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US3321660A - Electron multiplier having resistive secondary emissive surface which is adapted to sustain a potential gradient, whereby successive multiplication is possible - Google Patents

Electron multiplier having resistive secondary emissive surface which is adapted to sustain a potential gradient, whereby successive multiplication is possible Download PDF

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Publication number
US3321660A
US3321660A US197467A US19746762A US3321660A US 3321660 A US3321660 A US 3321660A US 197467 A US197467 A US 197467A US 19746762 A US19746762 A US 19746762A US 3321660 A US3321660 A US 3321660A
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United States
Prior art keywords
coating
emissive
tube
envelope
electrons
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Expired - Lifetime
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US197467A
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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 BE632654D priority Critical patent/BE632654A/xx
Priority to NL293150D priority patent/NL293150A/xx
Application filed by RCA Corp filed Critical RCA Corp
Priority to US197467A priority patent/US3321660A/en
Priority to GB17010/63A priority patent/GB1023655A/en
Priority to FR935212A priority patent/FR1356812A/fr
Application granted granted Critical
Publication of US3321660A publication Critical patent/US3321660A/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
    • H01J43/24—Dynodes having potential gradient along their surfaces

Definitions

  • the photomultiplier tube generally comprises a photocathode and one or more secondary electron emissive electrodes, or dynodes, positioned to receive electrons that are either emitted from the photocathode or from another dynode.
  • the dynodes are normally of particular configuration so that the electrons will pass from one multiplying stage to another, and electron multiplication will occur at each stage as the electrons pass through the various stages of the tube.
  • These photomultiplier tubes also include a collector electrode, or anode, from which output signals are taken. Due to the stringent requirements for particular configurations of the various electrodes, particularly the secondary electron emissive dynodes, these tubes are rather complicated to construct and thus are expensive to produce.
  • an elongated, tubular insulating member having on the inner surface thereof a secondary electron emissive means.
  • a thin electrically conductive means Positioned within the tubular member is a thin electrically conductive means which extends substantially along the axis of the tubular member and is spaced from the secondary electron emissive means.
  • the secondary electron emissive means is prepared so as to have a relatively high surface resistance.
  • FIG. 1 is a longitudinal sectional view of a photomultiplier tube made in accordance with this invention
  • FIG. 2 is a longitudinal sectional view of another embodiment of this invention.
  • FIGS. 3 through 7 are partial longitudinal sectional views of secondary emissive structures made in accordance with this invention.
  • FIG. 1 there is shown a secondary electron emission amplification structure.
  • the structure comprises an elongated electron multiplier tube 10 which is illustrated as being sensitive to an input light and is thus a photomultiplier tube.
  • the photomultipliers structure is shown merely as an example of the use of this invention. It should be clearly understood that the secondary emission amplification structure shown can be used for amplification of electron currents generated by agencies other than visible light, e.g. ultraviolet radiation, X-rays or heat.
  • the tube 14 comprises a tubular envelope 12 which is shown as being substantially cylindrical.
  • the envelope 12 may be made of some insulating material such as glass.
  • a separate support (not illustrated) for the secondary emissive coating 14 may be used and the inner surface of the envelope 12 is shown as an example of an insulating support that is of proper configuration.
  • the secondary emissive coating 14, in this embodiment, is selected for its properties of high secondary electron emission and its photosensitivity, i.e. its sensitivity to an input light 16 incident through a window portion 17 of the envelope 10 which portion is transparent to the input light 16.
  • the secondary emissive coating 14 is prepared to have a high surface resistance, i.e. greater than 10 ohms per square. Details relating to the surface resistivity may be found in the attached appendix.
  • the secondary emissive wall coating 14 may be prepared for example by evaporating antimony and condensing a thin, e.g. 10- to 10* cm. thick film of antimony on the inner surface of the envelope wall. Subsequently, the thin film of antimony is reacted with cesium vapor. The cesium vapor may be obtained by flashing a cesium pellet (not shown) within the tube 10.
  • Methods of preparing cesiated antimony surfaces which are photosensitive and which are also secondary emissive surfaces are well known in the art. One example of such a method is described in a book by Zworykin and Ramberg, entitled Photoelectricity, published by Wiley, 1949, e. g. see p. 96.
  • an electrical conductive means which, in the embodiment shown in FIG. 1, comprises a thin, e.g. less than 5 mils, metallic wire 20.
  • the radius (r of the wire 20 is chosen small enough, in relation to the inside radius (r of the coating 14 on tube 12, so that only a small fraction of the emitted electrons from the tube wall will be intercepted by the wire 20.
  • the wire, which is supported at both ends, may be, for example, approximately 1 mil in diameter throughout most of the tube and may be made of a material such as tungsten.
  • the central wire 20 is effectively thickened, e.g. the wire 20 may be supported by a spring 22 which is an effectively thicker wire.
  • the spring 22 may function to hold the wire 20 taut and as an electron collector or output electrode.
  • a separate collector electrode 24, which comprises a hollow tubular electrode spaced around the spring 22, or directly around the central wire 20 if the spring 22 is omitted, may be used.
  • the collector electrode 24 is positioned adjacent to the high potential end of the resistive secondary emissive coating 14.
  • the spring 22, or the collector electrode 24 have a substantially larger diameter than the central wire 20.
  • the wire 20 may have an enlarged diameter, in this region, which may be used as the collector electrode.
  • r of the electrical conductor 20 Another factor which determines the gain obtainable from the tube 10 is the radius (r of the electrical conductor 20. It can be shown that the percentage of electrons which will be collected by the central conductor 20, and thus the percentage of electrons which will not be multiplied will increase as the ratio of r /r increases. Thus, assuming a /2 inch radius (r for the tube, and a /2 mil wire radius (r for potential differences between the wire and the tube wall ranging from approximately 2,000 volts adjacent to the window 17 to approximately 500 volts adjacent to the collector 24, about 2.5% to 5% of the electrons will be collected by the central wire 20. Each time the wire radius r is doubled, with the other parameters remaining constant, the number of electrons collected by the central wire is also doubled. Thus, the ratio r /r should be very small, so that most of the electrons will miss the central wire without a magnetic field.
  • the enlarged radius of the wire 20, or the spring 22, or the collector electrode 24 should be about 100 mils in the example previously considered.
  • the least permissible diameter of the collector electrode would have different values.
  • a potential is applied between the two ends of the secondary emissive (and also photoemissive) coating 14 by means of source 18.
  • the source 18 may be of the order of one thousand to several thousand volts.
  • the primary electrons eject a number of secondary electrons which number is a multiple of the number of primary photoelectrons.
  • the secondary electrons are again drawn toward the middle of the tube 10, miss, for the most part, the central wire 20 and are incident on a still more positive portion of the secondary emissive wall coating 14.
  • the now multiplied electrons again eject a number of secondary electrons equal to their own number, multiplied by the secondary emission gain of the surface.
  • the electron current is repeatedly multiplied as the swarm of electrons, originally initiated by the light 16, moves down the length of the tube 10. It should be noted that the electrons miss the central wire 20 in the absence of any applied magnetic field, i.e. one in addition to the earths magnetic field.
  • a light shield (not shown) may be placed around the tube 10 except in the area of input window 17 if desired.
  • FIG. 2 there is shown another embodiment of this invention.
  • This embodiment difiers from that shown in FIG. 1 in that coating 30 is provided adjacent to the input window 16 which is photoemissive while a secondary emissive coating 32 extends throughout the balance of the envelope.
  • the photoemissive coating may be selected for its high efficiency as a photoernitter, while the resistive secondary emissive coating 32 may be selected for its property of high secondary emission.
  • the photoemissive coating 30 may now be selected for its response to various selected wavelengths.
  • FIG. 2 also differs from that shown in FIG. 1 in that a central accelerating electrode means 34 which includes insulating fiber 36 is provided.
  • the insulating fiber 36 may be made of a material such as quartz.
  • the insulating fiber 36 is coated with a highly resistive, e.g. approximately 1000 ohms per square has been found suitable, conductive coating 38 such as tin oxide.
  • a highly resistive e.g. approximately 1000 ohms per square has been found suitable, conductive coating 38 such as tin oxide.
  • conductive coating 38 such as tin oxide.
  • the electrical connections for the tube with a resistive central wire may be as shown in FIG. 2.
  • the secondary emissive coating is in the form of a resistive spiral or helix 40.
  • the resistive spiral may be formed for example by tracing, or by evaporating through a vibrating mask (not shown), a helix of a coating having a much lower surface resistance than the inside wall of the tube 12.
  • the strip width is w:4.4r
  • the strip width becomes about 1.8 mils.
  • a one ohm resistance may be formed by a platinum film approximately 10- centimeters thick.
  • FIG. 4 there is shown anembodiment of this invention which comprises a mosaic 46 of minute conducting secondary emissive elements deposited on a resistive surface film 48.
  • a secondary emissive mosaic 46 as well as aphotoemissive mosaic, is the conventional mosaic used in aninconoscope 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.
  • FIG. 5 there is shown an embodiment of this invention which utilizes a spiral or helical resistive coating 52 having a mosaic of secondary emissive and photoemissive material 54 deposited on the turns of the spiral coating 52 and on the envelope between the turns of the coating.
  • the materials described in connection with FIG. 5 may be similar to those previously described in connection with FIGS. 3 and 4.
  • FIG. 6 there is shown an embodiment to this invention which utilizes double spirals of resistive material.
  • a spiral 58 is interleaved with a spiral 60 with both connected to appropriate potential sources.
  • alternate spaces between the spirals may be practically field free, preventing possible deterioration of the sensitive material between them resulting from ionic conduction.
  • the materials may be similar to those described in connection with PEG. 3.
  • FIG. 7 there is shown an embodiment of this invention utilizing a resistive spiral or helix 66 having a conductive coating 68 of resistive materal deposited on the turns of the helix 66 and on the envelope between the turns of the helix.
  • a resistive spiral or helix 66 having a conductive coating 68 of resistive materal deposited on the turns of the helix 66 and on the envelope between the turns of the helix.
  • On the conductive resistive material 68 there is a mosaic of photoemissive and secondary emissive material 70.
  • the resistance of the spiral 66 in this embodiment may be computed in connection with FIG. 3, While the resistivity of the coating 68 should be greater than the desired eifective surface resistivity (e.g. 1 megohm or more).
  • the photoemissive mosaic 70 may be similar to that described in connection with FIG. 5.
  • a central conductive means such as the condoctor 20 shown in FIG. 1, or a centrally positioned insulating material having a resistive coating thereon, such as shown in FIG. 2, may be used, but a showing is omitted in FIGS. 3 through 7 to simplify the drawings.
  • the electron multiplier structure has been shown as a photoemissive device since this is a particularly useful one of the many functions that can be accomplished by the use of this invention.
  • applicants novel electron multiplier structure can be used with any source of primary electrons.
  • the appendix contains the derivation of equations relevant to the design and operation of tubes made in accordance with this invention.
  • APPENDIX r is the radius of the central conductor, e.g. wire 20 in r is the radius of the inner surface of the envelope 10.
  • Az is the distance separating the points of impact of the electrons, in other words, the distance between multiplying stages.
  • f is the fraction of electrons lost by interception by the central wire.
  • e is the charge of the electron.
  • eV is the energy of electron emission.
  • V is the potential of the point of emission.
  • V is the potential of the central conductor.
  • V is the Voltage applied between the photocathode and the point on the tube wall where the last impact takes place.
  • T is the transit time from emission to impact.
  • L is distance from the photocathode to the last point of impact (this is very slightly less than the distance from the photocathode to the collector).
  • G is the gain provided by the tube.
  • R is the surface resistivity
  • X is a parameter including voltages and radii.
  • N is efiective number of stages of electron multiplication of the tube.
  • the interception of electrons by the thin central wire 20 ranges between 5 percent at the photocathode end and 2.5 percent adjacent to the collector electrode 24 in the example given, wherein the ratio of r;; to r is 800 to 1.
  • the collecting portion of the central wire 20, or the spring 22, or the collector electrode 24 should be at least 0.050 in diameter.
  • the current gain of the multiplier phototube can be determined as follows. In the design shown in FIG. 2 (and to a close approximation in the design shown in FIG. 1) the motion of the electrons is governed by the equations.
  • V V and dV/dz can be treated as constants.
  • the first relation of motion i.e. for the radial coordinate, may be employed to determine (for r /r l) the time of transit T of an electron emitted with small initial velocity from the time of emission to the time of impact of the opposite wall, leading to 1r L dV r 722 111 (Q i 1
  • R should be (7.1) 10 ohms per square at the bottom (photocathode) and (4.1) ohms per square at the top (point of final impact).
  • the impact voltage will be given by This varies from 83 to 249 volts from the bottom to the top of the tube while the distance between impacts varies from 0.373 to 1.12.
  • An electron multiplier comprising;
  • An electron multiplier comprising;
  • a photomultiplier tube comprising;
  • said coating of material being adapted to have a potential gradient established from adjacent one end thereof to adjacent the other end thereof;
  • said electrode including an effectively larger diameter part adjacent one end thereof for collecting multiplied electrons.
  • An electron multiplier comprising;
  • said secondary electron emissive means including a spiral resistive coating
  • said secondary electron emissive means being adapted to have a potential gradient established from adjacent one end thereof to adjacent the other end thereof;
  • said conductive means having a radius that is related to the inner radius of said envelope by a ratio of the order of 1 to 1000".
  • An electron multiplier comprising;
  • said electron emissive means comprising a secondary electron emissive coating and a photoelectron emissive coating
  • said electron emissive means being adapted to have a potential gradient established thereacross; and (e) conductive means extending substantially along the axis of said envelope and spaced from said electron emissive means;
  • An electron multiplier comprising;
  • said secondary electron emissive means comprising a coating of resistive material and a mosaic of secondary electron emissive particles positioned on said coating of resistive material;
  • said secondary electron emissive means being adapted to have a potential gradient established from adjacent one end thereof to adjacent the other end thereof;
  • An electron multiplier comprising;
  • said secondary electron emissive means comprising a helix of resistive material and a mosaic of secondary emissive material on the turns of said helix and on said envelope between said turns;
  • said secondary electron emissive means being adapted to have a potential gradient established from adjacent one end thereof to adjacent the other end thereof;
  • An electron multiplier comprising;
  • said secondary electron emissive means comprisa first helix and a second helix of resistive material
  • said secondary electron emissive means being adapted to have a potential gradient established from adjacent one end thereof to adjacent the other end thereof;
  • -(e) conductive means extending substantially along the axis of said envelope and spaced from said secondary electron emissive means; the inner radius of said envelope being of the order of 1000 times as large as the radius of said conductive means.
  • An electron multiplier comprising;
  • said secondary electron emissive means comprising a helix of resistive material having a coating of resistive material on the turns of said helix and on said envelope in the areas between said turns;
  • said secondary electron emissive means further comprising a mosaic of secondary emissive material on said coating of resistive material;
  • said secondary electron emissive means being adapted to have a potential gradient established from adjacent one end thereof to adjacent the other end thereof;
  • said conductive means having a radius that is of the order of one thousandth as small as the inner radius of said envelope.

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US197467A 1962-05-24 1962-05-24 Electron multiplier having resistive secondary emissive surface which is adapted to sustain a potential gradient, whereby successive multiplication is possible Expired - Lifetime US3321660A (en)

Priority Applications (5)

Application Number Priority Date Filing Date Title
BE632654D BE632654A (es) 1962-05-24
NL293150D NL293150A (es) 1962-05-24
US197467A US3321660A (en) 1962-05-24 1962-05-24 Electron multiplier having resistive secondary emissive surface which is adapted to sustain a potential gradient, whereby successive multiplication is possible
GB17010/63A GB1023655A (en) 1962-05-24 1963-04-30 Electron multiplier
FR935212A FR1356812A (fr) 1962-05-24 1963-05-17 Multiplicateur d'électrons

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US197467A US3321660A (en) 1962-05-24 1962-05-24 Electron multiplier having resistive secondary emissive surface which is adapted to sustain a potential gradient, whereby successive multiplication is possible

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BE (1) BE632654A (es)
FR (1) FR1356812A (es)
GB (1) GB1023655A (es)
NL (1) NL293150A (es)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3436590A (en) * 1966-03-02 1969-04-01 Itt Electron multiplier
US3506868A (en) * 1967-05-22 1970-04-14 Bendix Corp Positive-type electron multiplier channels connected in series
US3634690A (en) * 1970-03-23 1972-01-11 Itt Tubular photocell with secondary emission from internal surface
US3634713A (en) * 1969-09-08 1972-01-11 Bendix Corp Electron multiplier having means for altering the equipotentials of the emissive surface to direct electrons towards the anode
US3976905A (en) * 1973-07-05 1976-08-24 Ramot University For Applied Research And Industrial Development Ltd. Channel electron multipliers
US4604545A (en) * 1980-07-28 1986-08-05 Rca Corporation Photomultiplier tube having a high resistance dynode support spacer anti-hysteresis pattern

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2209847A (en) * 1936-10-24 1940-07-30 Int Standard Electric Corp Secondary emission device
US2210034A (en) * 1935-11-08 1940-08-06 Emi Ltd Electron multipler
US3233140A (en) * 1961-07-25 1966-02-01 Univ Illinois Crossed-field dynamic electron multiplier

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2210034A (en) * 1935-11-08 1940-08-06 Emi Ltd Electron multipler
US2209847A (en) * 1936-10-24 1940-07-30 Int Standard Electric Corp Secondary emission device
US3233140A (en) * 1961-07-25 1966-02-01 Univ Illinois Crossed-field dynamic electron multiplier

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3436590A (en) * 1966-03-02 1969-04-01 Itt Electron multiplier
US3506868A (en) * 1967-05-22 1970-04-14 Bendix Corp Positive-type electron multiplier channels connected in series
US3634713A (en) * 1969-09-08 1972-01-11 Bendix Corp Electron multiplier having means for altering the equipotentials of the emissive surface to direct electrons towards the anode
US3634690A (en) * 1970-03-23 1972-01-11 Itt Tubular photocell with secondary emission from internal surface
US3976905A (en) * 1973-07-05 1976-08-24 Ramot University For Applied Research And Industrial Development Ltd. Channel electron multipliers
US4604545A (en) * 1980-07-28 1986-08-05 Rca Corporation Photomultiplier tube having a high resistance dynode support spacer anti-hysteresis pattern

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NL293150A (es)
FR1356812A (fr) 1964-03-27
GB1023655A (en) 1966-03-23
BE632654A (es)

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