US3039017A - Image intensifier apparatus - Google Patents

Description

June 12, 1962 c. E. BROWN ETAL IMAGE INTENSIFIER APPARATUS Filed April 12, 1960 28 zoEomd INVENTORS CLINTON E. BROWN JACK W. CRENSHAW 3,039,017 Patented June 12, 1962 3,039,017 IMAGE INTENSH IER APPARATUS Clinton E. Brown, Artillery Road, Marlhank Farm, Yorktown, Va., and Jack W. Crenshaw, Denbigh, Va. (409 Sunset Drive, Downingtown, Pa.)

Filed Apr. 12, 1960, Ser. No. 21,843 7 Claims. (Cl. 315-41) (Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America without the payment of any royalties thereon or therefor.

This invention relates generally to radiation pickup apparatus, and more particularly to an image intensifier and reproduction device.

To increase scientific knowledge of the geography of stellar bodies beyond that obtainable by conventional telescopic photography, it has been proposed to view stellar bodies from cameras carried by space craft in flight. In order to obtain an informative picture of a stellar bodys geography, particularly the poorly illuminated portions thereof, from an orbiting space vehicle, substantial multiplication of the image formed by the camera is required. Although image amplification and reproduction devices have been heretofore devised, such for example as those utilizing electromagnetic or electrostatic image multipliers, the number of stages of these prior art multipliers necessary to reproduce a sufiiciently detailed image result in cameras too bulky for utilization in present day small sized space vehicles. Moreover, the structural arrangements of present day image multipliers have not been found to be capable of satisfactorily withstanding the high G forces developed during launching.

Accordingly, it is an object of the present invention to provide a new and improved light, or other, radiation image multiplier.

-It is also an object of this invention to provide a new and improved radiation image amplifier and display apparatus.

Another object of the instant invention is to provide a novel electron multiplier and storage device.

Still another object of the present invention is the provision of a rugged and compact cathode ray type tube capable of picking up and reproducing an image without alteration or loss of the characteristics thereof.

A further object of this invention is to provide a novel image amplifier tube having a high degree of sensitivity and utilizing a simplified and rugged construction.

Another further object of the present invention is to provide a novel radiation reproduction tube for use in fluoroscopy.

Still another further object of this invention is to provide a new and improved image intensifier and storage camera exhibiting a fast shutter time.

According to the present invention, the foregoing and other objects are attained by the provision of an evacuated envelope composed basically of a radiation sensitive layer which emits electrons in response to image radiations directed thereon, a tandem arrangement of aligned honeycombs, secondary ernissive surfaces formed on the honeycombs for intensifying the discrete electron streams travelling in the channels formed by the honeycombs, an electron sensitive target upon which the discrete electron streams are directed, and means for reading out the electron irnage developed on the target.

A more complete appreciation of the invention and many of the attendant advantages thereof will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein:

FIG. 1 is a schematic view of one embodiment of the image camera tube of the present invention; and,

FIG. 2 is a schematic view of an alternative embodiment thereof.

Referring now to the drawing wherein like reference numerals designate identical or corresponding parts throughout the several views, and more particularly to FIG. 1, one embodiment of the image tube 11 according to the present invention is shown as consisting of an evacuated substantially cylindrical or rectangular envelope 12 having a glass or plastic faceplate 13 transparent to the radiations directed thereon, and enclosing, in the following enumerated sequence, an image surface 14, an electron multiplier assembly 15, a reproduction section 16, and a pair of conventional electron guns .17 and 18.

Image surface 14 may be a semitransparent photocathode film deposited on the inside surface of the tube faceplate 13 which film emits electrons from each illuminated elemental area thereof proportional to the intensity of the radiation striking the area. The electron multiplier assembly 15, disposed closely behind image surface 14, consists of a number of substantially identical sized honeycomb segments 19 formed of an insulating material and being disposed in axial alignment along the longitudinal axis of envelope 12. The infinitesimally small sized cells, or openings, in each honeycomb segment are formed in identical patterns thereby forming vacuum channels, ducts, or columns, for constraining the electron fiow therethrough into narrow individual streams normal to input screen 14. The cells may be of any desired crosssectional configuration, but it will 'be apparent to one skilled in the art that the smaller the cell size and the larger the density of the cells, the greater will be the resolution of the composite electron image formed by the totality of the independent electron streams generated by the honeycombs.

Interposed between the abutting faces of each of honeycomb segments 19 are transmissive type dynodes 21 formed of a thin film, on the order of 1000 angstroms, of a material having a high secondary emission coefiicient, such for example as gold coated potassium chloride. Suitable positive potentials of progressively increasing magnitudes are applied to successive dynodes from a conventional electrical energy supply 22. By reason of this honeycomb-dynode arrangement, the electrons emitted by photocathode 14 will be drawn through the cells of the first honeycomb toward the first dynode in a multiplicity of independent streams of diverse intensities. Impingement of the electrons on the forward surface of the first dynode will result in the release of a larger number of electrons from the immediate vicinity of the back surface thereof. The aforedescribed intensification operation is repeated in each successive stage of multiplier assembly 15 thereby considerably intensifying the number of electrons in each of the streams arriving at the output of the multiplier. The degree of amplification provided by any particular sized multiplier assembly may be readily increased by reducing the thickness of each honeycomb segment, increasing the number of segments and the number of dynodes interposed therebetween. Due to the collimating effect of the honeycomb channels, the number of electrons in each channel are directly proportionate to the intensity of the radiation falling upon the elementalphotocathode surface directly above each channel input. It will be appreciated by those skilled in the art that the hereinbefore described ganged multiplier provides a compact and rugged structural arrangement for obtaining extremely large image amplification with a high degree of resolution.

In the embodiment of FIG. 1, the reproduction section 16 is composed of a target electrode, or screen, 23 adjacent to, and axially aligned, with, the multiplier assembly, a guard ring 24 formed of an annular film of conductive material deposited on the inside envelope surface closely behind the target plate, and an unidirectional potential energy source 25 electrically connected to the guard ring for effecting positive polarity energization thereof. Target electrode 23 may be a conventional storage element consisting of a sheet of dielectric material 26 coated with of film of semiconductive material, such for example as germanium or the like, on the surface exposed to the electron streams from the multiplier output. The conductivity of the semiconductive material 27 determines the rate at which a charge placed on an elemental surface area thereof will spread.

Electron guns 17 and 18 are located in the neck portion 28 of evacuated envelope 12 and their electron beams impinge upon the dielectric surface 26 of target electrode 23. Electron gun 17 emits an undirected spray of high energy electrons, while electron gun 18 emits a beam of low energy electrons, said beams providing for image storage and read out operations, respectively, as will be more fully explained hereinafter. The direction of the low energy beam of electron gun 18 to affect point by point scanning of surface 26 may be accomplished by conventional electrostatic deflection plates 29 positioned between target electrode 23 and the electron guns.

impingement of the high energy electrons from gun 17 upon an elemental area of dielectric surface 26 will result in the secondary emission of electrons if the corresponding elemental area of semiconductive surface 27 is being bombarded simultaneously by electrons from multiplier assembly 15. The resultant secondary electrons are attracted to the positively electrified ring 24. Since electrons are leaving an elemental area of one side of target electrode 23 while electrons are being received simultaneously on the corresponding elemental area of the other side of target electrode 23, each elemental area, or point, on dielectric surface 26 eifectively acts as a minute condenser having a charge representative of the intensity of the electron stream impinging thereon. The operating period of electron gun 17 is made to be short compared to the time constant characteristic of semiconductor film 27 in order that it itself may effectively act as an insulating medium. When electron gun 17 is cutoff, the reproduced image formed by the charges developed on target electrode 23, may be preserved, or stored, for an indefinite time period.

To read out the stored image on target electrode 23, electron gun 18 is actuated to scan every elemental area of dielectric surface 26. The sequential impingement of the low energy electron beam upon each elemental surface area aifects the discharge of each stored elemental charge on dielectric surface 26 across an output resistance 31. In order that the semiconductor film may effectively act as a conductor medium, the scanning rate is made to be long compared to the time constant characteristic thereof. From the foregoing description, it will be apparent to one skilled in the art that the instantaneous magnitudes of the output signal developed across resistance 31 are truly representative of the radiations incident upon each elemental area of photocathode 14. Obviously, the intelligence in the output signal of image tube 11 may be made available to scientists by utilization of conventional telemetry and magnetic tape recording techniques.

If photographs of the image are desired, as illustrated in FIG. 2, an image tube 32 consisting of vacuum tight enclosure 12 for housing the image surface 14, and electron multiplier assembly 15 of FIG. 1 may be employed. In this application the reproduction section may consist of a planar target screen 33 formed of an electron sensitive phosphor which will give a visible reproduced image in response to the impingement of electrons thereon from photomultiplier 15. A conventional camera 34 may be positioned at the base of the envelope to take photographic pictures of the visible image formed on the phosphor plate.

For the purpose of realizing the advantages of high speed photography, short exposure times can be obtained by periodically interrupting the path between the accelerating potential source 22 and one or more of dynodes 21 by conventional means, such for example as a circuit switch 35. Application of periodic short pulses to the dynodes will result in the taking of still shots by the image tubes of FIGS. 1 and 2.

It is to be understood that although the device of the present invention has been described with reference to its application in space photography, it is not so limited, but by the use of a photocathode sensitive to X-ray wave lengths, it can be readily used as a sensitive fluoroscope in medical and industrial applications minimizing the presence of radiation hazards.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A radiation pickup device comprising a vacuum tight enclosure, a radiation sensitive input screen therein capable of emitting electrons correlative to the radiation projected thereon, an electron sensitive output screen therein capable of forming an image representative of the radiation projected onto said input screen, an electron multiplier assembly positioned between said input and output screens, said assembly being formed of one or more parallel spaced transmissive type dynodes formed of a film of material having a high secondary emission coefficient for intensifying the electrons impinging therein as a result of the radiation projected on said input screen, honeycomb segments formed of insulating material contiguously disposed between said dynodes for support thereof and providing aligned minute channels normal to said dynodes for collimating the electrons flowing therethrough, means for applying potentials to each of said dynodes of progressively increasing magnitudes to accelerate the flow of electrons through said multiplier assembly, and means for reading out the representative image formed on said output screen.

2. An image pickup device comprising a vacuum tight enclosure, a first screen therein responsive to the incidence of input radiation to cause emission of electrons, a second screen therein responsive to the incidence of electrons for forming an image representative of the input radiation incident upon said first screen, an electron multiplier assembly comprising one or more tandem arranged honeycomb s-egments formed of insulating material providing a plurality of axially aligned minute channels for effecting a collimated electron flow through said assembly, one or more transmissive type dynodes formed of a film of material having a high secondary emission coefficient supported by said segments for intensifying the electron flow in said channels, said dynodes being substantially parallel to said screens and perpendicular to said ducts, means for applying potentials to each of said dynodes of progressively increasing magnitudes to accelerate the flow of electrons through said multiplier assembly, and means for reading out the representative image formed on said second screen.

3. A radiation reproduction device comprising a vacuum tight enclosure, a planar screen therein responsive to the incidence of input radiation to cause emission of electrons, an electron multiplier assembly therein formed of a plurality of aligned honeycomb segments formed of insulating material having identical patterns of openings therethrough thereby providing a plurality of axially aligned minute channels for collimating the electron flow through said multiplier assembly in response to electron emission from said planar screen, one or more parallel spaced transmissive type dynodes formed of a film of material having a high secondary emission coefiicient supported by said segments for intensifying the electron flow in said channels, means for applying potentials to each of said dynodes of progressively increasing magnitudes to accelerate the flow of electrons through said multiplier assembly, a target electrode therein comprised of a relatively thin layer of semiconductive material facing said planar screen and a relatively thin layer of insulating material, an annular electrode therein proximate to said target electrode, means therein for bombarding said target electrode with a beam of high energy electrons, an output circuit electrically connected to said target electrode through said enclosure, and means for scanning said target electrode with a beam of low energy electrons in a point by point manner.

4. A device according to claim 3, and including means for periodically interrupting the application of potential energy to at least one of said dynodes.

5. A radiation reproduction device comprising a vacuum tight enclosure, a planar input screen therein responsive to the incidence of input radiation to cause emission of electrons, an electron multiplier assembly therein formed of a plurality of aligned honeycomb segments forming minute ducts normal to said planar screen, a plurality of transmissive types dynodes spatially supported by said honeycomb segments normal to said ducts,

6 means for applying potential energy to said dynodes, said dynodes being formed of a film of material having a high secondary emission coefiicient perpendicular to said ducts, and a planar target screen therein formed of an electron sensitive material for producing a visual image representative of the input radiation incident upon said input screen.

6. A radiation reproduction device according to claim 5, and including a camera positioned proximate to said enclosure for taking a photograph of said visual image produced on said target screen.

7. A radiation reproduction device according to claim 5, and including means for periodically interrupting the application of potential energy to at least one of said dynodes.

References Cited in the file of this patent UNITED STATES PATENTS 2,254,617 McGee Sept. 2, 1941 2,464,420 Snyder Mar. 15, 1949 2,667,599 Rajchman Jan. 26, 1954 2,805,360 McNaney Sept. 3, 1957 2,817,781 Sheldon Dec. 24, 1957 2,821,637 Roberts Jan. 28, 1958 2,836,755 Sommer May 27, 1958 2,841,728 McGee July 1, 1958 2,942,133 McGee June 21, 1960

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