US3239709A - Electron multiplier having electrostatic field shaping electrodes - Google Patents

Electron multiplier having electrostatic field shaping electrodes Download PDF

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Publication number
US3239709A
US3239709A US205359A US20535962A US3239709A US 3239709 A US3239709 A US 3239709A US 205359 A US205359 A US 205359A US 20535962 A US20535962 A US 20535962A US 3239709 A US3239709 A US 3239709A
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United States
Prior art keywords
coating
envelope
field
resistive
electron
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Expired - Lifetime
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US205359A
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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 BE633901D priority Critical patent/BE633901A/xx
Priority to NL294533D priority patent/NL294533A/xx
Application filed by RCA Corp filed Critical RCA Corp
Priority to US205359A priority patent/US3239709A/en
Priority to GB23105/63A priority patent/GB1033935A/en
Priority to DER35403A priority patent/DE1238579B/de
Priority to FR939099A priority patent/FR1361071A/fr
Application granted granted Critical
Publication of US3239709A publication Critical patent/US3239709A/en
Anticipated expiration legal-status Critical
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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
    • H01J43/24—Dynodes having potential gradient along their surfaces

Definitions

  • One class of electron multiplier tube which has found wide commercial interest is a photosensitive electron multiplier or photomultiplier tube.
  • This class of photomultiplier tube includes types sensitive to visible light and types responsive to radiant energy of other wavelengths, e.g. ultraviolet.
  • One type of photomultiplier tube comprises a photocat-hode with one or more secondary electron emissive electrodes, or dynodes, spaced from the photocathode.
  • the first dynode is of particular configuration so that the primary electrons will travel from the photocathode to the first dynode where they will be multiplied.
  • the balance of the dynodes are also of particular configurations so that the multiplied electrons from the first dynode will, in turn, travel from the first dynode to the second dynode to be multiplied further. This process is repeated until the multiplied electrons are collected on a collector electrode.
  • Another type of photomultiplier tube is one in which two parallel insulating plates are provided within an en velope. Each of the plates has aresistive, secondary emissive, coating thereon.
  • a potential difierence is applied between the opposite ends of each of the resistive coatings, and when the plates are pulsed to opposite polarities, at a frequency corresponding, e.g. to half the reciprocal transit time between them, i.e. one positive and one negative at one instance, and then the reverse, electrons go from one plate to the other because of the opposite polarity pulsing. The electrons travel down the length of the plates because of the potential gradient established between the ends of the resistive coatings.
  • Another type of known photomultiplier tube is one in which a pair of oppositely disposed parallel plates is provided, each having a resistive coating thereon.
  • a potential from one end of each plate to the other is applied, and the potential is such that the potential of any area of one plate is consistently more positive than the potential of the opposite area of the other plate, the electrons travel from one end to the other of the less positive plate if a magnetic field is applied parallel to the surfaces of the plates and at right angles to the potential gradient established on them, with electron multiplication taking place at successive impacts on the plate.
  • known photomultiplier tubes employ either special configurations of the various dynodes, the use of alternate polarity potentials, or the use of a magnetic field, or some combination of these.
  • a substantially circularly cylindrical, insulating support having a resistive, secondary emissive coating deposited thereon.
  • two field-shaping electrodes extending in a plane from the inner surface of the cylindrical support substantially to the axis of symmetry of the cylindrical support.
  • FIG. 1 is a top sectional view of a photomultiplier tube made in accordance with this invention
  • FIG. 2 is an elevational view taken along line 22 of FIG. 1;
  • FIGS. 3, 4, and 5 are top sectional views of other embodiments of multiplier tubes made in accordance with this invention.
  • FIG. 6 is a sectional view of another embodiment of the secondary emissive surface in accordance with this invention.
  • the multiplier tube 10 comprises a substantially cylindrical envelope 12 which may be made of a material such as glass.
  • the secondary electron emissive coating 14 is a resistive coating and should have a surface resistivity of at least 10 ohms. The reason for the minimum resistivity is to limit the amount of power dissipation. Furthermore, the total resistance should be less than the ratio of the voltage applied to the dynode coating, to the desired output current. Thus, 10 ohms is the approximate maximum surface resistivity.
  • the maximum resistivity is determined because the voltage drops across the resistive coating, resulting from current flowing in it, should be larger than the voltage drop which would be produced by the emission current flowing through the resistive coating. Thus, the emission current should not destroy the field distribution.
  • the resistive coating 14 may be both photosensitive and secondary emissive.
  • the coating 14 may comprise a cesium antimonide coating.
  • a method of preparing such a coating may be found in a book by Zworykin and Rarnberg, entitled Photoelectricity, published by Wiley, 1949, e.g., see page 96.
  • Other resistive coatings, which are not photoemissive, such as magnesium oxide on a resistive substrate of tin oxide, which have a high secondary emission factor, may be used.
  • each of electrodes 16 and 18 extends radially inwardly from the envelope wall almost to the central axis of the cylindrical coating 14, and the outer ends of the two electrodes .16 and 18 are respectively adjacent or close to the two ends of the coating 14. It should be noted that an insulated gap 20 exists on the wall of the envelope between the two field shaping electrodes I6 and 18.
  • the resistive coating 14 does not cover the entire inner surface of the envelope Part of the area of one of the field shaping electrodes 16, i.e., the part adjacent to the envelope wall, may be coated with a photoemissive surface 22, assuming that the coating 14 is not photoemissive.
  • the photoemissive surface 22 may be selected for its sensitivity of any particular wavelength of energy and may comprise any suitable, known photocathode. Examples of known photo'- cathodes are the S11 photosurface described in U.S. Patent 2,676,282 to Polkosky issued Apr. 20, 1954, and the multi-alkali photosurface described in U.S. Patent 2,770,561 to Sommer issued Nov. 13, 1956.
  • a still further alternative is to deposit photosensitive material on a short section of the envelope wall 12, adjoining the negative field-shaping elect-rode 16, while the balance of the coating 14 is selected for its secondary emissive properties.
  • a potential difference of the order of one thousand volts to several thousand volts, is maintained, by means of an external power supply 23, between the ends of the resistive coating 14 adjacent to the two field-shaping electrodes 16 and 18.
  • the end of the coating 14 adjacent to the field shaping electrode 16 is made negative, while that adjacent to field shaping electrode 18 is made positive.
  • the negatively biased end of the resistive coating 14 may be electrically connected to the adjacent field-shaping electrode 16, and also to the photoemissive surface 22 in certain embodiments.
  • the positively biased end of the resistive coating 14 terminates close to but spaced from the adjacent field-shaping electrode 18 in the embodiment shown in FIGS. 1 and 2.
  • the electrode 18 functions as an electron collector.
  • a bias voltage is applied, by means of a source 25 which is preferably a direct current source, between the collector and ground through a signal resistance 24.
  • Electrons are emitted from the photoemissive surface 22 when light 26 is incident thereon. As the electrons travel from their point of origin, the electrons are subject to an electric field which, for the indicated shape of the field-shaping plates 16 and 18 and for a uniform surface resistivity of the coating 14, is at all points in a tangential direction.
  • the field is illustrated by the radial equipotential surface lines 28 shown in FIG. 1.
  • the electric field deflects the electrons in a direction along the tube wall toward the positive end of the resistive secondary electron emissive coating 14. Such a path is illustrated by the typical idealized electron paths 30 shown in FIG. 1.
  • the average displacement between the point of origin and the point of impact on the wall is, for a total applied voltage of the order of one thousand volts, approximately /2 radian. Since the coating extends over five radians (i.e. about of the tube circumference) the energy of each impact will be about 100 electron volts. For this energy of impact, every primary electron ejects about four secondary electrons from a good secondary emitting surface. These four secondary electrons travel, on the average, another half radian, toward the collector electrode 18 before they impinge on the surface 14 to produce some sixteen secondary electrons. Under the indicated circumstances there are thus approximately ten stages of secondary electron multiplication resulting in a total current gain of about one million before the electrons reach the collector electrode 16.
  • the gain from the tube will be less if the secondary emission factor of the resistive coating 14 is less than that indicated, i.e. less than four.
  • the gain can be increased by increasing the potential applied between the ends of the resistive coating 14 since this increases both the energy of impact and the number of stages of multiplication.
  • the three external lead-ins required namely to the negative or cathode end of the resistive coating 14, the positive or anode end of the resistive coating 14, and the collector electrode 18, may be brought out of the tube 10 by any conventional vacuum tube base and pin contact arrangement.
  • the lead-ins may be sealed directly through the side of the envelope wall 12.
  • the field-shaping electrodes 16 and 18 are formed as conducting plates or metal sheets, they may be of the form of conductive coatings on insulating plates.
  • the electrode structure is open-ended, its length in the direction of the axis of the tube 10 should be at least equal to the diameter of the structure. The reason for this is to insure that the electric fields, near the central portion of the structure, are adequately defined by the field-shaping electrodes 16 and 18 and the resistive coating 14. When the top and bottom ends of the resistive coating 14 extend to a point close to the axis of the tube 10, i.e. along the top and bottom ends of the inner surface of the envelope in the position shown in FIG. 2, the height of the structure can be substantially less.
  • a tube 40 is provided which differs from the embodiment shown in FIG. 1 in that a fine mesh screen 42 is provided in front of the positive field-shaping electrode 44.
  • the electrode 44 may be connected to the positive end of the resistive secondary emissive coating 14. With a signal resistance and a bias supply V the mesh screen 42 then functions as collector electrode during tube operation.
  • a solid collector electrode 50 is used.
  • the collector electrode 50 is supported in front of a positive field-shaping electrode 52.
  • the positive field-shaping electrode 52 may be connected directly to the positive end of the resistive secondary emissive coating 14.
  • FIG. 5 there is shown a further embodiment of this invention wherein the envelope wall itself is pushed inwardly to form a V-shaped wedge 58.
  • the field-shaping electrodes 60 and 62 are then formed as separate conductive coatings, e.g. conductive tin oxide, on the wedge 58.
  • a photocathode 64 may be deposited adjacent to the negative field shaping electrode 60 and a different material used for the resistive secondary emissive coating 66.
  • FIG. 6 there is shown another embodiment of this invention which comprises a mosaic 70 of minute, conducting, secondary emissive elements deposited on a resistive surface film 72.
  • a secondary emissive mosaic 70 as well as a photo-emissive mosaic, is the conventional mosaic used in an iconoscope type camera tube.
  • Such a mosaic is conventionally made of cesium-activated globules of oxidized silver, in a known manner.
  • the resistive film may, as an alternative, be made of cesium-activated patches of antimony evaporated through a fine mesh.
  • resistive film with a secondary emissive mosaic coating such as that shown in FIG. 6, may be used with any of the structures shown and described in connection with FIGS. 1 through 5.
  • tubes made in accordance with this invention are more efiicient than those operated in a magnetic field.
  • tubes made in accordance with the teachings of this invention are economical to construct and operate.
  • the potential variation along the resistive coating 14 within the structure 10 is given by where is the potential measured with respect to the potential of the cathode, or negative end of coating 14, as zero; 6 is the azimuthal angle measured from the cathode toward the anode, or positive, end of coating 14; and K is potential gradient applied to the resistive coating 14 in terms of volts per radian.
  • the equations of motion of the electrons in this field are given by Here, dots indicate difierentiation with respect to the time t; r is the radial coordinate measured from the tube axis; -e/m is the specific charge of the electron; and z is the longitudinal coordinate, measured parallel to the tube axis.
  • Gain modulation by a magnetic field parallel to the axis The gain of the multiplier can be effectively modulated by immersing it in a solenoid.
  • the field required for this gain modulation would be produced by a coil with about 5 6 ampere turns per inch.
  • a photomultiplier tube comprising:
  • a multiplier tube comprising:
  • each of said field forming electrodes extending radially from a region close to a different end of said coating substantially to the axis of said inner surface;
  • a photomultiplier tube comprising:
  • said envelope including a pair of end members each closing a different end of said elongated tubular envelope
  • each of said field forming electrodes extending radially from said inner surface of said envelope substantially to the axis of said envelope;
  • each of said field for-ming electrodes also extending substantially from one of said end members to the other of said end members;
  • An electron multiplier tube adapted for use Without a magnetic field comprising:

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  • Image-Pickup Tubes, Image-Amplification Tubes, And Storage Tubes (AREA)
  • Electron Tubes For Measurement (AREA)
US205359A 1962-06-26 1962-06-26 Electron multiplier having electrostatic field shaping electrodes Expired - Lifetime US3239709A (en)

Priority Applications (6)

Application Number Priority Date Filing Date Title
BE633901D BE633901A (en, 2012) 1962-06-26
NL294533D NL294533A (en, 2012) 1962-06-26
US205359A US3239709A (en) 1962-06-26 1962-06-26 Electron multiplier having electrostatic field shaping electrodes
GB23105/63A GB1033935A (en) 1962-06-26 1963-06-10 Electron multiplier
DER35403A DE1238579B (de) 1962-06-26 1963-06-11 Elektronenvervielfacher mit einer konkav gekruemmten Flaeche aus einem sekundaeremissionsfaehigen Widerstandsmaterial
FR939099A FR1361071A (fr) 1962-06-26 1963-06-24 Multiplicateurs d'électrons

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US205359A US3239709A (en) 1962-06-26 1962-06-26 Electron multiplier having electrostatic field shaping electrodes

Publications (1)

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US3239709A true US3239709A (en) 1966-03-08

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US205359A Expired - Lifetime US3239709A (en) 1962-06-26 1962-06-26 Electron multiplier having electrostatic field shaping electrodes

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US (1) US3239709A (en, 2012)
BE (1) BE633901A (en, 2012)
DE (1) DE1238579B (en, 2012)
GB (1) GB1033935A (en, 2012)
NL (1) NL294533A (en, 2012)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3445709A (en) * 1967-06-23 1969-05-20 Itt Cylinder with internal photosensitive coating and prism on outer surface for admitting light at an angle to be totally internally reflected
US4604545A (en) * 1980-07-28 1986-08-05 Rca Corporation Photomultiplier tube having a high resistance dynode support spacer anti-hysteresis pattern

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1841033A (en) * 1925-08-20 1932-01-12 Western Electric Co Photo-electric tube
US2141322A (en) * 1935-06-25 1938-12-27 Rca Corp Cascaded secondary electron emitter amplifier
US2185172A (en) * 1936-03-17 1940-01-02 Aeg Electron multiplier
US2198227A (en) * 1938-05-03 1940-04-23 Rca Corp Electron multiplier
US2231676A (en) * 1936-12-05 1941-02-11 Klangfilm Gmbh Electric amplifier
US2285126A (en) * 1939-07-28 1942-06-02 Rca Corp Electron multiplier
US2903595A (en) * 1954-12-24 1959-09-08 Rca Corp Electron multiplier

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CH234444A (de) * 1942-05-15 1944-09-30 Bosch Gmbh Robert Elektronenvervielfacher.

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1841033A (en) * 1925-08-20 1932-01-12 Western Electric Co Photo-electric tube
US2141322A (en) * 1935-06-25 1938-12-27 Rca Corp Cascaded secondary electron emitter amplifier
US2185172A (en) * 1936-03-17 1940-01-02 Aeg Electron multiplier
US2231676A (en) * 1936-12-05 1941-02-11 Klangfilm Gmbh Electric amplifier
US2198227A (en) * 1938-05-03 1940-04-23 Rca Corp Electron multiplier
US2285126A (en) * 1939-07-28 1942-06-02 Rca Corp Electron multiplier
US2903595A (en) * 1954-12-24 1959-09-08 Rca Corp Electron multiplier

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3445709A (en) * 1967-06-23 1969-05-20 Itt Cylinder with internal photosensitive coating and prism on outer surface for admitting light at an angle to be totally internally reflected
US4604545A (en) * 1980-07-28 1986-08-05 Rca Corporation Photomultiplier tube having a high resistance dynode support spacer anti-hysteresis pattern

Also Published As

Publication number Publication date
DE1238579B (de) 1967-04-13
NL294533A (en, 2012)
BE633901A (en, 2012)
GB1033935A (en) 1966-06-22

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