plate can only sustain a limited current in terms of amperes per square centimetre of face area. By providing gain after the microchannel plate, higher count rates can be used.
  • the detector circuit 15 can be coupled to the second electrodes by means of a simple electrical contact (be it silver epoxy, springs or so on). There is no need, as far as the detection circuit is concerned, to make any connections through the walls of the housing 2. This reduces the number of through connections that are required, thus making the apparatus much easier to manufacture. Furthermore, there is less cross talk between first electrodes than there would be if a single resistive electrode were to be used.
  • the semi-insulating anode 11 can be formed of sapphire and can be joined to the housing 2 by brazing, soldering or with glass frits.
  • the first electrodes 12 are formed of silicon; silicon-on-sapphire discs of several centimetres in diameter are available commercially. The first electrodes can be formed by etching patterns into the silicon on those discs to define the gaps between the electrodes.
  • the layer 13 can then be formed as a layer of polycrystalline diamond on the silicon electrodes 12 by plasma deposition. The degree of insulation is controllable by boron doping the diamond film during deposition.
  • the semi-insulating anode 11 is made from sapphire or a borosilicate glass chosen to match other manufacturing requirements.
  • An array of first electrode 12 patterns is made by, for example, screen printing a metal film or thermal evaporation of a metal film in vacuum through a metal mask.
  • ALD Atomic Layer Deposition
  • This film could for example be magnesium oxide (MgO) doped with a small percentage of zinc oxide (ZnO).
  • the secondary electron emission of diamond can reach 100 secondary electrons per primary electron, potentially improving the count rate by this same number, but is a relatively more expensive approach than the ALD route.
  • the ALD route achieves a much more modest improvement of about 8:1.
  • the capacitance between each pair of first 12 and second 14 electrodes will be very much more than the capacitance between adjacent first electrodes 12, typically in the region of 1 to 2 picofarads.
  • the second electrodes will typically be 3 to 5 mm in diameter, around 20 mm 2 in area.
  • FIG. 4 of the accompanying drawings shows an electron multiplying apparatus according to a second embodiment of the invention. This functions in much the same way as the apparatus of Figures 1 to 3 , and to that end features that function in the same manner as in the previous embodiment have been given corresponding reference numerals, raised by 50.
  • This embodiment explicitly includes a metallic grid 70, which forms a collector mesh.
  • the metallic grid is connected to the power supply 58.
  • the power supply applies potential differences, so that the various components are at the voltages, relative to an arbitrary zero:

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  • Electron Tubes For Measurement (AREA)
  • Measurement Of Radiation (AREA)
EP13156927.9A 2012-02-29 2013-02-27 Appareil de multiplication d'électrons Withdrawn EP2634790A3 (fr)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GBGB1203561.4A GB201203561D0 (en) 2012-02-29 2012-02-29 Electron multiplying apparatus

Publications (2)

Publication Number Publication Date
EP2634790A2 true EP2634790A2 (fr) 2013-09-04
EP2634790A3 EP2634790A3 (fr) 2015-10-07

Family

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Family Applications (1)

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EP13156927.9A Withdrawn EP2634790A3 (fr) 2012-02-29 2013-02-27 Appareil de multiplication d'électrons

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EP (1) EP2634790A3 (fr)
GB (1) GB201203561D0 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3107115A1 (fr) * 2015-06-19 2016-12-21 Photek Limited Détecteur
US9934952B2 (en) 2015-08-10 2018-04-03 Hamamatsu Photonics K.K. Charged-particle detector and method of controlling the same

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5686721A (en) 1994-08-23 1997-11-11 Litef Gmbh Position-transmitting electromagnetic quanta and particle radiation detector

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2506518A1 (fr) * 1981-05-20 1982-11-26 Labo Electronique Physique Structure multiplicatrice d'electrons comportant un multiplicateur a galettes de microcanaux suivi d'un etage amplificateur a dynode, procede de fabrication et utilisation dans un tube photoelectrique
US5493111A (en) * 1993-07-30 1996-02-20 Litton Systems, Inc. Photomultiplier having cascaded microchannel plates, and method for fabrication
FR2754068B1 (fr) * 1996-10-02 1998-11-27 Charpak Georges Detecteur a gaz de rayonnements ionisants a tres grand taux de comptage
GB2359187A (en) * 2000-02-11 2001-08-15 Kindbrisk Ltd Device and method for two-dimensional detection of particles or electromagnetic radiation
GB2475063A (en) * 2009-11-04 2011-05-11 Univ Leicester Charge detector for photons or particles.

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5686721A (en) 1994-08-23 1997-11-11 Litef Gmbh Position-transmitting electromagnetic quanta and particle radiation detector

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3107115A1 (fr) * 2015-06-19 2016-12-21 Photek Limited Détecteur
GB2539506A (en) * 2015-06-19 2016-12-21 Photek Ltd Detector
US10054696B2 (en) 2015-06-19 2018-08-21 Photek Limited Detector for an electron multiplier
US9934952B2 (en) 2015-08-10 2018-04-03 Hamamatsu Photonics K.K. Charged-particle detector and method of controlling the same

Also Published As

Publication number Publication date
EP2634790A3 (fr) 2015-10-07
GB201203561D0 (en) 2012-04-11

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