EP0013235B1 - Appareil multiplicateur d'électrons à champ magnétique axial - Google Patents

Appareil multiplicateur d'électrons à champ magnétique axial Download PDF

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Publication number
EP0013235B1
EP0013235B1 EP79401057A EP79401057A EP0013235B1 EP 0013235 B1 EP0013235 B1 EP 0013235B1 EP 79401057 A EP79401057 A EP 79401057A EP 79401057 A EP79401057 A EP 79401057A EP 0013235 B1 EP0013235 B1 EP 0013235B1
Authority
EP
European Patent Office
Prior art keywords
dynode
electron
fact
principal axis
electron multiplier
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.)
Expired
Application number
EP79401057A
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German (de)
English (en)
French (fr)
Other versions
EP0013235A1 (fr
Inventor
Kei-Ichi Kuroda
Daniel Sillou
Fujio Takeuchi
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.)
Bpifrance Financement SA
Original Assignee
Agence National de Valorisation de la Recherche ANVAR
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Filing date
Publication date
Application filed by Agence National de Valorisation de la Recherche ANVAR filed Critical Agence National de Valorisation de la Recherche ANVAR
Priority to AT79401057T priority Critical patent/ATE6711T1/de
Publication of EP0013235A1 publication Critical patent/EP0013235A1/fr
Application granted granted Critical
Publication of EP0013235B1 publication Critical patent/EP0013235B1/fr
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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
    • H01J43/18—Electrode arrangements using essentially more than one dynode
    • H01J43/22—Dynodes consisting of electron-permeable material, e.g. foil, grid, tube, venetian blind
    • 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
    • H01J43/14—Control of electron beam by magnetic field

Definitions

  • the present invention relates to electron multipliers, and more particularly to photomultiplier tubes.
  • electron multiplier devices conventionally comprise, in a tubular vacuum enclosure, first one or more electrodes forming a cathode and directed source of electrons, then a series of electrodes capable of secondary emission of electrons, or dynodes, and finally an anode forming an electron collector. These different electrodes are arranged along the main axis of the tube; in operation, they are brought to potentials capable of creating an electric field accelerating the electrons along this same axis.
  • the electron source made of photosensitive material, is called photocathode.
  • dynodes In a type of electron multiplier ("box-type"), the dynodes each comprise a single element, and the dynodes together define a sort of box channeling the electrons, each dynode facing partly the previous one and partly to the next one.
  • box-type type of electron multiplier
  • each dynode is of distributed structure comprising several active elements (ensuring secondary emission), which extend transversely to the main axis of the tube.
  • each dynode is made up of rectangular strips parallel to each other, the long side of which extends perpendicular to the main axis of the tube, while their short side is inclined on this same axis.
  • such dynodes are said to be “Venetian”, or of the "Persian” type.
  • two consecutive dynodes have an alternating and symmetrical inclination relative to the main axis of the tube.
  • U.S. Patent 2,305,179 describes an electron multiplier apparatus, comprising a vacuum tube which contains multiple stages of distributed structure dynodes capable of secondary reflex electronic emission when struck by charged particles and electron receiving means, means producing an electron accelerating electric field directed substantially along a main axis which passes through the stages of dynodes and going towards the electron receiving means, and means producing a directed magnetic field substantially along the main axis.
  • dynode with a distributed structure capable of secondary reflex electronic emission
  • each dynode consists of a thin grid; the image intensifier described comprises four grids of this kind, and satisfies certain focusing conditions. allowing the device to work despite the presence of a magnetic field. Indeed, magnetic fields are generally considered to be harmful to the proper functioning of high gain electron multipliers.
  • the object of the present invention is to provide an improved electron multiplier, where, in the presence of a magnetic field, a high gain is retained, with improved properties in terms of the rise time (better temporal resolution) and linearity of the output signal.
  • the paths of the secondary electrons form a node at the height of the second level of dynode elements.
  • the dynode stages comprise grids of parallel bars, each grid being substantially perpendicular to the main axis.
  • the small dimension of the bars in the plane perpendicular to the main axis is less than about 1 mm, and the distance between two adjacent bars is at least equal to their small dimension. This jointly improves the spatial resolution and the gain. It is then desirable, although not absolutely necessary, for the electric field to be greater than 200 V / cm, and for the magnetic field to be greater than 0.005 Tesla. In the preferred embodiments of the invention, the small size of the bars is 0.5 mm approximately and the electric field and the magnetic field are chosen correlatively with one another between approximately 400 and 1000 V / cm, and between approximately 0.01 and 0.05 Tesla, respectively.
  • each dynode comprises two grids of bars spaced along the main axis; in each grid the bars are spaced a distance equal to their small dimension; the two grids are offset from each other by a distance equal to their small dimension; and the electric and magnetic fields are correlatively chosen so that a secondary electron emitted by a bar of the first grid always passes statistically between the bars of the second grid (the word statistically means here that a secondary electron nevertheless retains a certain probability - very weak - to reach the bars of the second grid).
  • each dynode comprises n grids of bars spaced along the main axis; in each grid the bars are spaced n times their small dimension; the n grids are successively offset in the same direction by a distance equal to their small dimension each with respect to the previous one; and the electric and magnetic fields are correlatively chosen so that a secondary electron emitted by a bar of a grid on a parallel to the main axis passes statistically on the same parallel substantially at the levels of the following grid and the n-th wire rack.
  • the bars it is also advantageous for the bars to have a cross section symmetrical with respect to a plane parallel to the main axis of the tube and passing through the axis of their largest dimension. This provides better homogeneity of the electric field, and improves spatial resolution.
  • the cross section of the bars is of the isosceles right triangle triangle of hypotenuse directed downstream of the electronic trajectories, of the circylar kind, or of the flat rectangle kind of predetermined inclination on the main axis, the bars then being slats.
  • other types of cross section can be envisaged.
  • the main application studied was that of photo-multipliers, but the invention generally applies to any type of electron multiplier tube whose dynodes, with distributed structure, are capable of secondary reflex emission.
  • the electron emitting and receiving surfaces which surround these dynodes can take different forms.
  • the electron-emitting surface can be an electron-emitting electrode, cathode or photocathode, or a surface transparent to electrons of external origin.
  • the electron receiving surface can be a divided anode with multiple connections, an electroluminescent surface or a mosaic surface which can be analyzed by electron beam, as will be seen below.
  • FIG. 1 is a schematic sectional view of a conventional photomultiplier tube with Venetian dynodes.
  • a photocathode 2 is arranged to receive a light beam L.
  • this cathode reacts to each photon by emitting a primary electron, channeled by an electrode 3.
  • the primary electrons are directed towards a series of 10 dynodes, referenced 4 to 13, and followed by an anode 14.
  • the electrodes are brought to potentials capable of creating an electric field, accelerating the electrons from the cathode towards the anode, that is to say in the direction of the axis of the tube.
  • Each dynode, of distributed structure comprises a plurality of parallel lamellae and inclined which extend perpendicular to the plane of Figure 1, and extend vertically in the plane of Figure 1.
  • the slats are rectangular, 30 mm long and 3 mm wide; their short side is inclined at 45 ° to the main axis of the tube, the direction of inclination being alternated from one dynode to another.
  • the surface of the dynodes is made of material capable of secondary electronic emission, that is to say that, struck by an electron, each dynode will emit several secondary electrons on the side where the primary electron arrived. And the secondary electrons are in turn accelerated and led by the electric field to the next dynode.
  • Figure 2 very schematically illustrates this process, and shows how, for a photon arriving at A on the photo-cathode, the anode receives electrons on a rather large surface denoted D.
  • a dark enclosure 30 has an internal partition 31 x 10 supporting a converging lens 32. and on the other side thereof are housed in the enclosure a photodiode 35 (point source of 0.5 mm) and a photomultiplier tube 36.
  • the photodiode is movable in a plane which is the conjugate with respect to the lens of the plane of the photocathode 37 of the tube 36.
  • the tube comprises several stages of dynodes 34 and an anode 33.
  • the tube 36 is for example the EMI 6262 model, conventionally polarized with a high voltage of 1500 Volts.
  • a coil 39 produces a magnetic field oriented along the main axis 38 of the tube, for example downwards (the direction of the magnetic field has proven to be of little importance so far).
  • FIG. 4 illustrates on the ordinate the output signal of the tube on a logarithmic scale, as a function of the magnetic field applied, plotted linearly on the abscissa.
  • the photodiode was placed in two positions corresponding to the two edges of one of the strips constituting the dynodes.
  • the points marked »+ « and » 0 correspond respectively to the lower and upper edges of the coverslip.
  • the gain is G o ;
  • the gain decreases, and the two points »+ « and »O « separate more and more.
  • the inventors estimated that the value of 0.003 Tesla corresponds to a radius of curvature of the electronic trajectories in the magnetic field of the order of magnitude of the width of the lamellae (3 mm).
  • the B field exceeds 0.003 Tesla, the radius of curvature of the trajectory of a secondary electron emitted by a dynode is small, and the electron is likely to be recaptured by the coverslip, hence the rapid decrease in gain with the magnetic field.
  • the B field is less than 0.003 Tesla, the electron has the greatest chance of gaining the next dynode, hence the substantially constant gain.
  • FIG. 5 illustrates, for a magnetic field of 0.012 Tesla, the output signal of the tube plotted on the ordinate and on a logarithmic scale, as a function of the position of the light point on the cathode, plotted linearly on the abscissa.
  • This figure shows that the gain varies as a function of the position of the light source, and that the shape of the gain reflects the lamellar structure of the dynodes.
  • the inventors have also observed a channeling of the electronic trajectories autor of the axis of the field B. If we return to FIG. 3, the domain D becomes all the smaller as the field B is higher. Again, this is due to the radius of curvature imposed on the electronic trajectories by the magnetic field. This results in the possibility of locating at the level of the anode the origin A of the primary electron, by using for example a fractional or multi-anode anode.
  • the localization effect of the magnetic field is acquired using the electron multiplier tube arranged according to FIG. 3, which retains real multiplying properties, despite a gain much less than the value G o at null field. However, the tube is then unusable in practice, because of its very low gain.
  • the simulation took into account the geometrical configuration of the tube, the value of the potentials between electrodes, the experimental data on the secondary emission of the dynodes, as well as the accessory effects. such as edge loss and space charge.
  • each dynode here comprises two levels.
  • the dynode D n - 1 comprises the levels 61 and 62.
  • the level 61 comprises a series of strips or rather of elongated bars whose section is an isosceles right triangle with a basic 0.5 mm.
  • the base is perpendicular to the main axis of the tube, and exposed to the next dynode.
  • the free space between the vertices of the bases of two adjacent bars is also 0.5 mm.
  • the second level 62 placed 2.5 mm from the first, is constituted in the same way, but its bars are aligned on the free spaces between those of the previous floor, so that seen from above the whole of the dynode constitutes a structure without free space.
  • the second dynode D n is similar to the first, its first level 63 being offset by 10 mm from level 61.
  • the surfaces active on the plane of the secondary electronic emission are at each level the two surfaces inclined at 45 °, defined by the sides of the right angle of the isosceles right triangle.
  • a voltage of 150 volts is established between the levels 61 and 62, a voltage of 600 volts between the stages 61 and 63, and again a voltage of 150 volts between the stages 63 and 64, the polarization being thus repeated periodically for the set of dynodes.
  • FIG. 7 Another structure, mechanically more complex, is illustrated in FIG. 7.
  • the concept of separate dynodes is diluted in this structure, because the set of dynodes consists of a large number of equidistant levels, such as 71 to 76 which represent them. a part.
  • Each level includes bars identical to those in Figure 6, but separated by a free space of 2.0 mm.
  • the bars of a given level are 0.5 mm apart from those of the previous level, to the left for example.
  • the second level 76 bar is located vertically from the first level 71 bar, from the left.
  • the set of levels 71 to 75 forms an opaque system for an electron beam parallel to the z axis.
  • a dynode stage corresponds to 5 consecutive grids or levels, such as 71 to 75.
  • the pitch between stages is 12.5 mm.
  • a magnetic field of 0.041 Tesla and an increasing potential of 400 Volts per stage, (i.e. an electric field of approximately 400 Volts / cm) such an electron multiplier is likely to reach a spatial resolution (at mid-height of the impact distribution on the anode) of ⁇ 1.5 mm, for a gain of the order of 10 7 .
  • the inventors have observed that the structures of dynodes whose bars have a section symmetrical with respect to the z axis are advantageous, as providing a better homogeneity of the electric field, and thereby a better spatial resolution.
  • FIG. 8 Another structure of dynodes is illustrated in FIG. 8. Like that of FIG. 7, it has levels 81 to 86 of active elements regularly distributed along the axis Oz, and offset successively by a value equal to the small dimension. of these active elements, projected onto the x axis (0.5 mm); here again, the free space between two active elements is 2.0 mm, so that the active elements of level 86 are vertical to those of level 81. But, this time, instead of the bars with triangular section , the active elements are Venetian lamellae, inclined at 45 ° all on the same side, and of which only the face facing upwards is capable of secondary emission. A stage is again made up of 5 adjacent levels of lamellas, and the pitch between stages is 5 mm.
  • the secondary electrons thus produced must pass between the bars of the grid 62 to reach one or the other of the grids 63 and 64, and so on, taking into account the dimensions of the structure geometry. We will then say that the trajectories of the electrons coming from the grid 61 form a knot between the bars of the grid 62.
  • the two nodes are substantially aligned with emission point in the z direction, and the electrons then have the greatest chance of touching the grid 76 or another of the consecutive grids forming the next stage, avoiding the grids 72 to 75.
  • the trajectories are more complex, due to the poorer homogeneity of the electric field, due to the asymmetry of the lamellae with respect to the z axis.
  • the spatial resolution can be all the better as the active elements of the grids are made finer, the electric and magnetic fields then being increased accordingly.
  • the electron multipliers according to the invention have better temporal resolution, than the photo-multipliers of the louver type, their rise time being able to drop to less than 2 nanoseconds (10 to 90% of the current peak ) against about 10 nanoseconds for most conventional Venetian dynode photomultipliers.
  • the invention essentially provides an electron multiplier tube capable of localization, that is to say in which there is a fine correspondence between the points of departure of the electrons on the entry surface of the tube and the points of arrival. electrons on the exit surface of the tube.
  • the finesse of this correspondence is defined by the spatial resolution.
  • the currently preferred application is that of photomultipliers, the input surface then being a photocathode.
  • the invention can however be applied with all kinds of cathodes selectively emitting electrons on their surface (divided cathode for example). It is also possible to inject electrons produced by another source through the entry surface of the tube (electron accelerator for example).
  • the term "electron emitting surface” here covers all of these situations.
  • the exit surface of the tube, or “electron receiving surface” should of course allow selective detection of the electrons according to their point of arrival.
  • the resolution is independent of the statistical fluctuation due to the quantum yield of the photoca thode, since the photoelectron source is common for all adjacent anode fragments.
  • the resolution is therefore practically independent of the light intensity of the source analyzed.
  • the electroluminescent screen analogous to cathode ray tube screens, which allows visual and / or photographic examination.
  • the electron receiving surface can also be produced as in television picture tubes, and include a mosaic of small elements which are charged under the effect of the received electrons, while a beam of analyzer electrons comes to sweep this surface to read the charge of each element of the mosaic. A sequential signal is thus obtained which, linked to the scanning, defines the spatial distribution of the electrons received. Due to the sequential scanning, this type of receiving surface does not make it possible to fully benefit from the temporal resolution of the tube according to the invention.
  • a photomultiplier according to the invention with a diameter of 100 mm could replace 50 to 100 small conventional photomultipliers with Venetian dynodes by offering excellent spatial resolution ( ⁇ 1.5 mm), a gain that is practically as good, more homogeneous and more linear, and higher time resolution.
  • each dynode stage is made up of several levels, offset between them so as to constitute together a practically opaque structure for the incident electrons.

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  • Electron Tubes For Measurement (AREA)
  • Analysing Materials By The Use Of Radiation (AREA)
  • Measurement Of Radiation (AREA)
  • Microwave Tubes (AREA)
  • Magnetic Resonance Imaging Apparatus (AREA)
  • Common Detailed Techniques For Electron Tubes Or Discharge Tubes (AREA)
  • Electron Sources, Ion Sources (AREA)
EP79401057A 1978-12-22 1979-12-21 Appareil multiplicateur d'électrons à champ magnétique axial Expired EP0013235B1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT79401057T ATE6711T1 (de) 1978-12-22 1979-12-21 Elektronenvervielfachungsvorrichtung mit axialem magnetischem feld.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR7836148 1978-12-22
FR7836148A FR2445018A1 (fr) 1978-12-22 1978-12-22 Tube multiplicateur d'electrons a champ magnetique axial

Publications (2)

Publication Number Publication Date
EP0013235A1 EP0013235A1 (fr) 1980-07-09
EP0013235B1 true EP0013235B1 (fr) 1984-03-14

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EP79401057A Expired EP0013235B1 (fr) 1978-12-22 1979-12-21 Appareil multiplicateur d'électrons à champ magnétique axial

Country Status (6)

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US (1) US4339684A (enExample)
EP (1) EP0013235B1 (enExample)
JP (2) JPS5590047A (enExample)
AT (1) ATE6711T1 (enExample)
DE (1) DE2966814D1 (enExample)
FR (1) FR2445018A1 (enExample)

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2566175B1 (fr) * 1984-05-09 1986-10-10 Anvar Dispositif multiplicateur d'electrons, a localisation par le champ electrique
DE3709298A1 (de) * 1987-03-20 1988-09-29 Kernforschungsz Karlsruhe Micro-sekundaerelektronenvervielfacher und verfahren zu seiner herstellung
US8048439B2 (en) 2003-11-17 2011-11-01 Btg International Ltd. Therapeutic foam
CZ2006315A3 (cs) 2003-11-17 2006-10-11 Btg International Limited Terapeutická pena

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR824648A (fr) * 1936-11-20 1938-02-14 Electrical Res Products Appareil de décharge d'électrons
US2172738A (en) * 1936-02-03 1939-09-12 Cathode ray tube

Family Cites Families (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL56644C (enExample) * 1935-01-08
US2115155A (en) * 1936-10-21 1938-04-26 Rca Corp Electron multiplier
GB483575A (en) * 1936-10-21 1938-04-21 Marconi Wireless Telegraph Co Improvements in or relating to electron discharge device arrangements
US2196278A (en) * 1937-08-31 1940-04-09 Bell Telephone Labor Inc Electron discharge apparatus
GB504927A (en) * 1937-10-28 1939-04-28 James Dwyer Mcgee Improvements in or relating to electron permeable electrodes
GB508106A (en) * 1937-11-24 1939-06-26 Hans Gerhard Lubszynski Improved electron multiplying electrodes in electric discharge apparatus
US2305179A (en) * 1938-05-27 1942-12-15 Emi Ltd Electron multiplier
US2712738A (en) * 1952-01-10 1955-07-12 Linde S Eismaschinen Ag Method for fractionating air by liquefaction and rectification
GB902090A (en) * 1957-11-12 1962-07-25 Emi Ltd Improvements in or relating to electron discharge devices
NL262542A (enExample) * 1959-09-30
GB976619A (en) * 1960-03-05 1964-12-02 Emi Ltd Improvements in or relating to photo-emissive devices
US3197662A (en) * 1960-03-11 1965-07-27 Westinghouse Electric Corp Transmissive spongy secondary emitter
US3191086A (en) * 1960-11-23 1965-06-22 Radames K H Gebel Secondary emission multiplier intensifier image orthicon
GB1470162A (en) * 1973-02-27 1977-04-14 Emi Ltd Electron multiplying arrangements

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2172738A (en) * 1936-02-03 1939-09-12 Cathode ray tube
FR824648A (fr) * 1936-11-20 1938-02-14 Electrical Res Products Appareil de décharge d'électrons

Also Published As

Publication number Publication date
ATE6711T1 (de) 1984-03-15
JPS6324537A (ja) 1988-02-01
FR2445018A1 (fr) 1980-07-18
JPS5590047A (en) 1980-07-08
FR2445018B1 (enExample) 1982-02-26
US4339684A (en) 1982-07-13
EP0013235A1 (fr) 1980-07-09
JPH0413814B2 (enExample) 1992-03-10
DE2966814D1 (en) 1984-04-19
JPH0231457B2 (enExample) 1990-07-13

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