US2147173A - Electron multiplier - Google Patents

Electron multiplier Download PDF

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Publication number
US2147173A
US2147173A US107955A US10795536A US2147173A US 2147173 A US2147173 A US 2147173A US 107955 A US107955 A US 107955A US 10795536 A US10795536 A US 10795536A US 2147173 A US2147173 A US 2147173A
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United States
Prior art keywords
electrodes
electrode
electron
multiplying
electrons
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Expired - Lifetime
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US107955A
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English (en)
Inventor
Edward G Ramberg
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RCA Corp
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RCA Corp
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Filing date
Publication date
Priority to NL51735D priority Critical patent/NL51735C/xx
Application filed by RCA Corp filed Critical RCA Corp
Priority to US107955A priority patent/US2147173A/en
Priority to CH201427D priority patent/CH201427A/de
Application granted granted Critical
Publication of US2147173A publication Critical patent/US2147173A/en
Anticipated expiration legal-status Critical
Expired - Lifetime 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
    • H01J43/18—Electrode arrangements using essentially more than one dynode
    • H01J43/20—Dynodes consisting of sheet material, e.g. plane, bent

Definitions

  • This invention relates to electric discharge devices and particularly to devices of the type wherein amplification of a primary electron stream, such, for example, as is emitted from a thermionic cathode or from a. photosensitive surface exposed to light, is accomplished through utilization of the phenomenon of secondary emission.
  • the ratio of the number of secondary electrons to the number of primary electrons will depend, in part, upon the velocity of impact and upon the nature of the electrode surface material upon which the primary electrons impinge. This ratio can be considerably greater than unity. If the secondary electrons, in turn, are caused to impinge with sufiicient velocity upon a further electrode having a suitably treated surface, the ratio of secondary emission. from the second multiplying electrode may also be greater than unity. If the newly liberated electrons are thrown against another emissive surface, the number of electrons may once more be increased.
  • n multiplying electrodes in cascade, for example, an amplification of the original or primary electron current equivalent to the amplification per electrode raised to the nth power, provided only that the electrons from one electrode are focused without substantial numerical diminution upon the next succeeding multiplying or target electrode.
  • Slepian U. S. Patent 1,450,265
  • a magnet suitably positioned exterior the tube, so that, when the magnet and electrodes are suitably energized, electrons which otherwise would be drawn to the accelerating electrodes are caused to travel in trochoidal or cycloidal paths and to fall upon the next adjacent multiplying electrode.
  • electron-multipliers of the described magnetic-type have received wide favor, it may be said generally that the magnet renders the device cumbersome, and further, may introduce disturbing electrical efiects upon associated circuits and apparatus.
  • a principal object, therefore, of the present invention is to provide an efficient electron-multiplier operable without the use of auxiliary magnets, electron-lens systems or interposed auxiliary guiding electrodes.
  • Another object of the invention is to provide an electron-multiplier characterized by an economy of parts and operating potentials.
  • FIG. 1 is a view in perspective of a embodiment of the invention, a portion of the tube envelope being broken away to show the elements more clearly,
  • Fig. 2 is a diagrammatic View of the device of Fig. 1, exemplifying the manner in which the several electrodes are energized when the device is utilized for certain of the purposes to which it is adapted, and
  • Fig. 3 is a diagrammatic view of a grid-controlled, thermionioally actuated electron-multiplier constructed and operated in accordance with the principle of the invention.
  • the present invention contemplates and its practice provides an electron-multiplier of the electrostatic type wherein, by reason of certain correlated spacing and dimensions of the electrodes, and of the potentials to which said electrodes are subjected, the electrons are constrained 5 preferred 35 to follow a predetermined inter-electrode path without substantial losses due to the electrons skipping or missing their targets.
  • an improved electric discharge device within the invention may be constituted by an evacuated container, preferably, though not necessarily, cylindrical, wherein are disposed a plurality of sets of discrete multiplying electrodes, the electrodes lying in spacedapart planes parallel to each other and to the long or major axis of the container.
  • the electrodes constituting each set are spaced from each other a distance substantially equal to three-fourths the length of a single plate measured along the major axis of the container.
  • the opposite sets of electrodes are spaced from each other a distance substantially equal to three-fourths the distance between corresponding points on adjacent electrodes of the same set.
  • the electrodes of one set are preferably arranged in staggered relation with respect to the electrodes of the other set, that is to say, the space between two electrodes of a given set should preferably be directly opposite the center of an electrode of the other set.
  • the electrodes if desired, may be solid metallic plates. It is preferable, however, to form them partly of foraminous material, as such construction facilitates the application of the emissive material during construction of the device.
  • the terminal electrodes i. e., the primary-electron emitter (or cathode) and the collector electrode (or anode), preferably present so much of their surfaces in planes perpendicular to the planes of the other electrodes that the otherwise open ends of the electrode assembly. are substantially closed to ensure a desired distribution of the electrostatic field present when the device is energized.
  • each succeeding electrode, in point of electron travel should preferably be maintained at a potential corresponding respectively to the mathematical series +2V, +3V, +4V, +5V, etc.
  • Fig. 1 shows an electron-multiplier constructed in accordance with the invention and contained in an elongated evacuated tube T.
  • a pair of oppositely-located, parallelly-arrangedstrips M, M of mica or other suitable insulating material project outwardly from the stern S of the tube and constitute a supporting structure for a set of lower electrodes, numbered I, 3, 5 and I, respectively, and a set of upper electrodes which are designated 2, 4 and B, respectively.
  • These electrodes are preferably formed of silver and coated with an alkali metal to render them secondarily emissive.
  • Each electrode is provided with two or more lugs n for attachment to the supporting strips M, and with a conductive rodlike lead, I l to I1, respectively, extending through the stem S to the exterior of the tube.
  • the electrodes are each of the same dimensions, and in the interest of economy, of substantially duplicate construction.
  • the electrodes each have an imperforate surface section a and a foraminous or'gridlike section b.
  • Electrodes 2, 4 and 6 have their surfaces arranged in a common plane with their grid-like surface sections b each directly opposite a solid or imperforate section a of one of the lower electrodes.
  • Section a of electrode l is a photosensitive primary-electron emitting cathode. It is adapted to be actuated by light from an external source L (Fig. 2) positioned to shine through the perforate portion b of electrode 2, opposite thereto.
  • the light supplied by source L may be steady or fluctuating in character.
  • Section b of cathode I is bent in a plane normal to the electron emitting surface a, whereby to effectively close the otherwise open end of the electrode assembly.
  • the outer edges of electrodes I and 2 do not touch.
  • the lower electrode 1, nearest the stem, is the anode; its imperforate portion a extends towards but does not touch electrode 6, and efiectively closes this end of the assembly. It is upon this section a. that the electrons are eventually collected.
  • each of these terminal electrodes I and 1 falls along a line midway between the corresponding edges of the terminal multiplying electrodes 2 and 6, respectively.
  • the electrostatic field adjacent the ends of the assembly will correspond substantially to that obtaining adjacent and between the central electrodes (34), so that the electrons emitted from corresponding pointson the several electrodes will travel similar paths to their respective targets.
  • the electrodes are all of the same dimensions.
  • the common plane of the inner surfaces of electrodes 2, 4 and 6 is spaced from the common plane of the inner surfaces of electrodes 1, 3, 5 and I a distance corresponding substantially to three-fourths the length, measured along the long axis of the tube, of a single electrode.
  • the plates were each substantially one inch square and the planes of their surfaces were spaced
  • the electrodes in each set were separated approximately from the next adjacent electrode in the same set.
  • the electrodes were first assembled upon the mica strips M, M, and the leads H to I! welded to electrodes I to I respectively. The entire assembly was then mounted within the tube T which was then heated and evacuated. After evacuation, oxygen was introduced into the tube at a pressure in the neighborhood of 1 mm. of mercury, and the gas activated to cause oxidization of the silver surfaces of the several electrodes.
  • the residual oxygen was pumped out of the tube and alkali metal, in this case caesium, distilled into it.
  • alkali metal in this case caesium
  • the tube was next baked for about ten minutes at a temperature of 210 C. to cause the alkali metal to combine with the silver oxide, thus giving rise to a highly photo-sensitive and secondarily-emissive surface.
  • the excess caesium was pumped out of the tube. The tube was then sealed off.
  • the potential distribution among the electrodes may be expressed by the mathematical series IV, 2V, 3V, 4V, 5V, 6V, etc., where IV is the potential drop between the primary electron source and the first target electrode, and 2V, 3V, V, etc., represent the potential drop b tween the respective 1 succeeding electrodes, in point of electron travel, and said source.
  • the oathode I may be connected to the negative terminalof a source of unidirectional potential, exemplified in the drawing by a resistor R and the first multiplying electrode, i. e., the electrode 2, whose surface is opposite the photo-sensitive cathode, connected to a point IV somewhat more positive.
  • the other electrodes 3 to 1, in the order of their numbers, are shown connected to successively more positive points, 2V to 6V, respectively, on the resistor.
  • the reference characters IV, 2V, 3V, 4V, etc., given to the several points on resistor R, will be understood to indicate that the voltage drop between a given electrode and the cathode is the designated whole number multiple of the voltage drop existing between the cathode I and the first multiplying electrode 2.
  • the drop between electrodes 3 and I should be 200 volts, that between electrodes 4 and I, 300 volts.
  • photo-electrons will be emitted in a quantity determined by the instantaneous intensity of the light beam. These photo-electrons will be accelerated toward the upper electrode 2 and because of the described correlation between their size, position and applied voltages will impinge upon the imperforate portion 2a of this first multiplying electrode 2.
  • the photo-electrons striking electrode 2 will cause the emission of secondary electrons; the number of secondary electrons emitted is dependent, in part, upon the magnitude of the potential difference between it and the cathode.
  • the next electrode, in point of electron travel is the second lower electrode 3.
  • the trajectory of secondaryelectrons from section 2a of the first multiplying electrode is such that they impinge upon section 3a of the second multiplying electrode 3.
  • a multiplication by reason of secondary emission, is secured and this process is repeated in any number of stages until the amplified stream of secondary electrons is collected by the solid upright portion of a of the output electrode I and caused to flow in a utilization circuit exemplified in the drawing by the resistor r included between the output electrode TI and the positive terminal 6V of the potential divider.
  • a thermionic primary electron source instead of a photo-electric source, may be employed, if desired, for rendering the device capable of uses to which well-known thermionic tubes are put.
  • a controllable electron source is substituted for the photo-sensitive section a of electrode I of Figs. 1 and 2.
  • the container '1 is provided with a depending neck portion t which supports a virtual source of electrons in the plane of the lower multiplying electrodes 3 and 5.
  • the electron source may be constituted by a metallic thimble 2!, the upper end of which has a layer of electron emissive oxides 22.
  • the thimble is completely surrounded and shielded by a cylindrical metallic grid structure 23 which terminates in a perforated cap 24.
  • the upper face of the cap lies in the plane of the multiplying electrodes 3 and 5, and, preferably, the perforation therein is coaxial with the emitting portion of the cathode, and is covered by a fine screen 25 to which it is electrically connected.
  • the grid structure 25, when supplied with properpotentials, either direct or fluctuating, serves tocontrol the -emis sion from the thermionic cathode in the same way as emission from the photo-sensitive cathode I in the device of Figs. 1 and 2 is caused to be controlled by variations in the light impinging thereon.
  • any desired input circuit elements may be connected between the grid and the cathode of the tube, exemplified in the drawing by an input resistor 26, a grid biasing potential source 21 and a potential divider 23.
  • the external potential-dividing device exemplified in the drawing by the resistor B. may be dispensed with, if desired, by the provision of individual resistors connecting adjacent electrodes in the same plane.
  • Such resistors may be quite small and, consequently, they may be built into the electrode assembly itself, for instance in the manner described in copending application Serial No. 48,982 to Zworykin and Massa.
  • An electric discharge device comprising an evacuated tube having a major axis, an anode and a cathode mounted in said tube, and a plurality of sets of multiplying electrodes mounted in staggered relation in spaced parallel planes on opposite sides of said major axis intermediate said cathode and anode, said multiplying electrodes each having substantially the same length measured along said major axis, the distance between the planes of the electrodes of each set being substantially equal to three-quarters of the length of a single of said multiplying electrodes.
  • An electron multiplier comprising a bi-part electrode constituted of a continuous surface partly of grid-like and partly of imperforate construction, said imperforate surface section being electron-emissive, and a second electrode of duplicate construction mounted in a plane parallel to said first-mentioned electrode and with its imperforate surface section accessible to electrons from said first-mentioned electrode,
  • An electron multiplier comprising a plurality of sets of opposed electrodes mounted on opposite sides of a common axis, electrode lead for establishing an electrostatic field between said opposed electrodes, and means constituting a portion of a terminal electrode substantially enclosing an otherwise open terminal end of said electrode assembly for ensuring a desired distribution of said electrostatic field.
  • terminal electrode is an electron-emitting cathode.
  • terminal electrode is an electron-collecting anode.
  • each of the terminal ends of said electrode assembly is enclosed by a portion of a terminal electrode.
  • An electron multiplier comprising a cathode, an anode, and a plurality of sets of multiplying electrodes mounted in spaced relation on opposite sides of an axis which extends between said cathode and anode, the distance between said sets of multiplying electrodes measured across said axis being substantially equal to three-quarters of the distance between corresponding points on adjacent electrodes on the same set, the electrodes of one set being ofiset in the anode direction from the electrodes of another set.
  • An electron-multiplier comprising a cathode, an anode and a plurality of sets of multiplying electrodes mounted in staggered relation on opposite sides of an axis which extends between said cathode and anode, said multiplying electrodes each having substantially the same surface dimension measured along said axis, the distance between said opposed sets of multiplying electrodes as measured along a line substantially normal to said axis being less than the said surface dimension of said multiplying electrodes.

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  • Image-Pickup Tubes, Image-Amplification Tubes, And Storage Tubes (AREA)
US107955A 1936-10-28 1936-10-28 Electron multiplier Expired - Lifetime US2147173A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
NL51735D NL51735C (en:Method) 1936-10-28
US107955A US2147173A (en) 1936-10-28 1936-10-28 Electron multiplier
CH201427D CH201427A (de) 1936-10-28 1937-10-26 Elektronenvervielfachungsröhre.

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US107955A US2147173A (en) 1936-10-28 1936-10-28 Electron multiplier

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US2147173A true US2147173A (en) 1939-02-14

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CH (1) CH201427A (en:Method)
NL (1) NL51735C (en:Method)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2836360A (en) * 1954-12-20 1958-05-27 Bendix Aviat Corp Pulse counter

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2836360A (en) * 1954-12-20 1958-05-27 Bendix Aviat Corp Pulse counter

Also Published As

Publication number Publication date
NL51735C (en:Method)
CH201427A (de) 1938-11-30

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