US3691424A - Target screens for cathode ray tubes utilizing index generating materials that emit x-rays - Google Patents

Abstract

Beam-index cathode ray tubes comprising target screens structured with index generating materials that emit X-rays which are detected to provide index signals indicative of the position of impact of the cathode rays on the screen. The screen is comprised of special X-ray emitting regions, including thin narrow strips in register with different color-producing phosphors. Embodiments are disclosed with and without an electron-transparent aluminum layer overlaying the phosphors and the index strips.

Description

United States Patent Goodman [54] TARGET SCREENS FOR CATHODE RAY TUBES UTILIZING INDEX GENERATING MATERIALS THAT EMIT X-RAYS [72] Inventor: David M. Goodman, 3843 Debra Court, Seaford, NY. 11783 [22] Filed: Jan. 27, 1961 [21] Appl. No.: 85,353

Related US. Application Data [62] Division of Ser. No. 800,854, March 20, 1959,

Pat. No. 3,081,414.

52 us. c1 ..31s/21c,315/1o, l78/5.4, 313/92? 51 1111. C1 ..11013 29/70 [58] Field of Search ..313/92, 92 P;'l78/5.4 AC; 315/21 c, 10

[56] References Cited UNITED STATES PATENTS 2,633,547 3/1953 Law ..313/925 51 Sept. 12,1972

2,719,241 9/1955 Coltman ..313/92.5 X

Primary Examiner-Carl D. Quarforth Assistant Examiner-J. M. Potenza 57 ABSTRACT Beam-index cathode ray tubes comprising target screens structured with index generating materials that emit X-rays which are detected to provide index signals indicative of the position of impact of the cathode rays on the screen. The screen is comprised of special X-ray emitting regions, including thin narrow strips in register with difi'erent color-producing phosphors. Embodiments are disclosed with and without an electron-transparent aluminum layer overlaying the phosphors and the index strips.

7 Claims, 6 Drawing Figures PATENTEDSEP 12 I972 3.691.424

FIG. 1

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INVENTOR.

DAVID M. GOODMAN ATTORNEYS TARGET SCREENS FOR CATHODE RAY TUBES UTILIZING INDEX GENERATING MATERIALS THAT EMIT X-RAYS This invention relates to target screens for cathode ray tubes, and the like. It is a division of my pending application Ser. No. 800,854, filed Mar. 20, 1059 now U.S. Pat. No. 3,081,414 issued Mar. 12, 1963.

The use of index signals to signify the location of impact on the target screen of a scanning electron beam is recognized as a valuable tool in the generation of cathode ray tube displays. Capacity effects, secondary emission phenomena, and electro-magnetic radiation have been utilized for producing these index signals.

The primary object of this invention is to provide new and improved means for generating index signals of the class comprised of electro-magnetic radiation.

Another object of this invention is to provide im-' proved means for producing electro-magnetic radiation utilized at the target screen of a directed ray tube for purposes of examination or display.

Briefly stated, these objectives are achieved by purposely generating X-rays when the electron beam of the cathode ray tube impinges upon indicia generating elements of the target screen. These X-rays, which thus indicate the position of the electron beam on the target screen, are then filtered so that they are separated from the remainder of the radiations which may exist. The wide range of index signals that may thus be generated, the ease with which they can be filtered, their high speed of transmission, and their rapid decay upon cessation of excitation comprise the main advantages in using X-rays for this purpose.

Further advantages and objectives will become clear from the following specification taken in conjunction with the drawing wherein:

FIG. 1 represents a cathode ray tube with a target screen, index signal generating elements, and filter elements.

FIG. 2 represents a target screen configuration that may be used in the tube ofFIG. 1.

FIG. 2a illustrates a cross sectional view of the target screen of FIG. 2.

FIG. 2b illustrates a mesh-like structure that may be used as a target screen.

FIG. 3 represents another target screen configuration that may be used in the tube of FIG. 1.

FIG. 3a illustrates a cross sectional view of the target screen of FIG. 3 with three different arrangements for generating index signals.

In FIG. 1, there is shown a cathode ray tube envelope containing an electron beam forming member 12. Target screen assembly 14 is scanned by the electron beam furnished by member 12. Two radiation detectors 18 are shown located external of the tube. They are X-ray responsive and are disposed substantially parallel to and near the plane of the target screen assembly 14. Two radiation detectors 24 are shown disposed within the neck portion 26 of the cathode ray tube. Detectors 24 may be used with detectors 18, depending upon the total number of indexing signals being generated as will become clear. The target screen assembly 14 consists of members 28, 30, and 32. Member 28 in one embodiment, is comprised of phosphors or other visible radiation emitting materials arranged in narrow strips which are positioned lengthwise in the vertical direction. The horizontal scanning of these strips takes place substantially perpendicular to the thus designated vertical direction. Member 30 is an electron-transparent light-reflecting aluminum layer. Member 32 consists of strips that provide electro-magnetic index radiation when bombarded by the scanning beam of electrons. Depending upon the materialsthat these strips are made of, the electro-magnetic index radiation may extend from waves of infrared to X-rays. When this indexing radiation is in the X- ray region, members 30 and 32 may be interchanged, as will be explained infra. In FIG. 3a a target assembly is shown which is capable of generating index signals in the Hertzian range.

FIG. 2 shows, on an enlarged scale a front view of one possible arrangement of layer 28 of target screen assembly 14. Red, green, and blue color producing phosphors are arranged in the sequence red-green, blue-green and are designated 40-41, 42-43. The dimensions of the phosphor strips that are selected for this purpose are such that when the horizontal scanning beam, which proceeds linearly from left to right across FIG. 2, is constant in intensity, a substantial white image is presented to the observer. This is achieved by having the widths of the strips in the path of scan inversely proportional to the luminous efficiencies of the color producing phosphors. Phosphors are presently available which are more efficient in the green than in the blue, which is more efficient than the red. Therefore the red strip is widest, the blue strip is narrower, and the sum of the two green strips is narrowest. The efficiencies stated are those which apply when a human being is the observer. The green strip is divided as shown since the visual acuity of the eye is greatest in the green region of the spectrum. For detectors other than the eye similar considerations prevail. Strips 36 and 38 of which layer 32 is comprised, are deposited, or placed on the aluminum layer 30, or on the phosphor layer 28. These strips provide the electromagnetic index signals. The signal from strip 36 is used to excite, via suitable circuitry, the red-green phosphor combination; the index signal from 38 is used to excite, via suitable circuitry, the blue-green phosphor combination. The indexing strip is in front of the color producing strips with which it is associated so that the scanning time required for the beam to proceed from strip 36 to strip 40 is substantially equal to the overall delay that is encountered between the generation of the index signal at 36 and the time that its effect is felt at strip 40. This time delay is shown in FIG. 2 as T,,,. An equal delay T,,, is shown to exist between the indexing strip 38 and color producing strip 42. For optimum performance the period T,,, should be reduced to a minimum. This may be accomplished by using an electro-magnetic radiation index signal and by using a minimum number of wide band circuits.

In FIG. 2a there is a cross sectional view of one configuration of the screen of FIG. 2. The color producing phosphor strips 40, 41, 42, 43 are illustrated. The layer 30 of electron-transparent aluminum is also shown. Indexing strips 36 and 38 are on the side of the screen intended to face the gun of the tube, corresponding to layer 32 of FIG. 1. Strips 36 may consist of suitably prepared Hex ZnO, or Ba SiQ, activated by lead, or by tri-clinic CaMgSiO, activated by Cerium. When bombarded by the scanningbeam the strip 36 will produce electro-magnetic radiation in the neighborhood of 3,700A. This radiation has the further characteristic of decaying very rapidly upon cessation of energization. Strip 38 may consist of a tungsten wire, or molybdenum, or other material with high atomic number that generates X-rays upon exciation by the scanning beam. X-ray production is normally encountered when the scanning beam strikes layer 30, and the phosphor strips. It is made to increase substantially when the beam strikes 38 due to the fact that the efficiency of X- ray production is proportional to the atomic number of the metal of which the target is constructed. The governing equation essentially is: efficiency 1.4 X l ZV where Z is the atomic number of the target, and V is the electron accelerating voltage. For tungsten, Z 74, and at 20KV the efficiency is approximately 0.2 percent. This X-radiation also decays very rapidly after cessation of energization; more so than the phosphors of which strip 36 may consist. Hence the screen of FIg. 2a may be used to generate two electro-magnetic index signals which are distinguishable from each other, from the visible display, and from spurious radiations.

In the event that strip 36 also is preferred to be an X- ray emitter than it is desirable to make use of the characteristic radiation of the X-ray producing strips. Molybdenum for example, operated at 20KV will yield characteristic radiation at 0.71 and 0.63A. By suitable filtering, in the detector or in the screen, it is possible to distinguish the continuous distribution of X-rays produced by the tungsten strip 36, from the characteristic radiation of molybdenum strip 38. If it is desired to use a plurality of strips that emit characteristic radiation it is necessary to make a selection governed by Moseleys law f K (Z-6) which states that the frequency of the characteristic radiation is proportional to the atomic number of the emitter. For example, copper has a K-radiation at 1.5 3A when excited by SKV electrons. At KV this radiation increases much more rapidly than the background, or continuous radiation. The method of generating these characteristic spectra, and of filtering the separate radiations, is well known to those skilled in the use of X-rays. I refer to X-Rays and Electrons by Arthur H. Compton, 1926, published by D. Van Nostrand Company, and to X-Rays in Practise by Wayne T. Sproull, published by McGraw Hill, 1946, tables III, IV, and V, for further particulars. Three points will be mentioned here for simplifying the understanding of this facet of the invention. First, the characteristic radiation shows up as a sharp peak in the plot of intensity versus wavelength for a particular target. Second, an excitation energy which exceeds a certain minimum is required to excite these peaks. Third, a material that is the same as the target material used in generating characteristic spectra does not have a strong affinity for absorbing such characteristic radiation.

In view of the importance of generating these signals alternate means are illustrated in FIG. 2b, and in FIG. 3a. In FIG. 2b a mesh-like structure is formed of horizontal members 37, and vertical members 36 and 38. The interstices of this structure are filled, stripwise, with phosphors to provide the color producing strips 40, 41, 42, and 43. Member 36 may consist of a copper wire; member 38 may consist of a molybdenum wire; many other choices exist as was just explained.

The members 37 may or may not be conductive but should be substantially different from 36 or 38 insofar as X-ray producing qualities are concerned. The conductive assembly is operated at high voltage. It is clear that as the electron beam scans from left to right indexing signals will be generated. The overall time delay in the circuitry using these signals should be adjusted to T and T which represent periods of time akin to T,, of FIG. 2.

In FIG. 3, a single indexing strip 44 is shown. The signals derived from 44 will provide gating pulses for energization of the red, blue, and green phosphors. The overall time delay, between generating the index signal at 44 and energizing the first phosphor strip, is shown to be T As was stated with respect to FIG. 2, it is desirable to reduce the overall time delay to a minimum.

In FIG. 3a a cross section of a target screen configuration is shown which will provide three different electro-magnetic index signals. Phosphor layer 28 comprises strips of color emitting phosphors; layer 30 is electron-transparent and light-reflecting; layer 32, also electron-transparent, provides continuous X-radiation, and may also provide characteristic X-radiation. A constant voltage V is maintained at the side of the target screen opposite layer 32. A suitable voltage V is maintained across layer 32. When the scanning beam of electrons traverses the layer 32, electro-magnetic index signals are generated at 44a, 44b, and 440. The voltage V may be applied by means of a transparent electrical coating. This coating may be applied to member 28 or to the faceplate of the tube to which it is to be positioned, or adhered. The voltage V may be applied via member 32.

The signal at 44a occurs in the following manner. Layer 32 is maintained at 20KV and consists of a thin layer of copper for example. When 32 is scanned by 20KV electrons a continuous spectrum, and 15 3A characteristic radiation, are emitted. Either, or both, of these signals may be detected. The region 45 is maintained at V a voltage substantially different from V,. This may be accomplished by the transparent coating or by placing a wire grid at 45. The faceplate of tube envelope 10 may also be used to provide the grid; or construction as illustrated in my U. S. Pat. Nos. 2,885,591 and 2,897,388, may be used. Voltage V, may be at ground potential, or some other value lower than V thereby to produce radiation characteristics which are determined by the deceleration of the electron beam. On the other hand, V may be at a voltage higher than V This is especially the case if it is desired to generate characteristic radiation at element 45.

The signal at 44b occurs due to the removal of a strip of layer 32. When the electron beam scans this region clearly a change in the X-radiation will be produced which is detectable.

The signal at 440 also occurs due to acceleration or deceleration of the electrons. However, the layer 32 is not altered as at 44a and 44b. This may be desirable for production purposes. When X-radiation is augmented at 47 for indexing purposes in one of the manners previously set forth, it will be found that the thin, electron transparent layer 32, which is at 44c, will not materially attenuate these X-rays.

Another mode of operation of the target screen at 44c, and at 440, consists of regulating the velocity change of the electrons, and the rate of the velocity change, to produce electro-magnetic signals in the l-lertzian and microwave range. The frequency of these signals is controlled by V V and the physical distance between them.

it is clear that the previous considerations relating to the generation and filtering of the X-ray index signals also apply when the index signal generating components are admixed with the color producing phosphors. The use of tungsten or molybdenum particles for this purpose has been described in my US. Pat. Nos. 2,885,591 and 2,897,388 mentioned above.

Thus, a plurality of electro-magnetic index signals may be generated that indicate the position of a scanning beam on a directed ray tube. Many electromagnetic radiations may be used, it being clear that each radiation may serve as a separate communication or control channel. In the case of radiation in the visible range optical techniques for filtering the radiations are well known; in the microwave, or l-lertzian, range electrical filtering techniques are also well known; in the X-ray region techniques for producing and filtering monochromatic radiation are likewise well known. In addition to the Compton and Sproul references already cited, I also refer to Applied X-Rays, by Clark, Mc- Graw Hill, 1955. The wide range of signals that may be utilized constitutes one advantage of this invention. It is also to be noted that these teachings can be applied to storage-type devices, to signal generators, to quantizers, etc. In applications utilizing the scanning of a beam relative to a target where high speeds, high definition, wide band widths, and minimum distortions are required, this invention provides its greatest advantages.

Having thus described my invention, I claim:

1. A beam-index cathode ray tube with an electron gun for providing a scannable electron beam and a target screen comprising:

a first electron-sensitive fluorescent portion constructed and arranged in a geometric configuration so as to emit radiant energy within a first range of wavelengths in response to excitation via a scanning action of the electron beam;

a second electron-sensitive portion constructed and arranged in a related geometric configuration to emit radiant energy of a second range of wavelengths in the X-ray region of the spectrum, for indicating via index signals the position of impact of the electron beam;

and a layer of an electrically conductive electronpermeable material deposited on said first and second portions, said layer being constructed so as to transmit the radiant energy in the X-ray region;

in combination with index-signal producing means responsive to the transmitted radiation in the X- ray region.

2. The combination of claim 1 wherein said indexsignal producing means comprises X-ray detection means positioned inside the tube and rearwardly of the target screen.

3. A beam-index cathode ray tube, used to reproduce images of scenes televised in color, with an electron gun for providing a scannable electron beam and a target screen comprising:

a first electron-sensitive fluorescent portion constructed and arranged so as to emit light of selected colors in response to excitation via a scanning action of the electron beam;

a second electron-sensitive portion constructed and arranged so as to emit invisible radiation in the X- ray region of the spectrum, for indicating the position of impact of the electron beam;

and a layer of an electrically conductive and electron-permeable material deposited on said first and second portions, said layer being constructed so as to transmit the invisible X-radiation;

in combination with index signal producing means positioned rearwardly of the target screen inside the tube so as to be impinged upon by said invisible X-radiation transmitted through said layer.

4. The combination of claim 3 wherein said first portion comprises a plurality of different color-producing phosphor strips configured in a repeating array,

and said second portion comprises a plurality of strips of X-ray emitting material in register with the color-producing phosphor strips.

5. In combination:

a beam-index cathode ray tube with an electron gun for providing a scannable electron beam and a target screen comprising:

a first plurality of electron-sensitive strip-like portions which emit radiant energy in response to excitation by the scannable electron beam;

and in registry therewith a second plurality of electron-sensitive strip-like portions which emit X-rays in response to bombardment by the electron beam thereby to indicate the position of impact on the target screen of the electron beam;

and index signal deriving means responsive to the intensity of said X-rays for signalling the position of the electron beam;

wherein the strip-like X-ray emitting portions are comprised of electrically conductive material mounted in juxtaposition with said first plurality of strip-like portions thereby to also provide the operating voltage for the target screen.

6. The combination of claim 5 including electrically insulating strands arranged in a mesh-like configuration with respect to the strips of electrically conductive material.

7. The combination of claim 5 wherein the first plurality of strip-like portions comprises different colorproducing phosphors configured to form a repeating array of color-producing strips.

Claims (7)

1. A beam-index cathode ray tube with an electron gun for providing a scannable electron beam and a target screen comprising: a first electron-sensitive fluorescent portion constructed and arranged in a geometric configuration so as to emit radiant energy within a first range of wavelengths in response to excitation via a scanning action of the electron beam; a second electron-sensitive portion constructed and arranged in a related geometric configuration to emit radiant energy of a second range of wavelengths in the X-ray region of the spectrum, for indicating via index signals the position of impact of the electron beam; and a layer of an electrically conductive electron-permeable material deposited on said first and second portions, said layer being constructed so as to transmit the radiant energy in the X-ray region; in combination with index-signal producing means responsive to the transmitted radiation in the X-ray region.

2. The combination of claim 1 wherein said index-signal producing means comprises X-ray detection means positioned inside the tube and rearwardly of the target screen.

3. A beam-index cathode ray tube, used to reproduce images of scenes televised in color, with an electron gun for providing a scannable electron beam and a target screen comprising: a first electron-sensitive fluorescent portion constructed and arranged so as to emit light of selected colors in response to excitation via a scanning action of the electron beam; a second electron-sensitive portion constructed and arranged so as to emit invisible radiation in the X-ray region of the spectrum, for indicating the position of impact of the electron beam; and a layer of an electrically conductive and electron-permeable material deposited on said first and second portions, said layer being constructed so as to transmit the invisible X-radiation; in combination with index signal producing means positioned rearwardly of the target screen inside the tube so as to be impinged upon by said invisible X-radiation transmitted through said layer.

4. The combination of claim 3 wherein said first portion comprises a plurality of different color-producing phosphor strips configured in a repeating array, and said second portion comprises a plurality of strips of X-ray emitting material in register with the color-producing phosphor strips.

5. In combination: a beam-index cathode ray tube with an electron gun for providing a scannable electron beam and a target screen comprising: a first plurality of electron-sensitive strip-like portions which emit radiant energy in response to excitation by the scannable electron beam; and in registry therewith a second plurality of electron-sensitive strip-like portions which emit X-rays in response to bombardment by the electron beam thereby to indicate the position of impact on the target screen of the electron beam; and index signal deriving means responsive to the intensity of said X-rays for signalling the position of the electron beam; wherein the strip-like X-ray emitting portions are comprised of electrically conductive material mounted in juxtaposition with said first plurality of strip-like portions thereby to also provide the operating voltage for the target screen.

6. The combination of claim 5 including electrically insulating strands arranged in a mesh-like configuration with respect to the strips of electrically conductive material.

7. The combination of claim 5 wherein the first plurality of strip-like portions comprises different color-producing phosphors configured to form a repeating array of color-producing strips.

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