US3603828A

US3603828A - X-ray image intensifier tube with secondary emission multiplier tunnels constructed to confine the x-rays to individual tunnels

Info

Publication number: US3603828A
Application number: US794507*A
Authority: US
Inventors: Edward Emanuel Sheldon
Original assignee: Sheldon Edward E
Current assignee: UNITED JEWISH APPEAL OF GREATER NEW YORK
Priority date: 1969-01-28
Filing date: 1969-01-28
Publication date: 1971-09-07
Anticipated expiration: 1988-09-07

Abstract

This invention relates to image intensifiers of multiplier type and which are especially useful for X-ray images. The novel device is characterized by construction in which each of the discrete X-ray beams corresponding to individual image points strikes the multiplying channel and is prevented from impinging in addition on adjacent multiplying channels. It is found that in order to accomplish this objective the lateral deviation of said multiplying channels between their entrance apertures and their exit apertures cannot exceed l mm.; and in addition that the difference of the level of said entrance apertures and said exit apertures cannot exceed 1 mm.

Description

tlnited Mates Patent [72] Inventor Edward lEmnnuel Sheldon 30 lists! 30th Street, New Yorlt, NY. 10016 [211 App]. No. 796,507 [22] Filed Jan. 20, 1969 [2 3] Continuation-impart of Ser. No. 519,814,

Nov. 26, 1965, Pat. No. 3,461,332

[45] Patented Sept. 7, 1971 [54] l t-111111 lit RAGE ilN'lllENSll llElR TlUfiE WllTlll SECONDARY EMHSSIIUN MULTHPLHEIR TUNNlElLS CONSTRUCTEID T0 CONIFME THE Ell-RAYS T0 lllDlli/IIDUAL TUNNIElLS 10 Claims, 414 Drawing Figs.

[52] 1.1.8.0 313/65, 313/82, 313/105, 250/213 [51] lint. Cl ..ll101j 29/68, 1101 13/23, HOlj 31/26, HOIj 31/50 [50} Field ofSenrclh 3l3/94,92, 106, 104, 105, 65, 94; 250/213, 63

[56] References Cited UNlTED STATES PATENTS 2,879,406 3/1959 Wachtel 250/213 2,996,634 8/1961 Woodcock 313/92 3,237,039 2/1966 Fyler 313/92 3,461,332 8/1969 Sheldon 313/65 Primary Examiner-Roy Lake Assistant Examiner-V. Lafranchi Attorney-Polachek & Saulsbury ABSTRACT: This invention relates to image intensifiers of multiplier type and which are especially useful for X-rays images. The novel device is characterized by construction in which each of the discrete X-rays beams corresponding to individual image points strikes the multiplying channel and is prevented from impinging in addition on adjacent multiplying channels. It is found that in order to accomplish this objective the lateral deviation of said multiplying channels between their entrance apertures and their exit apertures cannot exceed 1 mm.; and in addition that the difference of the level of said entrance apertures and said exit apertures cannot exceed 1 mm.

PATENTEU SEP 71971 3,603,828

SHEET 1 [M II-RAY IMAGE IN'IFNSII IEII 'I UIIIIE WI'I'III filECONDAIRII lEl /IISSIGN MULTIIPLIIEII TIUNNEIJF ICGNSTIIIJCTIED T CONFINIE TII-IIE II-IIAIIS T0 INDIVIDUAL TUNNIELS This invention relates to the image converters and image intensifiers for various radiations and especially for the use with X-rays or neutrons and to be used independently or in combination with television camera tubes, and represents a continuation in-part of my copending U.S. Pat. application Ser. No. 519,814, filed Nov. 26, 1965, now U.S. Pat. No. 3,461,332 issued Aug. 12, 1969, and which is a continuationin-part ofU.S. Pat. No. 3,400,291 filed Aug. 28, 1964. In addition the instant application has common subject matter with my U.S. Pat. No. 3,279,460 filed Dec. 4, 1961 and issued Oct. 18, 1966; with U.S. Pat. No. 3,149,258 filed Sept. 9, 1954 and issued Sept. 15, 1964; with U.S. Pat. No. 3,021,834 filed Nov. 28, 1956 and issued Feb. 30, 1962; and with U.S. Pat. No. 2,877,368 filed Mar. 11, l954issued Mar. 10, 1959.

My invention will be useful in all situations which require the conversion of radiation from one wavelength to another wavelength of spectrum.

My invention will be useful also for intensification of the brightness of the images to be reproduced.

In addition, my invention is of great importance for improvement of resolution of images reproduced.

In addition, my invention will make it possible to miniaturize the present image converters, and image intensifiers, such as are described in my U.S. Pats. Nos. 2,555,423 and 2,555,424; and which are used in the field of diagnostic radiology.

My invention will be better understood when taken in combination with the accompanying drawings.

IN THE DRAWINGS FIG. I shows the novel image intensifier.

FIG. Ia shows novel electron guide.

FIGS. Ib, 11c, Id, lie, and llfshows modifications of the electron guide.

FIGS. 2, 2a, 3, 4 and 5 show modifications of the image intensifier.

FIGS. 7 and b show cascade image intensifiers.

FIGS. 6 and do show the use of two tubes in cooperative relationship.

FIGS. 9, III and Mia show a novel composite screen.

FIGS. Ill and 112 show image intensifier provided with a fiber-optic lens.

FIG. 13 shows a novel television camera tube.

FIGS. 113a, 113b, III: shows novel acoustic image converters.

FIG. I4 shows a novel electron gun.

FIG. 115 shows a novel storage tube.

FIG. 115a shows a novel curved electron guide and multiplier.

FIG. 15b shows a modification of the novel curved electron guide and multiplier.

FIG. 1150 shows a novel spiral electron guide multiplier.

FIG. 115d shows image intensifier tube.

FIG. I6 shows a novel X-ray image intensifier.

FIG. 117 shows a neutron image intensifier.

FIG. 1171; shows a modification of neutron image intensifier.

FIG. 118 shows a novel infrared image intensifier.

FIG. 118a shows a modification of infrared image intensifier.

FIG. 19 shows an image-intensifying tube with angulated type of electron multiplier.

FIG. I90 shows modification of the angulated electron multi lier.

FIG. IIIIb shows a vacuum tube with a curved-type electron multiplier.

FIG. 20 shows a novel television pickup tube with electron multiplier.

FIG. 211 shows a vacuum tube with a novel electron multiplier of fiber-optic type.

FIG. 211a shows a modification of the device shown in FIG. 211.

FIG. 22 shows a novel image tube with a perforated imagereproducing screen and using reflected electron beam.

FIG. 22a shows a modification of the device illustrated in FIG. 22.

FIG. I shows a novel vacuum tube which comprises a photoemissive photocathode 2 such as of Cs, Na, K with Sb, Bi or As or of a mixture of aforesaid elements, such as KCsSb or NaKSb. For infrared radiation CsOAg or CsNaKSb will be more suitable. The photocathode 2 may be deposited on the end wall of the tube 1 or on a transparent supporting plate such as of quartz, glass or mica 3 or of arsenic trisulfide. The visible or invisible radiation image of the examined object 4 is projected by the optical system 4a on the photocathode 2 and is converted into a beam of photoelectrons, having the pattern of said image. The photoelectron beam has to be focused in order to get a good reproduction of the image. In the devices of the prior art, he focusing was accomplished by electrostatic or electromagnetic lenses which are large and heavy. As a result, the standard image tubes are bulky and cannot be miniaturized. In my device, I eliminated the electrostatic or electromagnetic lenses which made it possible to make a miniature device. The problem of focusing the electron beam without the use of electron-optical devices, was solved by the use of a novel mechanical device such as the apertured guide 5. The guide 5 comprises a plurality of tunnels 6, each tunnel is of microscopical diameter and extends through the whole length of the guide. Each of the tunnels must be insulated well from the adjacent ones. It was found that there are various ways to construct such guide. In one preferred embodiment the guide 5A may be constructed of a plurality of hollow tubes 15 of glass or of plastic, having their both ends open and being of 10 microns diameter or less, and held together by silicone or other temperature-stable plastics. or by fusing them together by heating, see FIG. lla. For a good resolution of the image, I use ISO-250,000 of such tubes stacked together in one-square-inch area. In some cases each of tubes I5 is coated on inside walls with a conducting layer, such as of aluminum, 7a or semiconducting layer 7c, which is connected to an out side source of electrical potential.

The tubes 15 may be also held in position at their ends only either by fusing them at the ends only, by heat, or by gluing them together with silicone or other plastic material compatible with vacuum, or mechanically, for example, by threading their ends only into a mesh screen mounted rigidly in the tube.

In cases in which resolution of images is not important, the guide 5 may be constructed of a number of apertured glass plates combined in one unit as was described above for tubes 15. In the preferred embodiment of invention the tubes 15 of glass or plastic may be coated on their outside walls with a conducting material 701 or semiconducting material 7c and next with the insulating material such as of fluorides, glass, plastic, MgO, or silicon oxide 50, extending along the entire length of said tubes and around their entire circumference. Next the inner glass or plastic wall of the tubes 15 is leached out to make the conducting 7a or semiconducting or resistive layer 7c face the lumen of the tunnels I5. In this construction the insulating coating 50 is of material resistant to the leaching agent and it will serve as a support for other layers. The material for uniting the tubes should be resistant to temperature necessary for vacuum processing. Plastic material such as fluorocarbons, polyethylenes such as fluoroethylenes or silicon compounds such as silicates are useful.

If the tubes I5 are united by heating them, the outer walls of the tubes may be clad before the fusion with a glass or other material which is resistant to the leaching agent and which melts easier than the layer 50. In some cases the dielectric layer 50 may serve for this purpose as well.

In some cases, the first coating to be applied to the walls of the tubes 115 may be of a secondary electron emissive material 2%, as shown in FIG. Id, which may be of semiconducting type such as CsSb, of insulating type such as of fluorides, MgO, or allcali halides such as KCI or of aluminum oxide, or of conducting type such as He, Ni, Cu, or of a mixture thereof. In some cases layer Sill and 7a or 70 should be able to tolerate temperature of 600 C. The dielectric layer 50 as was explained above serves as a support for all other layers and extends along the entire length of the tunnels.

The secondary electron emissive layer 20 should preferably extend along the entire length of the tubes and cover the inside lumen of tunnels 6 on all sides.

In some cases the coating 20 may be also applied to the inside walls of the tubes 15, after they have been coated with the conducting and insulating layers and after they were leached as was described above, but the results are inferior than in the method described above.

It is also possible to coat the inside walls of the tubes 15 with a conducting layer and with a secondary electron emissive layer 20 by evaporation or electrolytically. In such case the tubes 15 do not require any leaching at all. The results however are inferior to the method described above because the secondary electron emissive coating is not uniform. In my preferred construction the deposition of the secondary electron emissive material is done on the external surface of the walls of said tubes which makes it practical to produce a homogenous and uniform deposition of the secondary electron emissive material. As was explained above the subsequent leaching of the glass makes the secondary electron emissive material face the lumen of the tunnels 612.

Another preferable method of building the guide 5 is to use a fiber plate which consists of plurality of fibers of 5 to microns diameter made of glass or plastics.

The fibers are coated with a dielectric material 50 such as a suitable glass, plastic, fluorides, silicon oxide or other silicon compounds, as shown in FIG. 1f. In some cases the fibers and their coating should be able to tolerate temperature of 600 C.

The material for uniting the fibers should be resistant to leaching agent used for the glass and also resistant to temperature necessary for vacuum processing. Among plastic materials fluorocarbons, polyethylenes such as fluoroethylenes or silicon compounds are the best. All these fibers are glued together chemically or are fused together by heating, Such a fiber plate is now subjected to a leaching process in which the glass or plastic fibers are etched out and dissolved by a suitable chemical. The leaching agent does not attack however, the coating of fibers. We will obtain therefore, after the leaching is completed, a guide 5F having as many tunnels 6 as there were original fibers in the plate. The fiber plates can be constructed of fibers having only 6 microns in diameter. Therefore the tunnels 6 will have a diameter of approximately 6 microns. If it is important to have the tunnels of a uniform diameter, the fiber plate should be made of fibers which have a coating of glass or plastic which does not deform during the heating fusion. In some cases it is preferable to have an electrically conducting coating on the inside walls of tunnels 6. In such case, a layer of Al, Pd, Au or Ag may be deposited on the inside walls of the tunnels 6 either by evaporation or electrolytically. A preferred method of providing a conducting 7a or semiconducting or resistive 7c coating inside of tunnels 6 is to use the fiber plate in which the fibers before combining them in one unit are clad with a metallic coating or in which the dielectric coating such as of glass or plastic comprises a metal. In such case an additional insulating layer 50 which may be of a glass, plastic, fluorides or silicon oxide or silicates should be deposited outside of the metallic layer to provide a good electrical insulation of tunnels 6 from each other. It should be understood that tunnels 6 and all their modifications have the length a few times, which means at least 2 times, larger than the diameter of their apertures 42.

Also fiber-optic mosaics may be used for construction of the electron guide 5. Such mosaic can be made of a plurality of fibers, having a core of one kind of glass and a coating of another type of glass. All these fibers are fused together by heating. Such a fiber-optic plate is now subjected to a leaching process in which the core of the fibers is etched out and dissolved by a suitable chemical. The leaching agent does not attack however, the coating of fibers. We will obtain therefore, after the leaching is completed, a plate having as many tunnels as there were original fibers in the fiber-optic mosaic. It should be understood that these glass fibers and fibers described above may be also provided with a coating of secondary electron-emissive material 20 and of the conducting material 7a before being coated with another type of glass. Therefore after the core of said fibers is leached out the secondary electronemissive layer will face the lumen of tunnels 6.

I found that the tunnels made of the metal tubes in the prior art could not give a good resolution of the images because the metal tubes could not be made of diameter smaller than 0.50 mm. and could not be reproduced uniformly. In my device glass or plastic tubes are used which can be produced of diameter of0.01 mm. and which can be produced with a great degree of uniformity in great numbers. My device will need 200,000 tubes or more.

It should be understood that the work glass in the specification and in the claims embraces all kind of glasses and synthetic plastic materials as well.

Another electron guide is shown in FIG. 10. The vacuum tube 1A has a source of electrons such as photocathode 2 or an electron gun 40 and a novel electron guide 5C.

The guide 5C comprises in vacuum tube 1A a plurality of perforated members 60 such as plates or meshes of dielectric material, such as glass or plastic and a plurality of electrically conducting perforated members 61 such as plates or meshes of steel, nickel or copper. The dielectric members 60 and conducting plates or meshes 61 are stacked together and glued together or fused in an alternating pattern. In this way plural tunnels 6a are produced which have walls of alternating strips of dielectric material and of a conducting material. All electrically conducting members 61 may be connected to an outside source of potential.

An improved method of producing apertures plates or meshes is to use a fine-focused electron beam for perforating continuous sheets of suitable materials. This method is used for electrically conducting materials such as nickel, copper beryllium and for dielectric materials such as plastics, fluorides or glass as well.

In some cases it is advantageous to intensify electron beam by a secondary electron multiplication. This is accomplished in my invention by coating the perforated apertured conducting members 61 of the guide 5D in vacuum tube 18' with a secondary electron emissive material 20a such as calcium fluoride, alkali halides, such as KC], aluminum oxide, CsSb, and Ni or Be, of the thickness of 50 to 250 angstroms as shown in FIG. 1b. This coating 2011 may be deposited by evaporation or by electrolytic process, and is deposited before the

members

60 and 61 are combined together in one unit, their apertures being aligned and forming thereby elongated tunnels 60 having the length larger than diameter of said apertures. It should be understood that the various arrangements of dielectric members 60 and of conducting members 61 coated with layer 200 come withing the scope of my invention. For example, I may use a few dielectric members 60 for each conducting member. The conducting members 61 coated with the layer 20a are connected to an external source of the electrical potential. Each member 61 is provided with a potential a few kv. higher than the preceding one. In the vacuum tubes of the prior art the emitted secondary electrons had to be focused by means of bulky magnetic devices to prevent loss of resolution. In my device, all electron-optical focusing devices can be eliminated and still a better resolution is obtained than in the prior art. The secondary electrons must travel through the tunnels 6a and are restrained to the size of such tunnels. The tunnels 6a or 6 should preferably be in some cases at an angle to the photocathode 2. In some cases the apertures 42 of tunnels 6 or 6a should have a bevelled shape.

It was found however that the perforated plates of meshes whether of conducting type or of dielectric type cannot give as good resolution, as the electron guides made out of hollow tubes or of fibers which were described above. It was also found that conducting mesh screen covered with insulation and stacked together do not make tunnels of uniform diameter and shape as it is required for the best resolution of the images as it is impossible to bring plurality of such screens into a perfect registry with each other as it was successfully done in electron guides using hollow tubes or leached out fiber plates.

My novel imaging device may use all embodiments of the electron guides described above. The novel image tube ll shown in FIG. 1, as described above, has the photocathode 2, on the support 3, electron guide 5 and an image-reproducing screen 8. The image-reproducing screen 8 comprises luminescent or electroluminescent material such as ZnSCdS, ZnSAg or zinc silicate and is covered on one side with an electron-transparent, light-reflecting layer 9 such as aluminum. The layer 9 prevents the light emitted by the screen d to scatter back to the photocathode 2. The image of the examined area 4 is projected by the lens 4a on the photocathode 2 and is converted into a beam of photoelectrons having the pattern of said image. The photoelectron beam is accelerated by the electrical fields 39, enters the guide 5 through the apertures t2 and is focused by said guide onto luminescent screen 8. It leaves the guide through the apertures 42a, is accelerated again by the fields 39, strikes the screen d and reproduces a visible image therein. This novel image tube does not require any electron-optical focusing devices for good resolution of the image.

I found that the closer the guide 5 is to the photocathode 2, the better is the resolution of the image. In particular, a distance of a small fraction of 1 millimeter will give the best results, the distance of a few millimeters will give a much worse resolution. The vacuum tube 1 shown in FIG. 1 must be provided with a unidirectional electrical potential for acceleration of photoelectrons from the photocathode to the guide 5, and from the guide 5 to the image-reproducing screen 8. The accelerating potential may be applied to the conducting cylinders which transmit electrons or coating 39 on the inside of the tube envelope or to the conducting layer 7 such as of aluminum. The higher the accelerating potential is, the brighter the reproduced image will be in the screen 8. There is, however a limit to the strength of the accelerating potential which is set by the dielectric strength of the tube. The use of guide 5 allows the potential to be spread between the photocathode 2 and screen 8 over a longer distance and without loss of resolution. Therefore it will be possible now to use, in the tube 1, a much higher potential than it would be feasible without said guide 5. The conducting layer 7 maybe 50-400 A. thin so it will be completely transparent to the photoelectrons emitted by the photocathode 2. The conducting layer 7 or semiconducting layer 70 is connected to an outside source of potential and may be preferably in contact with the conducting or semiconducting coating on inner walls of tunnels 6. The layer 7 may be continuous. ln some cases, a perforated metallic layer 7b will be better. The perforations in the layer 7 corresponding to the apertures 42 of the tunnels 6, may be made by blowing a strong current of air through the tunnels 6. Another method of producing the apertured conducting member is to use a perforated plate or mesh screen of conducting material such as 43 describedbelow.

The length of the tunnels 6 in the guide 5 must be longer than the diameter of the apertures 42 of said tunnels. The actual length will vary according to the application of my guide and the type of vacuum tube. However the tunnels of the guide should be at least a few times longer than the diameter of the apertures. The longer is the guide 5, the greater difference of potential can be applied to both sides of said guide. The greater is the the difference, the more acceleration of the electrons can be achieved. This brings about a greater image intensification, which was one of the purposes of my invention. The acceleration potentials may be supplied from an external source of potential connected to the layer '7 or 413 or to separate grids which transmit electrons and are disposed on both sides of the guide 5, or to conductive rings 39 mounted on the walls of the vacuum tube. In the devices of the prior art, it was impossible to provide a large potential difference, because the separation of the fluorescent screen a from the photoelectric screen 2 could not be longer than 0.25-0.5 cm.; exceeding this distance caused a prohibitive loss of resolution of the image. In my device, in spite of the elimination of the focusing electron-optical lenses or fields, l can provide separation of the photocathode 2 and of the fluorescent screen 8 of any desired length without a loss of resolution of the image. I found that for the best resolution in this embodiment ofinvention the walls of the tunnels 6 facing the lumen of said tunnels should be free from a photoelectric material or from a secon dary electron-emissive material.

The electron beam from the photocathode 2 carrying the image is therefore guided by the electron guide 5 to the imagereproducing screen ill. It is accelerated to impinge on said screen 8 with a sufficient velocity to produce therein a visible image of increased brightness.

The tunnels 6 may be uniform in their diameter through the whole length of the guide 5. The tunnels 6 may have also a divergent form, in which the exit apertures are larger than the entrance apertures. In such case the electron beam will be enlarged upon its exit from the guide. The tunnels 6 may be also of a convergent form in which the exit apertures are smaller than the entrance. In this case the electron beam will be demagnified on its exit from he guide.

The separation of guide 5 from the photocathode 2 will cause some photoelectrons to strike the solid parts of guide 5, instead of entering the apertures 42 in the guide. In this way, a space charge may be produced on solid parts of guide 5,which may interfere with the photoelectron image. I found that development of the space charge is the cause of failure of such devices. The conducting layer 7 will prevent this from happening as the charges will be able to leak away through layer 7. In some cases, it is preferably to mount guide 5 in contact with the photocathode 2 or the photocathode may be deposited directly on the end face of guide 5 instead of on the end wall of the tube or on a supporting member 3, as is shown in FIG. 2. In this construction the conducting layer should be a perforated layer 7b or a perforated member 43. The discontinuous electrically conducting layer 7b may be also made by evaporation and will have -90 percent transmission for electrons. In some cases it is preferably to use an electrically conducting member 43 in the form of a metallic wide-mesh screen or perforated plate of metallic material or of a perforated member coated with an electrically conducting; material such as tin ox ide. The member 43 is mounted on the end face of the guide 5 in such a manner that openings of the screen or plate 43 coincide with one or with a few apertures 42 of the guide 5. The screen or mesh 13 is connected to an outside source of electrical potential in the same manner as layer 7b. In this construction I found that a problem arises because of the chemical interaction between the photoemmissive material of photocathode 2 and the materials of guide 5. It is important therefore to select materials which do not poison the photocathode. Lanthanum glass is chemically compatible. Still a protecting separating layer 20 of a light transparent material such as of calcium fluoride, MgO, or of silicon monoxide may be needed. The layer 2a should be preferably perforated and have a transmission for photoelectrons of 80-90 percent. The apertures of the layer 20 must coincide with the apertures 42 of the guide. The layer 2a may be prepared by deposition on the top of the layer 43 of a continuous layer first and next by rupturing said layer with a strong current of air blown through tunnels 6, so that only the parts overlaying the solid portions of the guide 5 will remain in position.

Also, the phosphor screen b may be deposited directly on the end face of guide 5. This construction facilitates markedly the construction of tube 11, as guide 5 with the imagereproducing screen 8, and in some cases also with the photocathode 2 may be prepared outside of vacuum tube 11, and then introduced into tube in in. one unit, and mounted therein.

In some cases, either only the photocathode 2 or only the image screen d are in contact with the guide 5. In case the screen 8 is separated from the guide 5, the separation, for the best results, should be preferably a fraction of l millimeter.

In some cases it is preferable to prevent the electrons which travel through the tunnels 6 or 6a in the guide from striking the walls of said tunnels. This can be accomplished by providing the walls of said tunnels which face the lumen with a conducting or semiconducting coating 7c as shown in FIG. 2a. The conducting coating may be of aluminum or chromium. The semiconducting coating may be of tin oxide or of titanium oxide. The coating 7a may be connected to the perforated conducting member 43 or to layer 7 which again may be connected to an outside source of electrical potential. As all tunnels 6 are in contact with the layer 7 or with member 43, walls of said tunnels will have a potential which will repel electrons travelling through said tunnels.

In some cases, the second

perforated member

43 or 7 mounted on the opposite end of the guide 5, may be discontinuous from the coating 7a by terminating said coating 7a before reaching one end face of the guide 5. In this construction, the second member 43 may be connected to the external source of electrical potential to provide acceleration for electrons.

In the embodiment of invention, shown in FIG. 1 and 2, and 2a, the tunnels 6 of the guide 5 run normally to the photocathode 2 and are straight from the beginning to their end to prevent photoelectrons from striking from the beginning to their end to prevent photoelectrons from striking the inside walls of the tunnels.

It will bee understood that my device may use a plurality of electron gui'des 5. In such case electron-accelerating means such as grids, rings, cylinders of meshes connected to a suitable source of potential may be interposed between the electron guides.

The semiconducting coating or resistive 7c in some cases is preferably to conducting coating because it allows to establish potential gradient along the length of the tunnels 6. This potential gradient will cause acceleration of electrons into direction of the exit apertures 4311 if it is connected to a suitable source of electrical potential.

In many cases it advantageous to intensify electron beam by a secondary electron multiplication e.g. by coating the inner walls of the tunnels 6a with a secondary electron emissive material such as CsSb, Ni, Be, calcium fluoride, alkali halides such as KCl or aluminum oxide or others. This coating 20 may be deposited by evaporation into tunnels 6, but the deposition is not uniform for the best results. In a preferable modification of this invention the secondary electron emissive coating 20 for the inner walls of the tunnels 6 may be provided by the methods which were described above. The glass or plastic fibers 38 before being fused or glued into a fiber plate are coated with a secondary electron emissive material 20, such as was described above. On the top of said coating 20 an electrically conducting coating 35 is applied, such as of chromium, aluminum or nickel. On he top of the conducting coating 35, a dielectric coating 36 such as of glass, plastic or of fluorides is applied, which will serve to fuse all fibers into one fiber plate as shown in FIG. 1e. It should be understood that the

coatings

20, 35 and 36 must be of material resistant to the action of the chemicals used for etching out the fibers. After the fiber plate is prepared, and the fibers are leached out, we obtain the tunnels which have the following layers. The layer facing the lumen of said tunnels is the secondary electronemissive layer 20, the next layer is the electrically conducting layer 35, the next layer is the insulating layer 36. The conducting layer 35 may be connected to the source of suitable potential for the best secondary electron emission.

In some cases, instead of conducting layer on the inside walls of the tunnels 6 it is better to have a layer of semiconducting material 70 such as of tin oxide, titanium oxide, or zinc fluoride. It should be understood that the use of semiconducting coating instead of a conducting coating applies to all modifications. In some cases an electrically resistive evaporated layer 7c may be used instead of a semiconducting layer 70. The resistive layer in a modification of my invention, instead of being a base for the electron-emissive layer 20, may replace it and serve to provide electron multiplication. In this construction the tunnels 6 should be at an angle to the photocathode or the photocathode at an angle to the tunnels.

The operation of the modification of my invention using secondary electron emissive layer 20 is shown in FIG. 4. The photoelectrons entering the apertures 42 are directed in to said apertures at an angle so that they will impinge on the walls of said tunnels 6 coated with layer 20.'In this construction apertures 42 are slanted at an angle of 45-55 and tunnels 6b in the guide 5 are straight or at an angle in relation to the photocathode 2. In some cases in order to provide the obliquity for the entering photoelectrons, instead of the tunnels, the photocathode 2 may be mounted at the angle. In such a case the tunnels will be normal in relation to the end wall of the tube. The angle at which photoelectrons enter will depend on the size of apertures and their spacing from the photocathode. The photoelectrons must have only a few-hundred-volt velocity to produce secondary electron emission greater than unity from the layer 20. The low accelerating voltage in front of the photocathode 2 creates the problem of resolution. As was explained above, my device is characterized by the absence of electron-optical focusing means. The photoelectrons leaving the photocathodes have a range of velocities 0.5 volts -l0 volts according to the wavelength of radiation used. The use of 300- to 1,000-volt accelerating potential requires a much closer spacing of the photocathode 2 to the end face of the guide 5 than devices in which the accelerating potential is a few thousand volts. It was also found that the use of the low accelerating voltage required that the conducting layer 7 be of perforated type such as layer 7b or a perforated member 43 because electrons of a low velocity will not be able to penetrate continuous layer 7.

The inside walls of the tunnels 6 should have a progressively higher potential along their length in order to cause repeated impingement of secondary electrons on the layer 20 while they are traveling to the exit apertures. It was found that the best way to provide progressively higher potential for the walls of the tunnels 6 is to divide the electron guide 5 into plural segments and to interpose between said segments apertured electrically conducting members 43 or apertured layer 7b or conducting rings which can be connected to various electrical potentials required. The conducting layer 7a or semiconducting layer 70 which are on each tunnel are connected to said apertured electrically conducting members. This construction affords a simple and practical solution of supplying progressively higher potential to all tunnels 6 in spite of the fact that we may use 200,000 tunnels or more in one electron guide 5.

I also found that devices of the prior art failed because of impossibility of obtaining an exact registry of the apertures of the end face of one electron guide 5 or one segment of the electron guide with the apertures of the next electron guide, when many guides are mounted in the tube separately and spaced apart. I found that the best way registry was obtained when the electron guide 5 described above was cut into plural segments to produce plural guides and the conducting apertures member 43 was inserted between the segments of said guide in a proper spacing from them and then all parts were fixed into one rigid unit, either mechanically or chemically or by heating. In some cases the conducting apertures members are mounted only one end faces of the segments of the electron guide and are not between them in a spaced position.

The registry of apertures of successive guides I found to be the main problem for good definition of images. The best method to accomplish a good registry is as follows. An electron guide of one of types described above is mounted on a support which has a few compartments which can be moved apart in one plane only. The electron guide 5 is cut to provide two or more smaller electron guides. The movable parts of the support are moved apart to separate these segments of the electron guide. This provides the space for the mounting of the electronically conducting member 43 such as was described above. At the same t ir ne it prevents displacement of the segments of the electron guide in relation to each other in any other plane. The electrically conducting members t3 are mounted either on the end face of the segments of the electron guide, or are mounted between the end faces of said segments. Next the movable parts of the support are moved back. This brings the segments of the electron guide into a close spacing to each other. In some cases an insulating spacer in the form of mica ring may be interposed between two end faces of the adjacent segments of the electron guide. This will be useful when the apertured conducting

members

43 or 7b are mounted between the end faces of the segments of the electron guides. Next the segments of the electron guide with the electrically conducting members 43 are fixed into one rigid unit. In this way a perfect registry of apertures of plurality of electron guides is obtained, which could not be accomplished in the prior art. The above-described units comprising plurality of electron guides can be mounted in the vacuum tube without any damage to the registry of the apertures.

The plural segments can be united either by chemical means such as by a plastic compatible with vacuum tube processing such as silicones, or fluorocarbons or polyethylenes. The segments can be also joined in one unit with mechanical means, or by the embedding material or by heating and fusing them.

It was found that a part of the photoelectrons does not enter into apertures 42 but strikes instead the solid parts of the guide 5. As the photoelectrons have velocity at which secondary electron emission is higher than unity a positive charge will develop around the apertures 42. I found that this charge reduces considerably the sensitivity of my device. This charge may be removed by mounting on the end face of the guide 5 a perforated electrically conducting member 43 in such a manner that its apertures overlie the apertures 42 of he guide. Also perforated layer 7b may be used for this purpose. The member l3 of layer 7b are connected to a suitable source of potential and will be able therefore to remove the space charge. It was found that a continuous electrically conducting layer 7 could not be used in this device because the velocity of electron was not sufficient to penetrate through it. The electrons make the exit through the apertures at the end of the electron guide 5. They are accelerated to a high velocity and strike the image-reproducing screen 8 through the layer 9. It should be understood that the multiplied electron beam after its exit from the guide 5 may be also used in combination with other devices such as targets of television tubes, storage tubes, and other vacuum tubes.

My construction will therefore produce a device which in spite of its small size is capable of a high image resolution. In addition my device will be very rugged mechanically. In addition my device will reduce the field emission in the vacuum tubes arising from the spreading of caesium vapors.

In another modification of my invention using secondary electron emission for intensification of the images the secondary electron emission for intensification of the images the secondary electron emissive layer 20a is used on the end face of the guide 5 as it is shown in FIG. 5. It is preferable to deposit first layer 20a whether it be in the form of a continuous layer or in the fonn of a discontinuous layer and then to mount on it electrically conducting member 7 or M which transmitting to electrons as shown in FIG. 5. In some cases the sequence of the layers 20a and of the member d3 may be reversed and the member 43 is the first one to be mounted on the end face of the guide. The secondary electron-emissive layer 20a in this embodiment of invention may be deposited as a continuous layer or as a discontinuous layer which covers essentially only the apertures 4l2 and the edges around them. It should be understood that in cases in which the fragility of this device is not critical the layer 200 and the member d3 supporting it may be mounted spaced apart from the end face of the guide 5E. They must be however very closely spaced in relation to said end face so that the secondary electrons will enter the apertures 42 without causing loss of resolution. The spacing smaller than 0.1 cm. will be necessary for a good resolution.

The secondary electron-emissive members 2.0a are as thin as 50-250 angstroms so that they will emit secondary electrons in forward direction when impinged by primary electrons of sufficient velocity which may be a few kv. The secondary electron-emissive member 200 may be of a conducting material such as copper, beryllium or nickel and they may be connected directly to the source of potential. The same is true about members 2011 of semiconducting materials such as caesium-antimony. If however the secondary electron-emissive material is of dielectric type such as fluorides of calcium or magnesium aluminum oxide, or alkali halides, such as KCl, a conducting layer continuous or apertured should be provided as the base for said electron-emissive member 20a. It was found that the use of dielectric type of secondary electron-emissive member gives superior results to the devices which use a conducting type of secondary electron emitter.

It was found that the device described above serious difficulties arise because of the development of space charges. The velocity of photoelectrons for the best operation of the layer 20a should be a few kv. The photoelectrons of this energy striking the solid parts or the electron guide 5 will cause secondary electron emission smaller than unity. As a result a negative charge will develop and the solid parts of the guide 5 around the apertures 42 and will cause various complications in the operation of the device. It was found that this negative charge may be removed by using a continuous type of electrically conducting layer 7 which is connected to a suitable source of potential, in preference to the use of the perforated layer 7b or of the member 43.

The guide SE in this embodiment of invention has tunnels 6 normal to the photocathode 2, the tunnels 6 have no coating 20 of secondary electromemissive material or of a photoelectron material, as it was described above and shown in FIG. 1.

It should be understood that the guide 5E may comprise a plurality of short guides, combined in one unit by mechanical means, chemical means, or by heating. Each of short guides is provided with the conducting

layers

7, 7b or 43, and has the secondary electron-emissive layer 20a on one or both end faces.

It should be understood that the guide 5 may be sliced into many separate segments, and the secondary electron-emissive screens described above may be interposed between the segments of the guide. Next all these parts may be combined in one unit, either mechanically or chemically or by heating. In this way cascade intensification of the electron beam by electron multiplication is obtained without any loss of resolution in spite of the absence of electron-optical focusing devices.

It should be understood that the segments of the electron guide 5 provided on end faces with the layer 20a should be spaced apart to provide sufficient separation for the use of a high accelerating voltage applied in this device. This spacing should preferably not exceed 0.5 cm. to preserve a good definition.

The rest of the operation of the vacuum tube 1B is the same as of the vacuum tube 1. The great advantage of this novel construction resides in ruggedness of this device.

It should be understood that the novel electron guide 5E may be used also in various vacuum tubes such as television camera tubes, storage tubes, kinescopes etc.

In the devices of the prior art the mesh screens coated with secondary electron-emissive layer were necessarily very fragile, because of their thinness. in my device the layer 20a and member 4l3 or '7 are being deposited on the end face of the guide have mechanical strength which allows the use in all operating conditions. Another novelty of my device resides in elimination of electron-optical focusing devices and without loss or resolution.

in some cases the end walls of

vacuum tube

1 or 1A or llB should be made of fiber-optic plates 12 and ll2a as shown in FIG. 3. It should be understood that this construction applies to all vacuum tubes described in this disclosure. The fiberoptic plates comprise a plurality of light-conducting fibers. Each of said fibers consists of a core of material having a high index of refraction such as suitable glass e.g. flint glass, or

quartz or arsenic trisulfide or plastics such as acrylic plastics such as lucite or polystyrenes.

The light-conducting fibers should be polished on their external surface very exactly. Each of them must also be coated with a very thin light-opaque layer to prevent spreading of light from one fiber to another. I found that without said lightimpervious coating, he image will be destroyed by leakage of light from one fiber to another. The light-opaque layer should have a lower index of refraction than the light-conducting fiber itself. Such a coating may have a thickness of only a few microns. The light-opaque coating maybe of materials such as a suitable glass or plastic. In some cases it is preferable to use glass or ceramics which will tolerate a high temperature such as of at least 600 C.

Especially glass or plastic of a lower index of refraction than the fibers and containing aluminum or chromium diffused into them are suitable materials for the coating.

In another modification the light-opaque layer such as of chromium or aluminum is deposited on the outside of the coating which in such a case may be of transparent glass or plastic.

All said fibers are glued together with silicones or are fused together by heating them to form a vacuum-tight unit. In the use of such fiber-optic plates, care must be exercised to prevent the chemical interaction between the photocathode 2 and the fiber-

optic end wall

12 or 120.

I discovered that the contact of the

end face

12 or 120 with the photocathode 2 of alkali-antimony type caused an unexpected deterioration of said photocathode. I believe that this effect is due to the presence of boric oxide or lead oxide which are common ingredients in glasses which have a high refraction index. It was found that the best way to prevent this poisoning of the photoemissive photocathode was to provide a thin light-transparent member 13 between the end wall of the tube and the photoemissive layer as shown in FIG. 3. The light-transparent separating layer 13 may be of A1 fluorides, MgO or silicon oxide and it may be of the thickness of a few millimicrons. It is important that layer 13 of A1 0 or other layer used should be of continuous, nonporous type to prevent exchange of ions through said layer. Also same results may be obtained by suing a conducting light-transparent layer such as or iridium, palladium, or tungsten of similar thickness. In some cases for the best results we may use a combination of a dielectric layer 13 such as of M 0 layer with a light-transparent conducting layer.

I also found that the

end face

12 or 120 must be very smooth to prevent nonuniformity of the photoemissive layer or of photoconductive layer which are deposited thereon. Otherwise false potential gradients will be produced which will effect the definition of the image.

Another important feature of the construction of my device is the provision for protecting the vacuum of the tubes 1A or 1C.

It was also found that the caesium of the photocathode 2 causes discoloration of the fiber-optic plates 12 or 12a, especially if they contain lead. The protecting layer 13 will prevent this complication.

The fibers of the fiber plates 12 or 12a when subject to the ionizing radiations, were found to discolor which caused losses of transmitted light. The addition of cerium to the glass used for making fibers prevented this complication.

As the fibers have a high index of refraction and alkali-antimony photocathode has a still higher index of refraction it is advisable to interpose between the end face 12 or 12a and the photocathode 2 a light-transparent layer of the thickness of the order of odd number of quarters of wavelength of the light conducted by such fibers and having an index of refraction n= wanljsth n ra cn.c be sa d n; stile index of refraction of alkali-antimony photocathode. This layer 13a may also serve as a protecting layer 13 if it is nonporous.

Another embodiment of the divide for intensification of images, is shown in FIG. 6. Two or

more vacuum tubes

1, 1A

or 1B and 1C provided with fiber-optic end walls are brought into apposition to each other and are cemented together. The luminescent image from the screen 8 is transferred by the fiber-optic end wall 12A and 12 to the photocathode 2 of the next tube without a marked loss of resolution.

A modification of this construction is shown in FIG. 6a. Two vacuum tubes IA are connected by means of a bundle of fibers 18 attached to the end walls 12A and 12. The bundle of coated fibers which were described above serves to conduct images by internal reflection of light. The bundle 1 8 may be flexible or may be rigid. The bundle 18 may be attached to the end walls 12 and 12A by an mechanical means or may be separated from the end walls of the tube. In the latter case, an optical system must be interposed between the end faces of he bundle and the end walls of the tube.

Another embodiment of my invention is shown in FIG. 7. The tube 21 is provided with composite screens or intensifying snadwiches" 22, which comprise the following layers; a lightreflecting reflecting electron-transparent layer 23, such as of aluminum or titanium, a luminescent layer 24 such as of zinc cadmium sulfide or zinc silver sulfide, a light-transparent separating layer 25 which may e of mica, glass, a suitable plastic such as silicone, or polyester, alone or in combination with a layer of aluminum oxide, silicon monoxide or other silicon compounds and of the photoemissive layer 26 which may be of any materials described above for the photoemissive layer 2. These composite screens are described in detail in my U.S. Pats. Nos. 2,555,423, 2,593,925 and 2,690,516. The intensifying screens are deposited on the end faces of the guide 5. They may be also mounted in apposition to the end face of the guide 5 and will then form a separate unit. In such a case, they will be supported by the light-transparent separating layer, which in this modification will be of glass or mica or of a mesh screen covered with a plastic and A1,O or SiO. It should be understood that the intensifying screen 22 may be also mounted in separation form the end faces of the guide 5. In such a case, the distance of separation will be governed by the same rules as described above.

In case the screen 22 is deposited on the end face of the guide, the separating light-transparent layer 25 may be preferably of silicone or polyester in combination with a thin layer of aluminum oxide, magnesium oxide or silicon monoxide or other silicon compounds.

The contact of the photoemissive later 26 with the end face of the guide 5 may cause chemical poisoning of the layer 26 and discoloration of the glass. In such case the perforated layer of materials described above for the protecting layer 13 must be interposed between the layer 26 and the end face of the guide 5. The perforated protecting layer 13 must be mounted in such a manner that its apertures will coincide with the apertures 42.

The photoelectrons from the photocathode 2 impinging on the composite screen 22 will give 10-20 more of new photoelectrons according to the accelerating voltage used.

It should be understood that a few guides 5 provided with the intensifying screens 22 may be mounted in the same tube for a cascade intensification of images. It should be understood that the rest of the operation of the vacuum tube 21 is the same as was described above.

A modification of the invention is shown in FIG. 8. In this construction, the composite screen 22 is disposed between two guides 5. The composite screen 22 may be separated from the end face of the guide 5 in which case, the light-transparent separation layer 25 of glass or mica or of a mesh screen covered by a plastic and A1,0, or SiO will serve as a support. The composite screen 22 may be brought in contact with the end faces of one or both guides S. The composite screen 22 may be deposited on the end face of guides 5 as one unit. It is an important feature of my invention that some layers of the composite screen 22, may be deposited on the end face of one guide 5 and other layers of screen 22, may be deposited on the end face of the next guide, and then both guides may be brought into apposition together. A good combination is to deposit the

layers

23, 2d and 25 on one guide and the layer as on the end face of the other guide 5. Many variations of such splitting of the composite screen 22, are feasible and it should be understood that all of them come into the scope of my invention.

It should be also understood that secondary electron-emissive layers 200 can be used in combination with the composite screens 22 as shown in FIG. a.

It should be also understood that composite screens 22 may be used on both sides of each guide 5, either in apposition or in deposition or in separation from said guide as it was described above.

If the screen 22 is brought into apposition with the guide 5 or if the photoemissivelayer 26 is in contact with the end face of the guide 5 it is important to prevent chemical interaction between the photoemissive material and the materials present in the end face of the guide 5. This con be accomplished by the depositing on the solid parts 44 of the end face of the guide a very thin protecting layer of a plastic, such as silicone or a polyester, or of a glass such as lime glass or borosilicate glass or aluminum oxide or silicon oxide, or a fluoride or a com bination of a few of these materials in the form of superimposed layers of aforesaid materials. These protecting layers ll3b should be preferably apertured and deposited so as not to obstruct the apertures 4l2 of the guide. The conducting

perforated member

7a or 43 may be deposited on either side of the protecting layers and will be connected to an external source of electrical potential.

It should be understood that the guide 5 may be sliced into many separate segments, and the screens 22 may be interposed between the segments of the guide. Next all these parts may be combined in one unit, either mechanically or chemically or by heating. This construction will provide cascade intensification of the images. The protection of the photoemissive layer 26 from interaction with the materials of the end face of the guide 5 will be the same ab was described above.

It should be understood the composite screens 22 may be used in combination with all types of the electron guide described in this specification and may serve in all types of vacuum tubes.

In case the intensifying screen 22 is not supported by the guide 5, the construction described above, may be preferably modified in the way shown in FIG. 9 and FIG. 10. The supporting layer 25 in this construction is replaced by a short bundle of light-conducting fibers 27 which were described above. Each fiber comprises a core of transparent glass or plastic 27a of a material, having a high index of refraction than said core 27b of a'material having a lower index of refraction than said core 271: seen as of a glass or plastic and of a metal such as aluminum. The coating 27b is light-opaque to prevent the escape of light and loss of contrast as was explained above. Sometimes an additional layer 270 of a light-opaque metal such as of aluminum is deposited on layer 27b or a metal such as Al or Cr is diffused into the coating 27b. All fibers are fused together at their end only or along their entire length by heating them or by gluing them into one unit. The other layers of the composite screen such as

layers

23, 24 and 26 are mounted on the respective end faces of the fiber bundle 27. This construction offers a much greater ruggedness than the previously described screens 22 and without loss of resolution.

The photoemissive layer 26 has to be protected from the interaction with the materials in the bundle of fibers 27 in the same way as was explained above, by layer 13.

Another way to make the composite screen 22 rugged without sacrificing resolution or contrast of images is shown in FIG. a. In this construction, the supporting layer of the screen 22, is replaced by a wide-mesh screen 2% which is coated on each side or on one side only with a layer of silicone 28a or of polyester or of other light-transparent heat-resistant, low-vapor plastic. On one side, of the layer 28a, there is deposited in addition, a light-transparent, very thin layer of aluminum oxide, magnesium oxide or silicon oxide or other silicon compounds. It should be understood that the construclid tion of the composite screen 22 described in FIG. ill) or Illa applies to all embodiments of my invention in which such a screen is used.

Another great advantage of my invention resides in the pos sibility of preparing the luminescent screen fl and the photoemissive layer 2 in a close spacing to each other, without the danger of contamination of the luminescent material of the screen b3 by caesium or other vapors which has not been possible in the prior art. In my device, the photoemissive layer 2 and screen ii are separated by the guide 5 which prevents the spreading of Cs to the screen b. If a perforated type of layer 7 is used, the apertures of channels 6 may be closed by a layer of nitrocellulose or of other material which will be removed by the baking processing of the vacuum tube.

When a plurality of guides 5 with intensifying

screens

22 or 7a-20a are used, it may be advantageous to process the guide 5 with the screens attached to it outside of the vacuum tube in a demountable extension of said tube. After completion the guide 5 with the screens 22 is introduced into the final vacuum tube and is mounted there by mechanical means.

The sensitivity of my imaging devices described above may be further increased by using a novel optical objective for focusing the image on the photocathode 2 which is a combination of a lens 311 with a tapered light conducting fiber bundle 32, instead of using the lens alone, as shown in FIG. 111. The fiber bundle 32 may be attached to the fiber-optic end wall 12 of the vacuum tubes carrying the photocathode 2, which were described above, by any mechanical means. The fiber bundle 32 comprises a plurality of tapered fibers 27d for the demagnifying of the image produced by the lens.

Each fiber comprises a core of transparent glass or plastic 27a of a material, having a high index of refraction and a coating 27b and of a lower index of refraction than said core 27a of materials such as of a glass or plastic and of a metal such as aluminum. In some cases it is preferable to use glass or ceramics which will tolerate a high temperature such as at least 6000 C. In some cases the coating 27b is preferably light opaque to prevent the escape of light and loss of contrast, or an additional layer 27c of a light-opaque metal such as of aluminum is deposited on the layer 27b or a metal such as AC or Cr is diffused into the coating 27b to :render it light opaque as was described above. All fibers are fixed together at their ends only or along their entire length by heating them or by gluing them chemically into one unit. If the fiber bundle should be flexible, then only the ends of the bundle should be fixed together. If a rigid bundle is wanted, then the fibers are fixed together along their entire length.

In modification of this invention, the fiber bundle 32 may enter the vacuum tube 1F and form a part of its end wall which in this case, does not have to be made of fiber-optic plate, but may be of the usual glass or metal, construction. The fiber bundle 32 will therefore form a part of the end wall of the tube or it may replace the whole end wall. The photocathode 2 is then deposited on the end face of the bundle 32. At it was described above, precautions must be taken to prevent chemical interaction between the fibers of the bundle and the photoemissive layer 2. A very thin light-transparent separating layer 13 should therefore be interposed between the end face of the bundle 32 and the photoemissive layer 2. The layer 13 may be of aluminum oxide, magnesium oxide or other silicon compounds.

Another modification of my invention which is shown in FIG. 23 will be of a great importance for television pickup tubes which have'an image section such as image orthicon or image vidicon. My device will permit elimination or electrostatic or electromagnetic focusing devices in the image section used in the present television tubes. In this construction, the photoelectrons from the photocathode 2 of the image orthicon, or other television pickup tube, are guided to the target 36) by the guide 5. The electrons transmitted through the guide reach the target 3% which is closely spaced to said guide without loss of resolution.

It was also found that the perforated mesh screen used to collect secondary electrons degrades resolution in television camera tubes. In my invention it may be replaced by a continuous conducting layer 7 which is mounted on or adjacent to the end face of the guide close to the target 30 instead of a mesh screen. The electrons from the photocathode 2 focused by the guide 5 have velocity high enough to pass though the layer 7 which is made very thin to be transparent to electrons, and to impinge on target 30. The secondary electrons from the target 30 are collected by the layer 7.

My invention can be also used for images of invisible radiations such as X-rays infrared, or images of atomic particles such as neutrons or electrons or for images formed by supersonic waves. In such case, the photocathode 2 must be modified, to make it responsive to the radiation used for image-forming purposes. The photocathode for X-rays or atomic images were described in my US. Pats. Nos. 2,555,423 and 2,690,5l6. The photocathodes described in the above patents, may be modified by using a fiber-optic bundle 27 instead of a light-transparent separating layer, as it is shown in FIG. 9, or by a screen shown in FIG. a.

The photocathode for supersonic images will comprise a piezoelectric plate 35 covered by a continuous or mosaic layer 34 of a photoemissive material such as was described above for the layer 2, as shown in FIG. 130. The layer 34 is irradiated uniformly by a source of light 65 causing emission of a beam of photoelectrons. The supersonic image is converted by piezoelectric layer 35 into a pattern of potentials corresponding to said image. This voltaic or charge pattern modulates the emission of photoelectrons from the layer 34 or of secondary electrons from the layer 36. The photoelectron beam has therefore the pattern of the original supersonic image. The photoelectron beam enters the guide 5 and remains focused by said guide. It may be also intensified if the guide has secondary electron-emissive layer a or 20 or screen 22, as was described above. The intensified electron beam may be converted into a visible image as was explained above illustrated in FIG. 1 or it may be converted into video signals as it was illustrated in FIG. 13.

In other modification 68 shown in FIG. 130 the piezoelectric plate 35 is covered by a layer of a secondary electronemissive material 36 of one of materials described above for the

layer

20 or 20a. The electron guide 5 in this modification has a hollow tunnel 37 through which the electron beam from the electron gun 40 may pass and impinge on layer 36 in a scanning pattern to produce a secondary electron emission from it. The deflecting means 53 will serve to produce a scanning motion of the electron beam. The high velocity electron beam from the electron gun 40 causes secondary electron emission from the layer 36. This electron emission is modulated by the voltaic pattern in the pate 35. The secondary electrons enter the guide 5 and are intensified there by secondaryelectron emission, as it was described above and shown in FIG. le or FIG. 4. The multiplied electrons may be converted into video signals, as it is known in the television art.

It was found that the device 67 shown in FIG. 13c failed when a standard source of light was used. It was found that

devices

67 or 69 could operate well only if the source 65 emitted only red or infrared light. In addition the source of light 65 should be preferably monochromatic or should emit in a narrow range of wavelengths. The use of standard source of light causes emission of photoelectrons ranging from 0.1- volt to 5-volts velocity. It was found that such range of photoelectrons could not be modulated with piezoelectric voltages on the plate 35.

The piezoelectric layer 35 may be of a continuous type or of a discontinuous mosaic type in all devices described.

The supersonic image devices shown in FIG. 13a, 13b, and 13c may be further improved by combining the piezoelectric layer 35 with a member 70 which intensifies supersonic waves. The member 70 may be in the form of a thin layer of a semiconducting material such as CdS or ZnO. Especially CdS of a thickness of a few microns exhibits strong amplification of supersonic waves. Addition of activators such as Cu either by diffusion of Cu into CdS or by evaporation of Cu with CdS increases this amplification effect further. The amplifying layer 70 should be plated with conducting layers 72 and 73 such as of indium or tin oxide which are connected to a source of electrical potential to provide a uniform field through said layer 70. The conducting layer 72 preferably should be light transparent. It was found that irradiation of layer 70 with light through the conducting layer 72 improves supersonic amplification. The supersonic amplifying layer 70 is responsive to longitudinal and to transverse supersonic waves and responds to a very wide range of frequencies of supersonic waves. The intensified supersonic waves emitted by layer 70 impinge on the piezoelectric layer 35 through the conducting layer 73 and produce potential or charge pattern corresponding to the original supersonic image.

In a modification of my invention the supersonic amplifying layer 70 is made preferably in the form of a mosaic 71 formed by a plurality of islands of CdS, ZnO or other suitable material and is mounted on the piezoelectric plate 35 as shown in FIG. 13a. Such a mosaic may be produced by evaporating the amplifying material through a mask or a mesh screen on a piezoelectric plate 35 which is first coated with a conducting layer 73. After evaporation of the mosaic 71, electrically conducting layer 72 is evaporated to provide the second electrode.

The piezoelectric layer 35 may be a self-supporting layer, and may serve as a support for the other layers and may also form the end wall of the vacuum tube.

It was found that difficult bonding problems arise in bonding the piezoelectric layer 35 to the glass of the envelope of the vacuum tube to make it the end wall of the tube. The use of indium seal or of epoxy seal is not efficient when piezoelectric plates of a large diameter have to be cemented, as it is required in some applications. It was found that the best solution is to use a vacuum tube envelope of a ceramic. The piezoelectric plates of a large diameter may be well joined to said ceramic envelope by brazing. In some cases the tube envelope of a metal is preferable and it was found that piezoelectric plate 35 of quartz could be well bonded with the metallic envelope. Another solution of this problem is to mount the piezoelectric layer 35 on the inside surface of the end wall of the vacuum tube.

In some cases the conducting layer 72 or 73 may be eliminated. This modification applies to all embodiments of my invention.

The piezoelectric layer 35 may be of a continuous type or of a mosaic type. It may be made of titanates, quartz, niobates or other piezoelectric materials. The layer 35 may have a high resistivity such as 10 ohm-cm., or it may be of a semiconducting material, having resistance of I0 ohmcm. to I0 ohmcm. titanates niobates can be prepared in a semiconductive form by doping them with suitable agents. The mosaic type of layer 35 may be constructed by assembling a plurality of small crystals or by evaporating a polycrystalline layer or by mechanicallygrooving a large crystal into many small units.

Supersonic waves can be conducted by the fiber bundle 27 described above. By using as a source of image-forming radiation piezoelectric or magnetostrictive generators of supersonic waves and conducting said waves to the examinedpart,

. we may produce supersonic images. Piezoelectric generators may be in the form of oscillating crystals of quartz, titanium compounds, such as titanates, Rochelle salts and other similar materials. The supersonic waves may be directed to the examined part by supersonic lenses or preferably by means of the fiber bundle 27. The supersonic waves reflected or transmitted by the examined part may be directed to the supersonic image-sensitive member by the same fiber bundle or preferably by an additional fiber bundle. The supersonic-sensitive member may have the form of piezoelectric elements, such as were described above for the supersonic generator, but smaller in size. In another embodiment of invention, the supersonic image-sensitive members is a vacuum tube provided with a piezoelectric continuous or mosaic electrode 35; said piezoelectric screen or electrode receives the supersonic image of the examined part and converts said image into an electrical pattern of potentials or charges which correspond to said supersonic image. Such a vacuum tube is provided with a source of electron beam, such as electron gun for irradiation of said piezoelectric screen or electrode. The electron beam scans said piezoelectric screen or target is modulated by the electrical pattern present on said screen or electrode and the returning modulated electron beam is converted into electrical signals in the manner well known in the television art.

In some cases the photoemissive layer 34 or secondary electron-emissive layer 36 may be mounted in a closed Spacing to the piezoelectric layer 35 as a separate unit. In such case the

layer

34 or 36 must have a perforated support such as member 43 described above. The support for the layer 36 should be preferably of conducting material but in some cases dielectric material may be also used. The unit 43-36 or the unit 43-34 may be in contact with the layer 35 or may be mounted at a very small distance from the layer 35 such as one or a few microns at most. The electrons emitted by the

layer

34 or 36 will enter the novel guide for their focusing and in some cases for their further intensification as was described above.

In another modification 69 of this invention the photoemissive layer 34 or secondary electron-emissive layer 36 are mounted on the end face of the electron guide 5. The electron guide 5 is mounted in a distance of 1 or a few microns from the target 35, as shown in FIG. 13b.

My device will be useful for construction of a novel electron gun which will offer an improvement of resolution of the electron beam. It is well known in the art that it is difficult to produce an electron bema of a small diameter without use of strong electrical or electromagnetic fields. My electron guide 5 and its modifications will permit the producing of the electron beam as small as of lO-microns diameter or less without focusing fields. This construction is shown in FIG. 14. The electron beam emerging from the source of electrons 40 enters into a closely spaced guide 5 having the apertures 42 of the size of 5 to microns, or of any other size desired and which is mounted in the vacuum tube llD.

The guide 5 has essentially the same construction as was described above and all modifications of the guide 5 apply for the use in the novel electron-gun 62 construction. In case a scanning electron beam is wanted the deflecting members 53 will direct the electron beam sequentially into various apertures 42 of the guide 5 to produce a scanning pattern. The deflecting means may also be mounted after the guide 5 instead of in front of it and will deflect the electrons after they were transmitted through the guide 5. The electrons traveling through the tunnels 6 of the guide remain focused therein. As the electron beam emerges from the apertures on the exit side of the guide 5 or 5A it has the same spot size it had at its entrance into the guide. It should be understood that the guide 5A may have tapered tunnels as it was described above, which may be of convergent form, in which case the electron beam will be demagnified upon its exit. In other cases, the tunnels may be of divergent form in which case the electron beam will be magnified upon its exit. It should be understood that apertures 42 may have a bevelled shape or other shapes.

The problem of prevention of space charge development will be solved in the same way as was described above.

In order to obtain the best definition of the electron beam the electrons which travel through the tunnels 6 of the guide 5A must be prevented from striking the walls of said tunnels. This can be accomplished by providing the walls of said tunnels which face the lumen with a conducting or semiconducting coating 7a. The conducting coating may be of aluminum or chromium. The semiconducting coating may be of tin oxide or of titanium oxide. The coating 7a may be connected to the perforated conducting

member

43 or 7b which again maybe connected to an outside source of an electrical potential. As all tunnels s are in contact with the member 43, walls of said tunnels will have an electrical potential which will repel electrons. In this modification the tunnels 6 should be normal to the electron beam and the apertures 42 symmetrical in shape.

In some cases, the second perforated member 43 is mounted on the opposite end of the guide 5 or 5A. In this construction the member 43a may be connected to the external source of potential to provide acceleration for electrons.

In addition my electron gun can bring about intensification of the electron beam produced by the electron gun 40 without increasing the noise of the electron beam, which is of the utmost importance for many devices. The intensification of the electron beam from source 40 such as standard electron or matrix gun may be accomplished by all constructions described above, for example by depositing a very thin secondary electron-emissive layer 200 on the end face of the guide 5A as was described above and illustrated in FIG. 5. The electron-emissive layer 20a is deposited on the end face of the guide. On layer 20a is mounted electrically conducting

layer

7 or 7a or 43 thin as to be transparent to electrons, and connected to a suitable source of potential. The layer 20a may be continuous, but preferably it should be discontinuous. In the discontinuous construction it may overlie the apertures 42 of tunnels d but be absent from the solid parts of the guide 5 except around the edges of apertures. In some cases the electrically conducting layer 7b which provides potential for the secondary electron emissive layer 20a is deposited not only over the apertures of the guide 5, but as a continuous layer 7 extending over the solid parts of the end face of the guide and over the apertures of the guide as well. This construction will be important for prevention of the accumulation of the space charge which may be very detrimental for the operation of the novel electron gun 62.

If the secondary electron-emissive layer 200 is used on the end face of secondary guide 5, it is preferable to deposit first said layer 20a whether it be in the form of a continuous layer or in the form of a discontinuous layer on the end face of the guide and then to mount the

member

43 or 7, as shown in FIG. 5 or FIG. 14. In some cases the sequence of the layer 200 and of the member 43 may be reversed and the member 43 is the first one to be mounted on the end face of the guide. It should be understood that in cases in which the fragility of this device is not very critical the layer 20a and the member 43 may be mounted as one unit spaced apart from the end face of the guide 5 or 5A. They must be however very closely spaced in relation to said end face so that the secondary electrons will enter the apertures 42 without causing loss of resolution.

Further intensification of the electron beam may be accomplished by using a few guides 5, 5A or 5D each of them being provided with a secondary electron-emissive

screen comprising layers

43 and 20a. All such guides are combined in one unit by mechanical means, chemical means, or by heating. In this way a cascade intensification will be obtained. It should be understood that all modifications of the guide 5 may be used for such a cascade or tandem construction.

An additional intensification of the electron beam from the electron gun may be accomplished by depositing the secondary electron-emissive layer 20 on the inside walls of the tunnels 6a, as it was explained above. The electron beam from the electron gun in such case is directed into apertures of the guide not normally but at an angle, the size of which will depend on the spacing between the electron gun 40 and the size of apertures 42. The oblique entrance of the electron beam into tunnels 6a causes impingement of the electrons on walls of the tunnels 6 and produces thereby secondary electron emission from the layer 20. The materials for the layer 20 were described above. The layer 20 is deposited on the electrically conducting layer or semiconducting layer or resistive layer 70 as it was explained above, and which is connected to the source of electrical potential. The secondary electrons emitted from the layer 20 strike the next part of the wall of the tunnels 6a. In this way, the intensification process is repeated until the electrons emerge from the tunnels 60. As the electrons emerge from the guide, the electron beam size remains limited to the size of the diameter of the aperture, but it is greatly intensified, without introduction of any additional noise.

It should be understood that my device will be useful for all sources of electron beams whether the electron beam is produced by a hot filament or by a cold emission or by a field emission. It should be understood therefore, that the definition electron gun" used in this specification and in the claims embraces all such sources of the electron beam.

It should be also understood that all modifications of the electron guide such as 5A, 5B, 5C or 5D described above may be used for the construction of the novel electron gun".

It should be understood that this novel electron gun may be used for television camera tubes, for kinescopes, for black an white images or for color images, and for storage tubes. It should also be understood that my device will be useful for devices using a broad electron beam such as applied for reading" in storage tubes or for electron mirror tubes.

My invention will be of great importance for construction of novel storage tubes such as having electron gun or a photocathode or both. The present storage tube has a very low resolution such as ,5 pair lines per millimeter. I found that this low resolution is due to inability of the storage target in these tubes to focus the broad reading electron beam into a plurality of electron microbeams small enough to depict image points of a minute size such as it is necessary e.g. for resolution of pair lines per millimeter.

This problem was solved in my device in which the broad electron beam is split into plurality of small electron beams by the novel electron guide. The split electron beam can be as small as 10 microns in diameter and will give the final image of a high resolution which was not possible before.

In conclusion my invention allows the separation of the two functions which were before provided by the storage target of the prior art, such as modulation of the broad electron beam with'a stored charge pattern and focusing of said beam.

In this embodiment of invention, shown in FIG. the electron guide 5B in the vacuum tube 1E has the electrically

con ducting member

43 or 7b of aluminum or nickel such as was described above, deposited on the end face of the guide 58. Next the secondary electron emissive layer 52 of dielectric material such as alkali halides or MgO or AL O is deposited on said conducting member 43.

The sequence of the layer 52 and of the member 43 may be reversed in some cases and the layer 52 is deposited on the end face of the guide 58 first.

The member 43 and layer 52 are deposited on the solid parts 44 of the end face of the guide 58 in such a manner as not to obstruct the apertures 42.

In operation of this storage device, the photoelectrons from the photocathode 2 or from another source of electron beam which is image modulated such as an electron gun 40 are directed to the end face of the guide 58 and impinge on the secondary electron-emissive layer 52 producing a positive or negative charge image on the end face of said guide according to the potentials used. The charge image cannot lead away because it is formed on a dielectric layer 52 as shown in FIG. 15. As a result a stored charge image remains on the end face of the guide 58 and has the pattern of the original electron image. Next a broad nonmodulated electron beam is produced either by irradiation of the photocathode 2 with a uniform source of red or infrared light, or by using an electron gun 40 for this purpose. The broad electron beam as it enters the apertures 42 of the guide 53 will be modulated by the stored charge image, and will have, therefore, imprinted on it the pattern of the original image. The broad electron beam is decelerated before the end face of the guide by a mesh screen or by conducting rings connected to a suitable source of electrical potential. The broad electron beams after being split into plurality of microbeams by the electron guide 58 is directed onto image-reproducing screen and reproduces a visible image. Instead of a luminescent screen 8 other types of screens such as scotophore screens, targets, such as dielectric tape, or photoconductive or semiconductive targets may be used as well.

It should be understood'that the storage unit 43-52 may be mounted in apposition or in a close spacing to the end face of the guide 58 as a separate unit.

It should be understood that the electron guide 58 used in this embodiment of the invention may be made by any method and may be of any type described in this specification. It should be understood therefore that reading electron beam may be intensified by secondary electron multiplication and by cascade use of plurality of electron guides.

In some cases, instead of a storage material 52 0f a dielectric type, a semiconducting material or even a conducting material such as Be, Cu, or Ni may be used. Such conducting storage layer must be deposited as a discontinuous mosaic on the dielectric solid parts 44 of the end face of the guide 53 and will be able to store the charge pattern because of its dielectric base.

It should be understood that the electron storage-guide unit may be also used in any type of vacuum tubes such as camera television tubes, kinescopes etc. and my invention is not limited to the image type of tube 1E.

It should be understood that all vacuum tubes described above may be operated in a continuous manner, or is a pulsed manner. In the pulsed operation the potential for the acceleration of electrons from the photocathode 2 or electron gun 40 is suspended for a short duration. This time interval may be also used for providing a suitable positive or negative potential to the conducting or semiconducting coating on the inside walls of tunnels 6 in order to eliminate positive or negative space charge accumulations. The positive potential may be applied to the end face of the guides 5 to dissipate the negative charges present thereon, or a negative potential may be applied to dissipate positive charges present thereon. It will depend on the type of the vacuum tube and on its operational voltages whether we will have positive or negative space charge. I

It should be understood that all types of the electron guide may be used in each embodiment or modification of my invention.

It should be understood that the word glass" in claims embraces all kind of glasses and of plastic materials as well.

It should be understood that the word light" in claims embraces all visible and invisible radiations.

It should be understood that word tunnels in his specification and in the appended claims means passages which have walls completely surrounding said passages leaving only the end faces open. It is in contradistinction to channels which are not surrounded by walls on all sides.

As various possible embodiments might be made of the above invention, and as various changes might be made in the embodiment above set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

A great improvement of definition and contrast of images was realized in the embodiments of invention shown in FIG. 15c, 15a, and 15b. In this construction the tunnels 81 of electron guide and multiplier are curved. Without going into theoretical explanation it is sufficient to say that the construction of the electron guide device built of strongly curved or even spiral tunnels in contradistinction to the straight tunnels markedly improved the performance of all my devices both in definition and contrast of images and instability of operation.

It was unexpectedly found that the image will be faithfully reproduced regardless of the curvature or in tortuosity of the tunnels 81 as long as the spacial relationship of all entrance and exit apertures remains the same. It was also found that apertures of entrance into

tunnels

6, 80 or 83 and apertures for exit from said tunnels do not have to be coaxial. It means that apertures for exit of electrons maybe in a different plane than the entrance apertures and in spite of it the image will be faithfully reproduced, as long as the spatial relationship of all exit apertures is the same as the spatial relationship of all entrance apertures.

Another important finding was that the tunnels 81 between their apertures blla and Mb may be of different diameter and shape than the apertures themselves without affecting the definition of the images. It was found that the definition of images depends only on the dimensions of apertures and how closely said apertures are spaced to each other and not on the dimensions of tunnels between said apertures.

It was further found that the diameter of the tunnels may vary within certain limits along their length without affecting the resolution of images. It was also found that the tunnels may be separated along their course from each other and that the definition of images will not suffer as long as the entrance apertures and the exit apertures of tunnels M are spaced as closely to each other as it is possible.

In view of the above findings the curved construction of the electron guide MI was found to be feasible and compatible with a good definition of images. It should be understood that the curved or spiral construction of the electron guide and multiplier b applies to all modifications of my electron guide or multiplier and that it may be used in all devices described herein. The curved construction of the electron guide 80 created a new problem The electron guide 80 uses 100 to 500 tunnels in each plane, as each tunnel represents one image point. In order to bring this number of curved tubes or other hollow members which form tunnels in apposition together, each successive curved tube must be a little longer then the preceding one. As a result the 100th tube will be considerably longer than the first tube, if the apertures of all tubes in all planes of the electron multiplier 80 should be in one and the same vertical plane, as it is shown in all FIGS. I to I14. It was found however that the great differences in length of tunnels BI cannot be tolerated because they cause great differences in output signals producing thereby incorrect contrast values. The solution of this problem is to equalize the length of all tunnels as shown in FIGS. 115a and b. It should be understood that in devices in which the contrast is not important the equalization of length of tunnels may be omitted. The construction based on equalizing the length of all tunnels results in formation of end face d2 of the electron guide 80 which has slanted shape, which means that it is inclined at an angle to the long axis of vacuum the tube, as it is shown in FIG. 15a. In some cases it may be preferable to equalize the length on both entrance and exit side of the electron guide fill as it is shown in FIG. 15b. The slanted end face 82 of the electron guide was found to cause geometrical distortion of reproduced images if conventional focusing means were used. This distortion can be improved by using suitable electron-optical lenses. It was found however that a simple solution was to mount the imagereproducing screen such as a luminescent screen 8-9 or a target of the television tube also at an angle so that the end face 82 and image-reproducing screen are parallel to each other, as shown in FIG. I511.

If the image-reproducing screen is the target of a television pickup tube, the scanning electron tube when scanning such slanted targets will cause so-called trapezoidal distortion of the image. Suitable-focusing electron-optical lenses to correct such distortion are known in the art and do not have to be described in detail.

Another modification of curved electron guide and multiplier 80 is a spiral electron multiplier $3. The electron multiplier 83 is constructed of spiral tunnels @311.

The spiral construction of tunnels is shown in FIG. ll5c. It was found to be compatible with resolution of images provided the entrance aperture @Ia and exit apertures bllb are spaced in contact or in a closed apposition to each other. The spiral construction requires however a large size vacuum tube as an array of spiral tunnels 83a occupies a much larger space than array of curved-typed tunnels M. The equalization of the length of all tunnels is necessary also in this modification of the invention and was described above.

It should be understood that the spiral electron multiplier b3 may have all modifications of electron guide and multipliers described in specification and may be used in all devices described herein.

It should be understoodm image-intensifying devices described in this specification whether they are of image-tube type or television type or of storage-tube type may be modified to make them responsible to invisible radiations of electromagnetic type such as X-ray ultraviolet or infrared, or of atomic-particles type such as neutrons or protons, or of acoustic type such as supersonic radiation.

FIG. I6 shows the X-ray-sensitive image intensifier 85. Instead of a Iight-sensitive photocathode 2 I am using a composite photocathode in a form of a screen which comprises a fluorescent or luminescent layer 2d and a photoemissive layer 26. Such screens were described above. Tor higher energy X- rays such as gamma rays a photocathode of gold or lead may be used alone or in combination and in apposition with the composite screen 22 described above. In some applications the fluorescent layer may be mounted on the outside surface of the end wall of the vacuum tube, the photoemissive layer 26 being mounted inside of the vacuum tube. The X-ray imageintensifier converts the X-ray image into a fluorescent image. The fluorescent image is next converted into a photoelectron beam corresponding to said image. The photoelectron beam is fed into the electron multiplier 5 or modifications, or 33. The multiplied electron beam exiting from the multiplier 80 is projected or focused on the image-reproducing screen such as luminescent screen e.g. Ii-b or on a target of a television pickup tube such as 30 or on a storage unit such as 4l0-52. It was found that the electron multiplier M) or $3 is very useful for intensification of X-ray images. It was found that besides the intensification of the photoelectron beam emitted from the composite photocathode 22, it provides also a direct utilization of the X-ray beam which carries the X-ray image. In particular it was found that only 15 percent of the X-ray beam is absorbed in the composite photocathode 22. The rest of the X-ray beam passes through said photocathode and strikes the input end face of the electron guide Ml or 83. The impinge ment of the X-ray beam on the secondary eIectron-emissive coating of material on the inside surface of the lumen of the tunnels M or 83a results in conversion of X-ray photons into electrons. The emitted electrons are now multiplied in the electron guide 5, M) or 33 as we described above. In order to prevent the loss of definition we must prevent separate fine pencils of the X-ray beam which correspond to separate image points from striking a few tunnels of electron guide instead of being limited to essentially one tunnel only. In addition it was found that the electron multiplier should be spaced in the vacuum tube in a symmetrical position in relationship to the sidewalls of the tube which means that it should be at the same distance from both sidewalls.

In some cases but not for X-ray applications, it is necessary to provide electron-optical demagnifying means either of electrostatic or electromagnetic type between the composite photocathode 22 and the electron guide or multiplier 5, till or 83. This arrangement will permit the use of an electron multiplier smaller than the photocathode which is important in some applications. In addition it will provide an extra intensification of the image.

In other applications it was necessary to use electron-optical means of magnifying type in order to enlarge the image from the photocathode before projecting it on electron guide or multiplier. This arrangement will permit to preserve the definition of images which is available in the photocathode and which is too high for electron guide or multiplier to reproduce. For example the photocathode may be able to produce an image having definition of IS pair lines per millimeter. On the other hand a particular electron multiplier for example can produce images of only 5 pair lines per millimeter definition. By using electron-optical magnification by a factor of 3, the image on the end face of the electron multiplier will now have definition instead of 15 only of 5 lines per millimeter and will be therefore resolved well by the electron multiplier. After the passage through the electron multiplier the image may be again demagnified if necessary and the original definition regained.

In X-ray applications the electron-optical 82a magnifying or demagnifying means can be used only if mounted between the electron multiplier and the screen for receiving electrons exited from the electron multiplier, such as fluorescent screen 8 or a target television tube 30, which is shown in FIG. 20.

It should be understood that the use of the electron-optical 82a means demagnifying or magnifying means applies to X- ray devices and to all other embodiments of the invention.

FIG. 17 shows the neutron-sensitive image intensifier 85a, wherein a neutron reactive layer 86 preferably from the group boron, lithium, gadolinium and uranium or of paraffine is placed on the face of the image tube. The protons or electrons liberated from this layer 86 under the impact of neutron radiation will strike directly or through a thin electron-pervious chemically inactive barrier layer, a suitable fluorescent layer 24, causing it to fluoresce and activate a suitable photoemissive layer 26 through the light-transparent barrier layer 25. In other cases a neutron reactive layer of copper or other gamma emitter such as cadmium 88 will be more advantageous, because of its gamma emission and may be mounted on the outside surface of the end wall 87 of vacuum tube or may be adjacent to said end wall but spaced apart from said wall 87, as it is shown in FIG. 18a.

In some cases it may be more desirable to eliminate the fluorescent layer 24 and to cause protons and electrons from the layer 86 to act on electron-emissive layer either by apposition or by focusing them with magnetic or electrostatic fields. In some cases the electron-emissive layer may be omitted and the beam of the atomic particles from the neutron reactive layer 86 may be focused directly on the electron guide and multiplier or its modifications, 80 or 83.

The fluorescent layer 24 may be also combined with the layer 86 or 88 in one composite layer and may be in this form mounted within the tube or outside of the tube 85a.

The fluorescent layer to be used in the neutron-sensitive tube may be of a similar composition as described above in the X-ray-sensitive image tube 85, but it has also to be adapted to respond most efficiently to the radiation emitted from neutron-sensitive layer by enriching it with proper additional elements. The photoemissive layer has again to be correlated with spectral emission of fluoresceht layer. The other parts of the tube 85a are the same for neutron-sensitive image tube and for X-ray sensitive image tube 85.

FIG. 18 shows infrared-sensitive image intensifier 89. Instead of the photocathode 2 a very thin layer 90 or black gold or platinum is used. The impingement of infrared radiation through a suitable window in the end wall of the vacuum tube 89 such as of sodium chloride, quartz or arsenic sulfide produces in said layer 90 a pattern of different temperatures corresponding to the pattern of said infrared image. The adjacent photoemissive layer 26 is irradiated by light from an extraneous source 91. The emission of photoelectrons in modulated by said pattern of temperatures in said layer 90. The emitted photoelectrons are directed into entrance apertures of the electron guide 5 or its modifications, 80 or 83 for multiplication. The rest of the construction of the tube 89 is the same as in any one of modifications described herein.

FIG. 18a shows another modification of the infrared-sensitive image intensifier. In this construction the layer 90 of gold or platinum is followed by a layer of photoconductive material 92 such as PbS, PbSe, PbTe or Se.

Next follows a very thin chemically inactive barrier 93 such as of MgO, SiO or SiO, or TiO,. On layer 93 is mounted a very thin conducting layer 93a such as of tungsten, platinum or palladium which may be in the'form of a continuous layer of a mosaic layer. In some cases the photoemissive layer 26 which may be in a form of a continuous layer of a mosaic layer. In some cases the photoemissive layer 26 and conducting layer 93a may be mounted spaced apart from the photoconductive layer 92. In such case the barrier layer 93 may be omitted. The infrared beam causes changes in electrical conductivity of layer 92. The layer 92 is connected to one terminal of a source of electrical power 91a such as battery or to a source of a lowfrequency electrical current? The other terminal of the electrical source 91a is connected to the conducting apertured member 94 mounted after the photoemissive layer 26 and spaced apart from it. The screen 94 is biased in such a manner that the photoelectrons from the layer 26 cannot pass through it in the absence of the infrared image forming radiation. When he infrared image arrives, it causes a drop of resistance in the layer 92. This results in the lowering of cutoff bias voltage in the apertured screen 94. Now the photoelectrons from layer 26 can pass through said member 94 and may be fed into electron multiplier 5 or its modifications or 83. The multiplied electron image has the pattern of the original infrared image and is now projected or focused on the image-reproducing screen such as a luminescent screen 9-8 or on a target of a pickup tube such as 30 or other targets or on a storage target.

My invention will allow the construction of a novel electron or other charged-particles microscope such as proton or ion microscope or the diffraction cameras. One of most vexing problems in the present electron microscopy is the damage of the examined specimen by the exposure to the electron beam. The electron beam causes irreversible changes in the structure of organic or inorganic objects as well. As a result images are obtained and recorded which in reality do not exist at all and represent artifacts only. The only way to eliminate or to reduce such artifacts is to decrease the intensity of the examining electron beam. The reduction of the intensity of the electron beam without prolonging the exposure time is unfortunately impossible because of the limited sensitivity of photographic materials used to record the electron-microscopic image. It is therefore, the objective of this invention to eliminate the artifacts by reducing either the strength of the electron beam irradiating the examined specimen or the exposure time or both.

The prevention of feedback of ions which is one of the objectives of the curved configuration of tunnels 81 and their modifications is possible also by other configurations in which the longitudinal axis deviates from the straight line between the input apertures and exit apertures of tunnels. This embodiment is shown in FIG. 19 which illustrates electron multiplier 80B constructed of two or more electron multipliers A and B of standard type with straight tunnels. These multipliers A and B have however tunnels which run obliquely which means diagonally and have opposite direction to each other. It means that the multiplier A has tunnels running from above downward whereas the multiplier B has tunnels which run from the bottom upward. If multipliers A and B are joined together, so that the exit apertures of multiplier A correspond to the entrance apertures of multiplier B, we will obtain an angulated longitudinal axis of tunnels and an angulated path of electrons through such united multiplier 808 which was the objective of this construction. The union of multipliers A and B must provide for the electrical and mechanical continuity of the walls of tunnels belonging to multiplier A and of tunnels belonging to multiplier B.

It was found that in all configurations of the composite multiplier 808 the multiplier B should be much thinner, which means that it should have a much shorter longitudinal axis than the multiplier A. This construction will bring the point of deviation of the longitudinal axis of tunnels 81d from the straight line to be close to the exit apertures 81b and till therefore stop the back-running ions before they can produce damage. For the best results the ratio of the thickness of multiplier A to multiplier B should be not less than 4 to 1. This at rangement will cause however displacement of the relation between the input apertures 81a and exit apertures 81b. In X ray image intensifiers such displacement can be tolerated only if not exceeding 1 mm., as it was explained above. This limitation does not apply to image intensifiers other radiations than X-rays or neutrons.

Other configurations of angulated tunnels are possible. In particular it was found advantageous to use a multiplier A or B with oblique tunnels in combination with a second multiplier C which has straight tunnels such as in electron multiplier 5.

This arrangement is illustrated in FIG. 19a which shows multiplier A with oblique tunnels and multiplier C with straight tunnels united together. This construction may be reversed in that the multiplier A will have straight horizontal tunnels 6 and multiplier B will have oblique tunnels.

The requirement for electrical continuity and for mechanical continuity of walls of tunnels of the multiplier A and multiplier B must be satisfied in all modifications of this embodiment of invention.

It should be understood that the electron multiplier MB in which the path of tunnels is angulated may be used also for X- ray image intensifiers. For this application it must be constructed to satisfy the requirement that the apex of angulation of the tunnel cannot be higher or lower than 1.0 mm. from the level of the entrance aperture of this tunnel. Another basic requirement is that the exit apertures of the multiplier 80B cannot deviate which means cannot be higher or lower than the apex of angulation of the tunnels by more than 1 mm.

Another requirement which has to be satisfied in X-ray image intensifiers of this type, is that the entrance apertures 81a and exit apertures 81b which belong to the same tunnel, regardless of configuration of said tunnel such as 6, M, dlld or modifications cannot be displaced by more than 1 mm. in relation to each other. This displacement means that deviation of the exit aperture from the level of the input aperture of the same tunnel cannot exceed 1 mm. The same applies to the limits of such deviation of the entrance (input) aperture 81a in relation to the exit aperture Mb in straight tunnels 5.

In addition when using such devices for the X-ray image intensifiers the input end face and the output end face of the

electron multiplier

5 or 80 or 808 or their modifications, which means the end face provided with the entrance apertures fllla and the output end face which means the end face provided with exit apertures 81b must be substantially of the same size as the X-ray reactive means such as composite photocathode 22 or other types. Furthermore

electron multiplying device

5, 80 or 80B and their modifications must be mounted coaxially with X'ray reactive means such as the composite photocathode 22 or other types.

The reasons for such specific limitations in construction of X-ray image intersifiers are as follows.

It was found that the use of curved channel multiplier device fit) or $3 or 808 and their modifications in X-ray image intensifiers caused in come cases an unexpected loss of definition and contrast of images as compared with the use of straight tunnels of the same diameter. The reason for this complication was found to be the effect of discrete X-ray pencils of radiation corresponding to individual image points which strike not only the tubular member corresponding to one of said X-radiation pencils but also the adjacent tubular members.

It was found that in spite of the use of X-ray reactive means such as X-ray sensitive screens or photocathode mounted on the outside or in the inside of X-ray image intensifier tube, a great part of X-ray radiation is not absorbed by such means but is transmitted through them and strikes the electron multiplier device which is in the path of said transmitted Xray beam.

It was found that the part of curved channel multiplier device fill or 83 or mm and their modifications which presented the biggest deviation from the straight line or curve in longitudinal axis was impinged not only by one X-ray pencil corresponding to one image point of the examined body but also by other X-ray pencils corresponding to adjacent image points. It follows that the construction of the electron multiplier device of curved type fit) or $3 or angulated type ass must be designed to prevent such overlapping by said discrete X-ray pencils. This problem cannot be solved by limiting the diameter of the tunnels as it was practiced in using straight tubular members. The solution of this problem is to correlate the definition necessary for X-ray images with the maximum radius file of curvature of the curved members fill or deviation from the straight line of their longitudinal axis. it was found that the size of the radius fill cof the curvature of tubular members fill or deviation from the straight line must not exceed 1 In addition when using electron multiplier devices for the X- ray image intensifiers the input end face of the electron multiplier f or 80, MB or their modifications, which means the end face provided with the entrance apertures Ma, and the output end face which means the end face provided with exit apertures 8111 must be substantially of the same size as the X- ray reactive means such as the composite photocathode 22 or other types. Furthermore electron multiplying device 5, $0 or MB and their modifications must be mounted coaxially with the X-ray reactive means such as photocathode 22. It was found that if these two conditions of construction are not satisfied the image will be destroyed.

In addition in electron multipliers of the type MB which are constructed of two multipliers A and B, as described above it was found that separation of the multiplier A and B from each other will damage the definition of images because the angular spread of secondary electrons which exit from the exit aper' tures of the multiplier A is of such degree that said electrons cannot be refocused again to enter into the entrance apertures of corresponding tunnels of the multiplier B.

All image tubes may be further improved by construction shown in FIG. 211. In all image intensifiers or converters which use a semitransparent photocathode or photoemissive type like 2, 22, 26 or its modifications a. large fraction of light passes through the photocathode and is lost for imaging, in addition it also causes damaging reflections of transmitted light from walls and electrodes of the tube back to the photocathode which reduces the contrast of images and reduces the signal to noise ratio of the whole device. The solution of this problem is shown in FIG. 211 in which the light transmitted through the photocathode 2 and its modifications is utilized now efficiently by the novel electron multiplier which may have straight tunnels such as multiplier 5 or which has curved or angulated tunnels such as in multiplier or 808, which have been described above.

The novel electron multiplier 50 and its modifications described above are constructed of fiber-optic plates such as were described above for the input end wall or output end wall of intensifier tubes and were illustrated e.g. in FIG. 3 0r used within the image intensifier as illustrated in FIG. I3. The fiberoptic plate 12 or 1120 in this embodiment of invention is leached out to remove only the inside part of the core of fibers and to provide thereby tunnels 50a and walls 46. A photoemissive material such as CsOAg or CsSb or multialkali antimony type is evaporated into said tunnels 50a which may be straight or may have configuration of tunnels b and fill or bid to provide the coating 2 on their surface which has both photoemissive and secondary electron-emissive property as was described above. In this embodiment of invention shown in FIG. 2B the walls of each tunnel 5dr: are formed by glass, plastic or other material which is transparent to imaging radiation which has a high index of refraction and which represents the remaining unleached part of the original core of fibers. In addition coating means are mounted on the external surface of said walls as. Each of fibers is provided with its own coating means. Such coating means should be of material of a lower index of refraction. The thickness of coating means of a lower index of refraction should be of a few microns only as was explained above, if the walls td are thick enough to have the necessary mechanical strength. If the walls or their modifications are of the thickness of less than 5I0 microns, the thickness of the coating mans may be increased to compensate for the mechanical strength. Such coating means as was described above must also comprise lighbopaque material which preferably should be spaced apart from the interface between the core and coating means, so that said interface region remains light transparent. In another alternative the lightimpervious material may be mounted on and around the outside surface of coating means and may be in the form of an extremely thin layer of black glass or of aluminum or other metal and of the thickness of a fraction of 1 micron only and not exceeding 1 micron. It was found that a good optical insulation of each of tunnels 50a or their modifications from adjacent tunnels is a very critical requirement. Without the use of the above-described light-opaque means the image will be destroyed by the light leaking from one tunnel to adjacent tunnels. It should be understood that the use of the light-opaque material in any 'form does not eliminate another critical requirement which is the presence of the coating means of a lower index of refraction than the core as it was described above.

If the electron multiplier 50 has straight tunnels, the fibers forming the array or plate may be united together with vacuum-compatible plastic material such as silicones or other fluxes or binders such as glasses or may be united together to each other directly by their own coatings by heating them.

The use of own individual coatings for each fiber of a lower index of refraction and mounted before fusing them together to each other is a very important feature of this embodiment because it produces arrays which are capable of much higher resolution and which have a better light efficiency due to their lower "packing factor," as compared with arrays in which the fibers do not have own coatings and are united by am interposed binder or flux of a lower index of refraction instead of using individual coating means described above.

In some cases the binder or flux may be added between the individually coated fibers. It may be done to facilitate the construction of curved tunnels from the originally straight tunnels. This is accomplished by forming first an array of straight tunnels and by subjecting such array to a lateral pressure while keeping the fiber-optic array at the temperature at which the walls of tunnels,coating means and of the intervening binding material soften adequately. The use of binding material does not obviate theneed for own which means individual coating means of a lower index of refraction for each fiber and it is to be understood that the use of such owncoating means for each fiber is necessary in all embodiments of the invention.

The

photocathode

2, 22 26 or its modifications may be mounted in a spaced relation to the

electron multiplier

50 or 80 or 808 or may be mounted directly on the input end face of said multipliers. In case of electron multiplier 50 however if the photocathode is mounted in a spaced relation, such spacing is very critical and cannot exceed 0.1 mm. as otherwise too great loss of resolution of image will occur. This is different from the spacing permissible when relying only on the photoelectron beam from the photocathode e.g. in case of multipliers 80, in which case the spacing may be many times larger without a great loss of resolution. The mounting of the photocathode 2 or its modifications in contact with the input end face of the electron multiplier causes however short circuiting of the photoelectrons by the electrically conducting layer 7b on which the photocathode 2 must rest.

In applications which require ruggedness, the

photocathode

2 or 22 or its modifications, if mounted on the input end face of the electron multiplier proved to be too fragile, even after strengthening it by a superimposed light-transparent layer of silicon oxide or aluminum oxide. In such applications the photocathode 2 must be mounted on the end wall of the intensifier tube or on a separate supporting member which is transparent to image-forming radiation. As was explained above the separation of the photocathode 2 from the input end face of the electron multiplier causes loss or resolution. For the best resolution the photocathode should be in contact with the input end face of the electron multiplier. It was found however that such contiguous relationship cases unexpected loss of sensitivity. The cause of it was found in the low velocity of photoelectrons which have the energy of only I to volts and in the range micron-spectrum of 0.8 micron-1.4 micron much less than 1 volt. Such photoelectrons of low energy cannot produce secondary electrons and will be lost for the image production. It is necessary therefore to accelerate photoelectrons from the photocathode 2 before they will strike the walls of

tunnels

5, 50a 81, 81d or their modifications. The

photoelectrons in order to be able to produce secondary electrons must have energy of 40-80 volts before they strike the walls of tunnels. This acceleration is obtained by difference of electrical potential between the photocathode and the entrance apertures of the electron multiplier. The need for this electrical potential gradient controls the minimum spacing, permissible from the efficiency point of view between the photocathode and input end face of electron multiplier. On the other hand the need for good resolution controls the maximum spacing possible between the photocathode and the input end face of electron multiplier. It was found that such spacing should be not smaller than 10 microns and not larger than 25 microns for light images of infrared images as it is shown in FIG. 21a.

These conditions are especially important in case of curved tunnels 81 or angulated tunnels 81d because their slanted course intercepts entering photoelectrons close to the entrance aperture of said tunnels.

The use of photoemissive materials such as CSOAg or CsSb or multialkali photocathode such as KNaCsSb which are electrically semiconducting materials may eliminate the need for semiconducting properties of walls of

tunnels

6 or 50a or curved tunnels 81 or of angulated tunnels 81d. The walls may be now either of semiconducting or of dielectric glass which depends on the amount of electron current to be drawn from the tunnels. In case the photoemissive material is not semiconducting electrically, the walls of tunnels must be electrically semiconducting to provide potential gradient along the tunnels. Lead oxide glasses which were rendered electrically semiconducting ducting by hydrogen treatment were not suitable for the embodiment of the electron multiplier 50a because of their opaqueness, which negated the internal reflection of transmitted light. The present photoemissive photocathodes are extremely transparent'to radiations above 8,000 A. The transmitted light through the photoemissive photocathode may amount in case of CsOAg to 99 percent of the original incident light in the infrared region of spectrum. The above-described embodiment of invention is therefore of special importance for devices operating in this range of spectrum as it permits retrieval and utilization of more than 50 percent of said transmitted light and improvement of sensitivity of such devices by the factor of 10 to 100. In this embodiment of invention e.g. intensifier or 95a the walls of

tunnels

50a, 81 or 81d must be of material highly transparent to the light radiation in 0.8 to 1.4 micron range of spectrum. It was found that the special infrared transmitting glasses such as AsSe or AsSeTe or Sb S are not transparent enough in this range of spectrum. The best results in this part of spectrumwere obtained with silicate glasses with rare earth elements such as lanthanum or terbium for the walls of tunnels because of their high index of refraction. The coating materials of a lower index of refraction and suitable for this range of spectrum are borosilicate glasses or magnesium fluoride, cryolite, calcium fluoride or germanium oxide. Also light flint glasses can be used for this purpose.

The germanate glasses such as Corning 9572 or 0160 may be used either for walls or for coatings of walls which must have a higher index of refraction than said coatings. The same applies to aluminatc glasses especially to calcium aluminate glasses such as Bausch or Lomb RlR2 or l0, l1, 12 or 20.

Another expedient to provide a better retrieval of light transmitted through the photocathode is to provide an oblique configuration between the

photocathode

2, 26 or 22 and the input end face of the electron multiplier 50 or its modifications. This can be accomplished by tilting the position of the whole electron multiplier 50 in relation to the photocathode or instead by tilting the position of photocathode 2 or by producing tunnels 50a 81 or 81d which run diagonally.

The input end face of the electron multiplier 50 or its modifications and the output end face of said electron multiplier are both provided with an electrically conducting layer 7b which leaves the entrance apertures 51 and exit apertures 51a uncovered as was described above. The layer 7b on the input end face must be transparent to imaging light and may be of tin oxide or of one of metals such as tungsten or platinum of a very thin construction. The input conducting layer 712 and the output conducting layer 7b are connected to the source 84 of electrical potential which must be of unidirectional type and may be of a steady or of pulsating type. The output of the

electron multiplier

50 or or 80B may be reproduced in the

same intensifier tube

95 or 95a or its modifications as a visible image on a fluorescent screen 8 or may be converted into a charge image in a target 30 of television tube or into electrical signals or video signals by various modifications of the invention described above.

The great improvement possible by this construction is due not only to the increased sensitivity of

novel image intensifier

95 or 95a or their modifications but to their much higher signal-to-noise ratio than possible in the present devices. The transmission of imaging light through the photocathode 2 or its modifications results into the loss of image information which cannot be retrieved no matter how great is the subsequent image intensification. The novel construction regains the lost information and provides therefore a much higher signal-to-noise ratio even if a much lower degree of intensification is used.

Because of this higher signal-to-noise ratio, the intensification by the electron multiplier 50a or its modifications may be limited to the use of voltage as low as l00500 volt on the input and output end face of said electron multiplier and 1000 volt on the image-reproducing screen. As a result the

intensifier

95 or 95a will require much smaller supply of electrical energy and may be extremely small. This embodiment of invention will be especially useful for electronic binoculars or for electronic goggles which can be worn by the user. The frame of goggles will support one of such intensifiers for each eye. The electron multiplier 50 may be reduced in length to O.l-O.5 mm. because its length may be limited to the path of a few passes of light through tunnels 5011 by internal reflection. The shortened length of tunnels 50a will permit a better and more uniform deposition of coating 2 by evaporation than it was possible with much longer tunnels used in present devices. If additional intensification is desired, then another electron multiplier now of a standard type may be mounted after the multiplier 50 to receive the electron beam from the multiplier 50 and to intensify it further.

It should be understood that all

novel image intensifiers

95, 95a or their modifications may be provided with fiber-optic end walls 12 on the input side of the tube or on the output side or on both sides as was described above.

The admission of light photons transmitted through he photocathode into the walls of

tunnels

50a, 6 or M or 81d depends on the index of refraction of the walls 46 of the remaining core of fibers and on the index of refraction of the adjacent coating means. The cone of acceptance of light into walls 16 of tunnels 500 will be larger if the index of the core is as high as possible in relation to that of coating means.

The fiber-optic end wall on the input side may be also con structed to limit the angle of acceptance of incoming radiation if necessary by reducing the difference between the index of refraction of the walls 46 and coating means d7. If the difference of said both indices of refraction is selected to support the propagation of a selected mode which means of a selected group of frequency of electromagnetic waves, the end wall will act then as a filter admitting only said selected wavelengths of radiation.

All

novel image intensifiers

95 or 95a or their modifications may be used for imaging of X-rays, neutrons or other invisible radiations by using a

photocathode

2, 22, 26 and modifications or a screen sensitive to such radiations as was described above.

A serious problem in all imageintensifier tubes is the presence of noise which increases strongly at voltages above ltv. The reduction of voltage is not always possible because it causes loss of luminosity of reproduced image on the fluorescent screen. The solution of this problem is shown in embodiment of invention illustrated in FIG. 22. The novel construction shown in the image intensifier 87 may be used for all image intensifiers described herein both for visible and invisible radiations; and also for all image intensifiers provided with a fluorescent image-reproducing screen regardless whether they make the use of electron multiplier device or not.

The image intensifier 87 is provided with a lightor infrared-sensitive photocathode 2 or with X-ray-sensitive photocathode 22 or with neutron-sensitive composite photocathode such as 86-24-26. Such photocathodes may be mounted on the input end wall 130 of the intensifier tube $7 or on a separate supporting member mounted in a spaced relationship to the end wall 130. The visible or invisible image is converted by respective photocathode into a beam of electrons having the pattern of said image and is focused by electrostatic 1124 or magnetic focusing means or by proximity focusing on the input apertures of the

electron multiplier

5, 50, d0 or their modifications.

The image intensifier 87 is provided with a fluorescent screen 123 which is mounted not on the end wall 8dr: as was the fluorescent screen b but in a close but spaced relationship to said end wall Mia. The internal surface of the end wall 88a is coated with a light-transparent electrically conducting layer 88b such as of tin oxide, cadmium oxide or of a very thin metal such as tungsten or gold. The conducting layer 88b is connected to an outside source M of unidirectional electrical potential. Between the exit apertures bllb of

electron multiplier

5, 50, 80, B or their modifications and the electrically conducting layer ddb is mounted a supporting forarninous plate which comprises a two-dimensional array of holes 1121 providing passages through said plate.

The foraminous supporting member 120 may be constructed in the form of a solid plate in which an array of holes is made with a predetermined spacing between each other. In another embodiment the supporting member 120 may be constructed of a mesh screen the holes of which will correspond to the holes or apertures of the solid plate. The term plate used in description and in the appended claims is meant to embrace both the solid-plate support and the mesh-screen support.

The plate 120 should be preferably of a light-opaque material such as black glass or light-opaque plastics which are compatible with a vacuum tube such as black silicones, sulfones or fluorocarbons.

The plate 120 may be of light-transparent material if the conducting layer 122 is light opaque but it was found that it is not suitable because the conducting layer 122 being extremely thin such as 0.1 to 1 micron may develop pinholes which will permit bacltscatter of fluorescent light to the photocathode or to electron multiplier device.

The plate 120 should be preferably of dielectric material to prevent lateral leakage of electrons of the beam transmitted through holes ll2ll.

if the plate 120 is made of electrical conducting material the holes t2]! may be preferably coated with an insulting layer but they may be used without insulating layer also. On the surface of the plate ll20 which is facing the conducting layer 8% is deposited a fluorescent layer 1123 of one of electron-sensitive phosphors. The layer 123 is not a continuous layer but a mosa ic layer as it is deposited only between the holes 121 and leaves the holes unobstructed for the passage of electrons. 0n the opposite surface of plate 120 which faces the electron multiplier 5 or $0 is mounted a continuous light-impervious and electrically conducting layer ll22 which may be aluminum.

The layer 122 is connected to the source of electrical potential of DC type and is provided with positive voltage of energy necessary according to application. If the plate 120 is made of electrically conducting material the layer 1122 may be of a dielectric material but it must be always thin enough to be transmitting to electrons and in addition light impervious to prevent the bacltscatter of the fluorescent light from layer 123

Claims

1. A vacuum tube for the intensifying of X-ray images formed by a beam of X-radiation comprising a plurality of pencils of said X-radiation, each of said pencils corresponding to one image point, said tube comprising in combination X-ray-reactive means absorbing a part of said radiation and converting into a beam of electrons having the pattern of said X-radiation image, an electron multiplying device, said device receiving said beam of electrons and also the part of X-radiation transmitted through said X-ray-reactive means, said electron-multiplying device comprising a plurality of separate individual empty tunnels, said tunnels having entrance apertures for the entrance of said beam of electrons and exit apertures for the exit of electrons, said tunnels having configuration of the longitudinal axis between said entrance and said exit apertures in which lateral deviation from a straight line, is not exceeding 1 mm. and preventing each of said X-ray pencils corresponding to individual image points from impinging on more than one of said hollow tunnels during the passage through said electron-multiplying device, said vacuum tube comprising furthermore means for receiving and utilizing said beam of electrons exited from said apertures, in said device furthermore the difference of the level of said exit apertures in relation to the level of said entrance apertures not exceeding 1 mm.

2. A device as defined in claim 1, which comprises in addition means producing pulses of unidirectional electrical potential and connected to said electron-multiplying device.

3. A device as defined in claim 1, in which the end wall of said tube comprises a two-dimensional array of light-conducting members, said members having a core of material of a high index of refraction and provided with coating means of a lower index of refraction than said core and having the thickness not exceeding a few microns, said precoated members united together and conducting light by internal reflection.

4. A vacuum tube as defined in claim 1, in which said electron-multiplying device comprises plurality of individual hollow members united together, and in which said vacuum tube comprises furthermore a screen for receiving said exited electrons and an imperforate and electron-transmitting member mounted between said X-ray reactive means and said screen and spaced apart from said screen.

5. A vacuum tube as defined in claim 2, in which at least two of said electron-multiplying devices are mounted adjacent to each other.

6. A device as defined in claim 2, in which said electron-multiplying device comprises plurality of individual hollow members united together, and in which said vacuum tube comprises furthermore a screen for receiving said exited electrons and an imperforate and electron-transmitting member mounted between said X-ray-reactive means and said screen and spaced apart from said screen.

7. A device as defined in claim 3, in which at least two said electron-multiplying devices are mounted adjacent to each other.

8. A device as defined in claim 4, in which said electron-multiplying device comprises plurality of individual hollow members united together.

9. A device as defined in claim 3, in which at least two said electron-multiplying devices are mounted adjacent to each other.

10. A device as defined in claim 8, which comprises fluorescent means.