US3764841A - Magnetic shielding and x-ray image intensifier tube using same - Google Patents

Magnetic shielding and x-ray image intensifier tube using same Download PDF

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US3764841A
US3764841A US00171892A US3764841DA US3764841A US 3764841 A US3764841 A US 3764841A US 00171892 A US00171892 A US 00171892A US 3764841D A US3764841D A US 3764841DA US 3764841 A US3764841 A US 3764841A
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tube
coating
pump
envelope
layer
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W Coon
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
    • H01J29/94—Selection of substances for gas fillings; Means for obtaining or maintaining the desired pressure within the tube, e.g. by gettering
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
    • H01J29/02—Electrodes; Screens; Mounting, supporting, spacing or insulating thereof
    • H01J29/06—Screens for shielding; Masks interposed in the electron stream
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J31/00—Cathode ray tubes; Electron beam tubes
    • H01J31/08—Cathode ray tubes; Electron beam tubes having a screen on or from which an image or pattern is formed, picked up, converted, or stored
    • H01J31/50—Image-conversion or image-amplification tubes, i.e. having optical, X-ray, or analogous input, and optical output
    • H01J31/501—Image-conversion or image-amplification tubes, i.e. having optical, X-ray, or analogous input, and optical output with an electrostatic electron optic system

Definitions

  • the shell of soft iron surrounding the pump was inadequate to reduce the stray magnetic field within the interior of the intensifier tube to an acceptable level.
  • the magnet of the appendage pump produces a magnetic field of 700 gauss within the pump.
  • the stray field within the intensifier tube is reduced to a level of approximately five gauss.
  • five gauss is generally an unacceptable level.
  • Attempts have been made to surround certain portions of the intensifier tube with'sheets of highly magnetic permeable material to further reduce the stray magnetic field within the intensifier tube.
  • due to the relatively complex compound curves of the envelope in the region of the pump it was exceedingly difficult to form the sheet metal shielding material to the required configuration.
  • the principal object of the present invention is the provision of an improved magnetic shield and x-ray binder.
  • the exte- 1 rior of an evacuated electron tube is painted with a material which bonds to the envelope and which will form a particle binder coating.
  • a quantity of magnetic particles are sprinkled onto the coating of binder material while the binder material is still wet to embed the magnetic particles in the coating to form a magnetic shield conforming exactly to the shape of the exterior surface of the tube.
  • a magnetic shielding coating is formed on the exterior of an evacuated electron tube by painting the exterior portion of the tube with a rubber based paint and embedding a quantity of magnetic particles in the rubber based paint while wet.
  • FIG. 1 is a longitudinal sectional line diagram, partly schematic, depicting an x-ray image intensifier tube incorporating features of the present invention
  • FIG. 2 is an end view of the structure of FIG. 1 taken along line 2-2 in the direction of the arrows, and
  • FIG. 3 is an enlarged view of the structure of FIG. 2 taken along line 3-3 in the direction of the arrows with certain portions of the appendage pump and shield structure removed to show the magnetic coating.
  • FIG. 1 there is shown a longitudinal sectional view of an x -rayimage intensifier tube 1 incorporating features of the present invention.
  • the intensifier tube 1 includes an evacuated cylindrical envelope 2, as of glass, having a spherically convex input face 3, as of glass or aluminum, disposed to receive an x-ray image passing through the input face 3 to a similarly curved x-ray converter/screen or scintillator 4 disposed adjacent the input face 3 on the inside of the envelope 2.
  • the x-ray image converter screen 4 comprises an x-ray sensitive phosphor layer which converts the x-ray image into a photon image.
  • a photocathode layer is also includedin the screen 4 to receive the photon image and to convert same into an electron image which is emitter from the surface of the photocathode layer into the evacuated tube 2.
  • the electron images are embodied in the stream of electrons emitted from the x-ray converter screen 4.
  • the stream of electrons is accelerated and focused by means of a series of convergent electrostatic focusing lens structures 5 through a hollow cylindrical anode electrode 6 onto a cathode illuminescent intensifier screen 7 which converts the electron image into an intensified photon image for viewing by an operator or for use by photodetector equipment, not shown.
  • a source of potential 8 supplies the various operating potentials'to the electrodes 5, anode6, and fluorescent screen 7, the latter of which operates at anode potential.
  • the evelope 2 is evacuated to a relatively low pressure, as of 10" torr, by means of an appendage magnetically confined glow discharge getter-ion vacuum pump 9 (FIG. 2) of conventional design.
  • the appendage vacuum pump9 is connected in gas communication with the envelope 2 via a pump tubulation 11, as of glass, (see FIG. 3).
  • the pump tubulation 11 is generally of cylindrical configuration and closed at its outer end via a transverse end wall 12.
  • a collar 13 of magnetic material such as iron is bonded around the pump tubulation 11 to form one pole piece of the magnet structure of the appendage pump 9.
  • a hollow cylindrical magnet 14 (see FIG.
  • Two clam-shell shaped sheets of magnetic ally permeable material, such as soft iron, are fitted around the appendage pump 9 to reduce the stray magnetic field produced by'the magnet of the pump 9.
  • a clamshell shield 15 of mild steel approximately 0.060 inches thick reduces the stray magnetic field within the envelope 2 of the image intensifier tube 1 to approximately five gauss.
  • a five gauss stray magnetic field within the image intensifier tube allows only a resolution in the intensified image of approximately 40 lines or wires per inch. This is generally unacceptable for high resolution applications and it is desired to reduce the stray magnetic field to values which are substantially lower than five gauss.
  • a coating of magnetic material 16 shown by cross hatching in FIG. 3, is painted or otherwise formed on the exterior surface of the envelope 2 in the region immediately adjacent and facing the pump 9. The coating 16 extends part way up the exhaust tubulation 11. The coating further shields the interior of the envelope 2 from the stray magnetic field of the appendage pump 9.
  • the coating of magnetic permeable material 16 is applied by painting the cross hatched portion of the envelope 2 with a first layer of a rubber based paint, such as Dow Corning type 92-009 rubber paint (dispersion coating). While the paint is still wet, iron particles of approximately 60 mesh or smaller are sprinkled onto the layer of rubber paint to embed the iron powder in the rubber coating. Upon drying, the excess iron particles are dusted from the coating. Two additional layers of exactly the same configuration are successively painted onto the coated area 16 to an overall thickness of approximately 0.015 inch. A final overcoat of rubber base paint is applied to improve the appearance of the coating.
  • a rubber based paint such as Dow Corning type 92-009 rubber paint (dispersion coating). While the paint is still wet, iron particles of approximately 60 mesh or smaller are sprinkled onto the layer of rubber paint to embed the iron powder in the rubber coating. Upon drying, the excess iron particles are dusted from the coating. Two additional layers of exactly the same configuration are successively painted onto the coated area 16 to an overall thickness of approximately 0.015 inch. A final
  • the resultant magnetic shield coating 16 greatly reduces the intensity of the stray magnetic field within the tube. More particularly, the aforedescribed coating 16 reduced the stray magnetic field within the envelope 2 from five gauss to approximately 0.25 gauss, resulting in an increase in resolution of the imageintensifier tube from approximately 40 lines per inch to lines per inch.
  • the magnetic coating 16 of the present invention greatly facilitates magnetic shielding of the image intensifier tube as the coating exactly matches the compound curves of the glass surface of the envelope 2, thereby minimizing the possiblity of leakage of magnetic field around or through the shield.
  • An evacuated electron tube comprising a nonmagnetic envelope containing anode and cathode electrode structures and a magnetically-permeable coating on at least a portion of said envelope for shielding an adjacent interior portion of said envelope from external magnetic fields,
  • said coating comprises a layer of a binder material on said portion of said envelope and a layer of magnetically-permeable particles embedded in the surface of said layer of binder material wherein said portion of said envelope has a plurality of said coatings formed thereover in successive layers, each coating comprising a layer of said binder material and a layer of said magnetically-permeable particles embedded in the surface of said layer of binder material, thereby to provide increased shielding for said tube.
  • each layer of binder material is a rubber-based paint and each layer of magnetically-permeable particles is iron.
  • the tube of claim 1 further including a coating of binder material over said plurality of said coating.
  • said covering comprises a plurality of coatings formed in succession over said portion of said envelope, each coating comprising a layer of a binder material and a layer of magneticallypermeable particles embedded in the surface of said layer of binder material, whereby said plurality of coatings provide increased shielding for said tube.

Abstract

An x-ray image intensifier tube is evacuated by means of an appendage magnetically confined glow discharge getter-ion vacuum pump. A shell of soft iron is disposed surrounding the magnet of the appendage pump for shielding the image intensifier tube from the stray magnetic field of the appendage pump. A coating of magnetic material on the envelope of the intensifier tube, in the region facing the pump, provides additional magnetic shielding for shielding the interior of the tube from the stray magnetic field of the pump to further improve the resolution of the image intensifier tube.

Description

United'States Patent [191 Coon Oct. 9, 1973 [54] MAGNETIC SHIELDING FOR EVACUATED TUBE COMPRISING PLURAL COATING OF BINDER AND MAGNETIC PARTICLES [76] lnventor: Warren P. Coon, 3126 McKinley Dr, Santa Clara, Calif.
[22] Filed: Aug. 16, 1971 21 Appl. No.: 171,892
[52] US. Cl. 313/153, 315/8 [51] Int. Cl. H011 29/06 [58] Field of Search 117/234, 235, 239,
[56] References Cited UNITED STATES PATENTS 3,443,138 5/1969 Schwartz 315/8 2,895,851 7/1959 Johnson 117/235 2,532,876 12/1950 Asche et al. 335/303 Primary ExaminerRoy Lake Assistant Examiner-Darwin R. l-lostetter Attorney-Stanley Z. Cole [57] ABSTRACT 3 Claims, 3 Drawing Figures PAItNTEll "E 9 I975 INVENTOR. WARREN P. COON.
ATTORNEY MAGNETIC SI'IIELDING FOR EVACUATED TUBE COMPRISING PLURAL COATING OF BINDER ANI) MAGNETIC PARTICLES DESCRIPTION OFTl-IE PRIOR ART l-leretofore, magnetically confined glow discharge getter-ion vaccum pumps have been appended to x-ray image intensifier tubes for maintaining a relatively high vacuum within the intensifier tube. A clam shell shaped shield of soft iron was disposed surrounding the magnet of the appendage pump to shield the interior of the intensifier tube from the stray magnetic field produced by the magnet of the pump.
However, it was found that the shell of soft iron surrounding the pump was inadequate to reduce the stray magnetic field within the interior of the intensifier tube to an acceptable level. In a typical example, the magnet of the appendage pump produces a magnetic field of 700 gauss within the pump. With the soft iron shielding shell in place, the stray field within the intensifier tube is reduced to a level of approximately five gauss. However, five gauss is generally an unacceptable level. Attempts have been made to surround certain portions of the intensifier tube with'sheets of highly magnetic permeable material to further reduce the stray magnetic field within the intensifier tube. However, due to the relatively complex compound curves of the envelope in the region of the pump it was exceedingly difficult to form the sheet metal shielding material to the required configuration. As a result, imperfect shielding was obtained. Therefore, it is desired to obtain an improved method and apparatus for shielding image intensifier tubes which will allow the magnetic shielding material to conform exactly to the complex curves found on the exterior of the intensifier tube in the region of the appendage pump.
SUMMARY OF THE PRESENT INVENTIO The principal object of the present invention is the provision of an improved magnetic shield and x-ray binder.
In another feature of the present invention, the exte- 1 rior of an evacuated electron tube is painted with a material which bonds to the envelope and which will form a particle binder coating. A quantity of magnetic particles are sprinkled onto the coating of binder material while the binder material is still wet to embed the magnetic particles in the coating to form a magnetic shield conforming exactly to the shape of the exterior surface of the tube.
In another feature of the present invention, a magnetic shielding coating is formed on the exterior of an evacuated electron tube by painting the exterior portion of the tube with a rubber based paint and embedding a quantity of magnetic particles in the rubber based paint while wet.
Other features and advantages of the present invention will become apparent upon a perusal of the following specification taken in connection with the accompanying drawing, wherein:
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional line diagram, partly schematic, depicting an x-ray image intensifier tube incorporating features of the present invention,
FIG. 2 is an end view of the structure of FIG. 1 taken along line 2-2 in the direction of the arrows, and
FIG. 3 is an enlarged view of the structure of FIG. 2 taken along line 3-3 in the direction of the arrows with certain portions of the appendage pump and shield structure removed to show the magnetic coating.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, there is shown a longitudinal sectional view of an x -rayimage intensifier tube 1 incorporating features of the present invention. The intensifier tube 1 includes an evacuated cylindrical envelope 2, as of glass, having a spherically convex input face 3, as of glass or aluminum, disposed to receive an x-ray image passing through the input face 3 to a similarly curved x-ray converter/screen or scintillator 4 disposed adjacent the input face 3 on the inside of the envelope 2.
The x-ray image converter screen 4 comprises an x-ray sensitive phosphor layer which converts the x-ray image into a photon image. A photocathode layer is also includedin the screen 4 to receive the photon image and to convert same into an electron image which is emitter from the surface of the photocathode layer into the evacuated tube 2.
The electron images are embodied in the stream of electrons emitted from the x-ray converter screen 4. The stream of electrons is accelerated and focused by means of a series of convergent electrostatic focusing lens structures 5 through a hollow cylindrical anode electrode 6 onto a cathode illuminescent intensifier screen 7 which converts the electron image into an intensified photon image for viewing by an operator or for use by photodetector equipment, not shown. A source of potential 8 supplies the various operating potentials'to the electrodes 5, anode6, and fluorescent screen 7, the latter of which operates at anode potential.
The evelope 2 is evacuated to a relatively low pressure, as of 10" torr, by means of an appendage magnetically confined glow discharge getter-ion vacuum pump 9 (FIG. 2) of conventional design. The appendage vacuum pump9 is connected in gas communication with the envelope 2 via a pump tubulation 11, as of glass, (see FIG. 3). The pump tubulation 11 is generally of cylindrical configuration and closed at its outer end via a transverse end wall 12. A collar 13 of magnetic material such as iron is bonded around the pump tubulation 11 to form one pole piece of the magnet structure of the appendage pump 9. A hollow cylindrical magnet 14 (see FIG. 2) is disposed around the tubulation 11 and butts at one end with the collar 13 and at the other end it is generally flush with the closing end wall 12 of the exhaust tube 11. A disc of magnetic material, not shown, is disposed across the outer end of the magnet for fonn the second pole piece of the magnet. Anode and cathode pump electrodes are disposed within the exhaust tube 11. The magnet structure produces an axial magnetic field of approximately 700 gauss within the appendagepump for confining the glow discharge therein.
Two clam-shell shaped sheets of magnetic ally permeable material, such as soft iron, are fitted around the appendage pump 9 to reduce the stray magnetic field produced by'the magnet of the pump 9. A clamshell shield 15 of mild steel approximately 0.060 inches thick reduces the stray magnetic field within the envelope 2 of the image intensifier tube 1 to approximately five gauss.
A five gauss stray magnetic field within the image intensifier tube allows only a resolution in the intensified image of approximately 40 lines or wires per inch. This is generally unacceptable for high resolution applications and it is desired to reduce the stray magnetic field to values which are substantially lower than five gauss. Accordingly, a coating of magnetic material 16, shown by cross hatching in FIG. 3, is painted or otherwise formed on the exterior surface of the envelope 2 in the region immediately adjacent and facing the pump 9. The coating 16 extends part way up the exhaust tubulation 11. The coating further shields the interior of the envelope 2 from the stray magnetic field of the appendage pump 9.
In a preferred embodiment, the coating of magnetic permeable material 16 is applied by painting the cross hatched portion of the envelope 2 with a first layer of a rubber based paint, such as Dow Corning type 92-009 rubber paint (dispersion coating). While the paint is still wet, iron particles of approximately 60 mesh or smaller are sprinkled onto the layer of rubber paint to embed the iron powder in the rubber coating. Upon drying, the excess iron particles are dusted from the coating. Two additional layers of exactly the same configuration are successively painted onto the coated area 16 to an overall thickness of approximately 0.015 inch. A final overcoat of rubber base paint is applied to improve the appearance of the coating.
The resultant magnetic shield coating 16 greatly reduces the intensity of the stray magnetic field within the tube. More particularly, the aforedescribed coating 16 reduced the stray magnetic field within the envelope 2 from five gauss to approximately 0.25 gauss, resulting in an increase in resolution of the imageintensifier tube from approximately 40 lines per inch to lines per inch.
The magnetic coating 16 of the present invention greatly facilitates magnetic shielding of the image intensifier tube as the coating exactly matches the compound curves of the glass surface of the envelope 2, thereby minimizing the possiblity of leakage of magnetic field around or through the shield.
What is claimed is:
1. An evacuated electron tube comprising a nonmagnetic envelope containing anode and cathode electrode structures and a magnetically-permeable coating on at least a portion of said envelope for shielding an adjacent interior portion of said envelope from external magnetic fields,
characterized in that said coating comprises a layer of a binder material on said portion of said envelope and a layer of magnetically-permeable particles embedded in the surface of said layer of binder material wherein said portion of said envelope has a plurality of said coatings formed thereover in successive layers, each coating comprising a layer of said binder material and a layer of said magnetically-permeable particles embedded in the surface of said layer of binder material, thereby to provide increased shielding for said tube.
2. The tube of claim 1 wherein each layer of binder material is a rubber-based paint and each layer of magnetically-permeable particles is iron.
3. The tube of claim 1 further including a coating of binder material over said plurality of said coating.
" UNITED Sl 'A'l'hb PALM Utklblb CER'HFICATE OF CORECTION Patent No 3 764 841 Dated 1973 October 9 Inventor(s) Coon, Warren H.
It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
In the title, change "COATING" to ---COATINGS- On the Abstract page, add the following:
-[73] Assignees Varian' Associates, a corporation of California. Q
In claim 1, change lines 7 to 17 to read as follows:
--characterized in that said covering comprises a plurality of coatings formed in succession over said portion of said envelope, each coating comprising a layer of a binder material and a layer of magneticallypermeable particles embedded in the surface of said layer of binder material, whereby said plurality of coatings provide increased shielding for said tube.--
Signed and sealed this 12th day of February 1974.
(SEAL) Attest: m w t H EDWARD M.FLETCHER,JR. I C. MARSHALL DANN Attesting Officer Commissioner of Patents

Claims (3)

1. An evacuated electron tube comprising a non-magnetic envelope containing anode and cathode electrode structures and a magnetically-permeable coating on at least a portion of said envelope for shielding an adjacent interior portion of said envelope from external magnetic fields, characterized in that said covering comprises a plurality of coatings formed in succession over said portion of said envelope, each coating comprising a layer of a binder material and a layer of magnetically-permeable particles embedded in the surface of said layer of binder material, whereby said plurality of coatings provide increased shielding for said tube.
2. The tube of claim 1 wherein each layer of binder material is a rubber-based paint and each layer of magnetically-permeable particles is iron.
3. The tube of claim 1 further including a coating of binder material over said plurality of said coating.
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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6297489B1 (en) * 1996-05-02 2001-10-02 Hamamatsu Photonics K.K. Electron tube having a photoelectron confining mechanism
CN112885686A (en) * 2021-01-14 2021-06-01 北方夜视技术股份有限公司 Anti-electromagnetic interference tube shell electromagnetic shielding layer of image intensifier and preparation method thereof

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2532876A (en) * 1946-12-19 1950-12-05 Asche Robert Electromagnetic artificial muscle
US2895851A (en) * 1955-08-18 1959-07-21 Abrasive Company Of America Magnetic application of paramagnetic spray paint
US3443138A (en) * 1966-11-08 1969-05-06 Nat Video Corp Magnetic shielding means for cathode ray tube

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2532876A (en) * 1946-12-19 1950-12-05 Asche Robert Electromagnetic artificial muscle
US2895851A (en) * 1955-08-18 1959-07-21 Abrasive Company Of America Magnetic application of paramagnetic spray paint
US3443138A (en) * 1966-11-08 1969-05-06 Nat Video Corp Magnetic shielding means for cathode ray tube

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6297489B1 (en) * 1996-05-02 2001-10-02 Hamamatsu Photonics K.K. Electron tube having a photoelectron confining mechanism
CN112885686A (en) * 2021-01-14 2021-06-01 北方夜视技术股份有限公司 Anti-electromagnetic interference tube shell electromagnetic shielding layer of image intensifier and preparation method thereof
CN112885686B (en) * 2021-01-14 2023-04-11 北方夜视技术股份有限公司 Anti-electromagnetic interference tube shell electromagnetic shielding layer of image intensifier and preparation method thereof

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