EP0851455A1 - Radiological image intensifier tube - Google Patents

Radiological image intensifier tube Download PDF

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Publication number
EP0851455A1
EP0851455A1 EP97403143A EP97403143A EP0851455A1 EP 0851455 A1 EP0851455 A1 EP 0851455A1 EP 97403143 A EP97403143 A EP 97403143A EP 97403143 A EP97403143 A EP 97403143A EP 0851455 A1 EP0851455 A1 EP 0851455A1
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Prior art keywords
layer
electrons
screen
tube
phosphors
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EP97403143A
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German (de)
French (fr)
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EP0851455B1 (en
Inventor
Yvan Raverdy
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Thales Electron Devices SA
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Thomson Tubes Electroniques
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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
    • H01J29/02—Electrodes; Screens; Mounting, supporting, spacing or insulating thereof
    • H01J29/10—Screens on or from which an image or pattern is formed, picked up, converted or stored
    • H01J29/18—Luminescent screens
    • H01J29/28—Luminescent screens with protective, conductive or reflective layers
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21K—TECHNIQUES FOR HANDLING PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
    • G21K4/00—Conversion screens for the conversion of the spatial distribution of X-rays or particle radiation into visible images, e.g. fluoroscopic screens
    • 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
    • H01J29/10—Screens on or from which an image or pattern is formed, picked up, converted or stored
    • H01J29/18—Luminescent screens
    • H01J29/185—Luminescent screens measures against halo-phenomena
    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21K—TECHNIQUES FOR HANDLING PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
    • G21K4/00—Conversion screens for the conversion of the spatial distribution of X-rays or particle radiation into visible images, e.g. fluoroscopic screens
    • G21K2004/04—Conversion screens for the conversion of the spatial distribution of X-rays or particle radiation into visible images, e.g. fluoroscopic screens with an intermediate layer

Definitions

  • the invention relates to image intensifier tubes.
  • the luminescent observation screen of the IIR tube has the role of generate a visible light image when the screen is excited by a electron beam hitting its photoluminescent surface.
  • the invention relates more particularly to the luminescent observation screen comprising means to improve the contrast of the image.
  • Image intensifier tubes are vacuum tubes including an entry screen, located at the front of the tube, an optical system electronic, and an image observation screen located at the rear of the tube, side of an exit window from the latter.
  • the screen input also has a scintillator screen that converts x photons visible photon incidents.
  • Visible photons excite a photocathode which in response generates a flow of electrons.
  • This flow of electrons is then transmitted by a electronic optics system that focuses electrons, and directs them on the observation screen.
  • the observation screen has one or more layers of luminophore grains deposited on a glass support transparent. The phosphors struck by the electrons then produce visible light from the outside of the tube through the transparent support.
  • Figure 1 schematically shows such an intensifier tube image of the radiological type.
  • the intensifier tube 1 comprises a glass envelope 2 one end of which, at the front of the tube, is closed by an inlet window 3, exposed to x-ray radiation.
  • the second end of the envelope forming the back of the tube is closed by the observation screen 4 transparent to light.
  • X-rays are converted into light rays by a screen scintillator 5.
  • the light rays excite a photocathode 6 which response produces electrons.
  • These electrons are extracted from the photocathode 6 and accelerated to the observation screen 4 using different electrodes 7, and an anode 8 arranged along an axis longitudinal 9 of the tube and which form the electronic optical system.
  • the observation screen 4 is formed by a transparent piece of glass attached tightly to the envelope 2. This piece of glass further constitutes in the example shown, a support which carries phosphors 10, for example.
  • establishing the acceleration potential of electrons from the photocathode of the tube is performed by a grid under voltage acceleration located near the observation screen. Electrons accelerated cross the grid reaching the phosphors 10, from the screen of observation, which produce visible light.
  • the acceleration potential is obtained by a voltage applied to a thin layer of conductive material, by example a metal deposited directly on the phosphor layer of the observation screen.
  • a metal deposited directly on the phosphor layer of the observation screen The small thickness of this metal layer allows the passage without significant loss of electrons to the phosphors.
  • the thickness of the metal layer for example in aluminum, is around 0.3 micrometer.
  • This thickness very small, is chosen so that the layer is transparent to electrons, so that they reach the photocathode without losses.
  • Aluminum is not naturally transparent to electrons except in very small thickness.
  • spoke tubes cathodic and not for radiological image intensifier tubes cover the aluminum layer with a carbon layer to limit the production of secondary electrons by the phosphor layer.
  • the carbon is indeed a material with a very low emission coefficient secondary, which therefore does not generate too many secondary electrons when it is struck by the electrons of the incident beam, and which is also relatively transparent for these incident electrons (high energy) but which is absorbing for the secondary electrons which would be emitted by the layer of phosphorous.
  • the backscatter electrons represent around 20% of the incident electron beam Ei, parasitizing strongly the image produced by the observation screen.
  • the electrons of backscatter are dispersed during their emission inside the tube and when they fall back on the observation screen, accelerated by the tensions polarization of the tube, these backscatter electrons, excite totally distributed, the phosphors of the observation screen.
  • This secondary phenomenon produces background noise, resulting in decrease in image contrast.
  • the invention proposes an IIR tube comprising a vacuum electronic tube and a luminescent observation screen (20), the screen having a support glass on which a layer of phosphors is deposited, the observation screen producing a bright image when the phosphors are excited by an electron beam, and the layer of phosphors being covered with a layer of aluminum, characterized in that the aluminum layer has a thickness of at least 1 micrometer in the aim of reducing on the one hand the quantity of electrons re-emitted from the screen observation towards the tube and on the other hand the proportion of these electrons which come back to strike the layer of phosphors.
  • the aluminum layer will act as an electron filter for backscatter, by first absorbing electrons from backscatter when at the time of their generation by the impact of the beam of incident electrons Ei on the phosphors, they cross the layer of aluminum in the opposite direction to that of the incident electron beam and by absorbing other backscatter electrons a second time, when they cross the same layer of aluminum again when they fall towards the observation screen, in the direction of the incident electrons.
  • the aluminum layer is in the form of a coating deposited, in principle directly on the phosphors of the screen of observation but which could possibly be on a support located in the path of incident electrons near the observation screen.
  • the coating also fulfills the function of establishing the potential for electron acceleration over the entire surface of the phosphors, what is necessary in the case of the tube observation screen image intensifiers.
  • the thickness of the aluminum layer is preferably included between 1 and 3 micrometers. A value of 1.5 to 2 micrometers is very suitable good.
  • the aluminum layer can also be separated, with a small distance, phosphors, by the vacuum of the tube, in this case the coating is supported by a thin grid.
  • An incident electron beam Ei crosses with a loss of electrons, the aluminum layer 30, in an area A1 of the screen of observation and excites the layers of phosphors 28 producing a light emission h1, visible through the support glass 22, and backscatter electrons Er1, Er2, Across Ern ,.
  • These backscatter electrons, generated by the phosphors, are returned to the inside of the tube and are found to be partially absorbed, a first time, by crossing the layer aluminum 30, in their displacement towards the inside of the tube, then find again partially absorbed a second time, falling back on the observation screen, attracted by the bias potential applied to the aluminum layer.
  • the reduction of the electrons backscatter absorbed by this aluminum layer leads to a noticeable improvement in image contrast.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Image-Pickup Tubes, Image-Amplification Tubes, And Storage Tubes (AREA)
  • Cathode-Ray Tubes And Fluorescent Screens For Display (AREA)

Abstract

A radiological image intensifier which produces a visible picture from incident X-rays includes an evacuated electron tube with a luminescent display screen (20) at one end on which electrons from a scintillator at the other end impinge. Screen (20) comprises a glass support (22) carrying a layer of luminescent material (28) covered by a layer of aluminium (30) at least 1 micron thick which is designed to inhibit the re-emission of electrons from the screen back into the tube and the impact on the screen of such electrons as are re-emitted.

Description

L'invention concerne les tubes intensificateurs d'image radiologique (tube IIR) utilisant un tube électronique à vide et un écran d'observation luminescent.The invention relates to image intensifier tubes. radiological (IIR tube) using an electronic vacuum tube and a screen luminescent observation.

L'écran d'observation luminescent du tube IIR a pour rôle de générer une image lumineuse visible, lorsque l'écran est excité par un faisceau d'électrons frappant sa surface photoluminescente. L'invention concerne plus particulièrement l'écran d'observation luminescent comportant des moyens pour améliorer le contraste de l'image.The luminescent observation screen of the IIR tube has the role of generate a visible light image when the screen is excited by a electron beam hitting its photoluminescent surface. The invention relates more particularly to the luminescent observation screen comprising means to improve the contrast of the image.

Les tubes intensificateurs d'image sont des tubes à vide comprenant un écran d'entrée, situé à l'avant du tube, un système d'optique électronique, et un écran d'observation de l'image situé à l'arrière du tube, du côté d'une fenêtre de sortie de ce dernier.Image intensifier tubes are vacuum tubes including an entry screen, located at the front of the tube, an optical system electronic, and an image observation screen located at the rear of the tube, side of an exit window from the latter.

Dans les tubes intensificateurs d'image radiologique, l'écran d'entrée comporte en outre un écran scintillateur qui convertit les photons x incidents en photons visibles.In X-ray image intensifier tubes, the screen input also has a scintillator screen that converts x photons visible photon incidents.

Les photons visibles excitent une photocathode qui en réponse génère un flux d'électrons. Ce flux d'électrons est ensuite transmis par un système d'optique électronique qui focalise les électrons, et les dirige sur l'écran d'observation. L'écran d'observation comporte une ou plusieurs couches de grains luminophores déposée sur un support en verre transparent. Les luminophores frappés par les électrons produisent alors de la lumière visible de l'extérieur du tube à travers le support transparent.Visible photons excite a photocathode which in response generates a flow of electrons. This flow of electrons is then transmitted by a electronic optics system that focuses electrons, and directs them on the observation screen. The observation screen has one or more layers of luminophore grains deposited on a glass support transparent. The phosphors struck by the electrons then produce visible light from the outside of the tube through the transparent support.

La figure, 1 montre schématiquement un tel tube intensificateur d'image du type radiologique.Figure 1 schematically shows such an intensifier tube image of the radiological type.

Le tube intensificateur 1 comprend une enveloppe 2 en verre dont une extrémité, à l'avant du tube, est fermée par une fenêtre d'entrée 3, exposée à un rayonnement de photons x.The intensifier tube 1 comprises a glass envelope 2 one end of which, at the front of the tube, is closed by an inlet window 3, exposed to x-ray radiation.

La seconde extrémité de l'enveloppe formant l'arrière du tube est fermée par l'écran d'observation 4 transparent à la lumière.The second end of the envelope forming the back of the tube is closed by the observation screen 4 transparent to light.

Les rayons x sont convertis en rayons lumineux par un écran scintillateur 5. Les rayons lumineux excitent une photocathode 6 qui en réponse produit des électrons. Ces électrons sont extraits de la photocathode 6 et accélérés vers l'écran d'observation 4 à l'aide de différentes électrodes 7, et d'une anode 8 disposée le long d'un axe longitudinal 9 du tube et qui forment le système d'optique électronique.X-rays are converted into light rays by a screen scintillator 5. The light rays excite a photocathode 6 which response produces electrons. These electrons are extracted from the photocathode 6 and accelerated to the observation screen 4 using different electrodes 7, and an anode 8 arranged along an axis longitudinal 9 of the tube and which form the electronic optical system.

Dans l'exemple représenté, l'écran d'observation 4 est formé par une pièce transparente en verre rapportée de façon étanche à l'enveloppe 2. Cette pièce de verre constitue en outre dans l'exemple montré, un support qui porte des luminophores 10, par exemple.In the example shown, the observation screen 4 is formed by a transparent piece of glass attached tightly to the envelope 2. This piece of glass further constitutes in the example shown, a support which carries phosphors 10, for example.

Dans certaines réalisations de tubes à intensification d'image, l'établissement du potentiel d'accélération des électrons issus de la photocathode du tube est effectué par une grille sous la tension d'accélération disposée à proximité de l'écran d'observation. Les électrons accélérés traversent la grille atteignant les luminophores 10, de l'écran d'observation, qui produisent de la lumière visible.In some realizations of image intensification tubes, establishing the acceleration potential of electrons from the photocathode of the tube is performed by a grid under voltage acceleration located near the observation screen. Electrons accelerated cross the grid reaching the phosphors 10, from the screen of observation, which produce visible light.

Dans d'autres réalisations, le potentiel d'accélération est obtenu par une tension appliquée à une fine couche de matériau conducteur, par exemple un métal déposé directement sur la couche de luminophores de l'écran d'observation. La faible épaisseur de cette couche de métal permet le passage sans perte notable des électrons vers les luminophores. Dans les réalisations actuelles, l'épaisseur de la couche métallique, par exemple en aluminium, est de l'ordre de 0,3 micromètre.In other embodiments, the acceleration potential is obtained by a voltage applied to a thin layer of conductive material, by example a metal deposited directly on the phosphor layer of the observation screen. The small thickness of this metal layer allows the passage without significant loss of electrons to the phosphors. In the current achievements, the thickness of the metal layer, for example in aluminum, is around 0.3 micrometer.

Cette épaisseur, très faible, est choisie pour que la couche soit transparente aux électrons, afin que ces derniers atteignent la photocathode sans pertes. En effet, l'aluminium n'est pas naturellement transparent aux électrons sauf en très faible épaisseur.This thickness, very small, is chosen so that the layer is transparent to electrons, so that they reach the photocathode without losses. Aluminum is not naturally transparent to electrons except in very small thickness.

Par ailleurs, on a déjà proposé pour des tubes à rayons cathodiques et non pour des tubes intensificateurs d'image radiologique, de recouvrir la couche d'aluminium par une couche de carbone pour limiter la production d'électrons secondaires par la couche de luminophores. Le carbone est en effet un matériau à très faible coefficient d'émission secondaire, qui ne génère donc pas trop d'électrons secondaires lorsqu'il est frappé par les électrons du faisceau incident, et qui de plus est relativement transparent pour ces électrons incidents (de forte énergie) mais qui est absorbant pour les électrons secondaires qui seraient émis par la couche de phosphores. Furthermore, it has already been proposed for spoke tubes cathodic and not for radiological image intensifier tubes, cover the aluminum layer with a carbon layer to limit the production of secondary electrons by the phosphor layer. The carbon is indeed a material with a very low emission coefficient secondary, which therefore does not generate too many secondary electrons when it is struck by the electrons of the incident beam, and which is also relatively transparent for these incident electrons (high energy) but which is absorbing for the secondary electrons which would be emitted by the layer of phosphorous.

L'émission d'électrons secondaires est gênante pour la raison suivante. Dans les tubes intensificateurs d'images, les électrons accélérés issus de la photocathode, frappent la couche des luminophores provoquant une émission de photons dans le domaine de la lumière visible représentant l'image radiologique. Si l'on considère un faisceau d'électrons incidents Ei, (voir figure 1) frappant les luminophores dans une zone Z de l'écran d'observation, ces mêmes luminophores produisent à leur tour par l'impact des électrons incident Ei, des électrons réémis Er, se dirigeant vers l'intérieur du tube, puis retombant de nouveau sur les luminophores de l'écran d'observation, à un endroit qui n'est pas l'endroit où ils ont été émis. Ce phénomène parasite l'image initiale produite par le faisceau d'électrons incidents Ei. Par la suite nous appellerons ces électrons réémis, électrons de rétrodiffusion.The emission of secondary electrons is troublesome for the reason next. In image intensifier tubes, accelerated electrons from the photocathode, strike the layer of phosphors causing an emission of photons in the visible light domain representing the radiological image. If we consider an incident electron beam Ei, (see figure 1) striking the phosphors in an area Z of the screen of observation, these same phosphors in turn produce by the impact incident electrons Ei, reemitted electrons Er, moving inward of the tube, then falling again on the phosphors of the screen of observation, at a place which is not the place where they were emitted. This phenomenon parasitizes the initial image produced by the electron beam Ei incidents. Thereafter we will call these reemitted electrons, electrons of backscatter.

Dans les réalisations actuelles les électrons de rétrodiffusion représentent environ 20% du faisceau d'électrons incidents Ei, parasitant fortement l'image produite par l'écran d'observation. Les électrons de rétrodiffusion se trouvent dispersés lors de leur émission à l'intérieur du tube et lorsqu'ils retombent sur l'écran d'observation, accélérés par les tensions de polarisation du tube, ces électrons de rétrodiffusion, viennent exciter de manière totalement répartie, les luminophores de l'écran d'observation. Ce phénomène secondaire produit un bruit de fond, se traduisant par une diminution du contraste de l'image.In current realizations the backscatter electrons represent around 20% of the incident electron beam Ei, parasitizing strongly the image produced by the observation screen. The electrons of backscatter are dispersed during their emission inside the tube and when they fall back on the observation screen, accelerated by the tensions polarization of the tube, these backscatter electrons, excite totally distributed, the phosphors of the observation screen. This secondary phenomenon produces background noise, resulting in decrease in image contrast.

D'une manière inattendue, on s'est aperçu qu'on pouvait obtenir un résultat aussi bon sans déposer de couche de carbone, en utilisant uniquement les propriétés de l'aluminium et en choisissant une épaisseur de couche d'aluminium bien supérieure à ce qu'on devrait normalement choisir compte-tenu de la faible transparence de ce matériau aux électrons.Unexpectedly, we realized that we could get such a good result without depositing a carbon layer, using only the properties of aluminum and choosing a thickness of aluminum layer far superior to what one would normally choose given the low transparency of this material to electrons.

Il se trouve que l'aluminium a un coefficient d'émission secondaire suffisamment faible pour jouer en partie le même rôle que la couche de carbone. La couche d'aluminium peut alors constituer une couche unique de revêtement des luminophores. La fabrication du tube IIR s'en trouve simplifiée.It turns out that aluminum has a secondary emission factor weak enough to play in part the same role as the layer of carbon. The aluminum layer can then constitute a single layer of coating of phosphors. The manufacturing of the IIR tube is found simplified.

C'est pourquoi, l'invention propose un tube IIR comportant un tube électronique à vide et un écran d'observation luminescent (20), l'écran ayant un verre support sur lequel est déposée une couche de luminophores, l'écran d'observation produisant une image lumineuse lorsque les luminophores sont excités par un faisceau d'électrons, et la couche de luminophores étant recouverte d'une couche d'aluminium, caractérisé en ce que la couche d'aluminium a une épaisseur d'au moins 1 micromètre dans le but de réduire d'une part la quantité d'électrons réémis de l'écran d'observation vers le tube et d'autre part la proportion de ces électrons qui reviennent frapper la couche de luminophores.This is why, the invention proposes an IIR tube comprising a vacuum electronic tube and a luminescent observation screen (20), the screen having a support glass on which a layer of phosphors is deposited, the observation screen producing a bright image when the phosphors are excited by an electron beam, and the layer of phosphors being covered with a layer of aluminum, characterized in that the aluminum layer has a thickness of at least 1 micrometer in the aim of reducing on the one hand the quantity of electrons re-emitted from the screen observation towards the tube and on the other hand the proportion of these electrons which come back to strike the layer of phosphors.

La couche d'aluminium va jouer le rôle de filtre d'électrons de rétrodiffusion, en absorbant une première fois, des électrons de rétrodiffusion lorsque au moment de leur génération par l'impact du faisceau d'électrons incidents Ei sur les luminophores, ils traversent la couche d'aluminium dans le sens opposé à celui du faisceau d'électrons incidents et en absorbant une seconde fois d'autres électrons de rétrodiffusion, lorsqu'ils traversent de nouveau la même couche d'aluminium lors de leur retombée vers l'écran d'observation, dans le sens des électrons incidents.The aluminum layer will act as an electron filter for backscatter, by first absorbing electrons from backscatter when at the time of their generation by the impact of the beam of incident electrons Ei on the phosphors, they cross the layer of aluminum in the opposite direction to that of the incident electron beam and by absorbing other backscatter electrons a second time, when they cross the same layer of aluminum again when they fall towards the observation screen, in the direction of the incident electrons.

La couche d'aluminium se présente sous la forme d'un revêtement déposé, en principe directement sur les luminophores de l'écran d'observation mais qui pourrait eventuellement être sur un support situé dans le trajet des électrons incidents à proximité de l'écran d'observation.The aluminum layer is in the form of a coating deposited, in principle directly on the phosphors of the screen of observation but which could possibly be on a support located in the path of incident electrons near the observation screen.

Le revêtement remplit aussi la fonction d'établissement du potentiel d'accélération des électrons sur toute la surface des luminophores, ce qui est nécessaire dans le cas de l'écran d'observation des tubes intensificateurs d'image.The coating also fulfills the function of establishing the potential for electron acceleration over the entire surface of the phosphors, what is necessary in the case of the tube observation screen image intensifiers.

L'épaisseur de la couche d'aluminium est de préférence comprise entre 1 et 3 micromètres. Une valeur de 1,5 à 2 micromètres convient très bien.The thickness of the aluminum layer is preferably included between 1 and 3 micrometers. A value of 1.5 to 2 micrometers is very suitable good.

La couche d'aluminium peut être aussi séparée, d'une faible distance, des luminophores, par le vide du tube, dans ce cas le revêtement est supporté par une grille de faible épaisseur.The aluminum layer can also be separated, with a small distance, phosphors, by the vacuum of the tube, in this case the coating is supported by a thin grid.

D'autres caractéristiques et avantages de l'invention apparaítront à la lecture de la description détaillée et qui est faite en référence aux dessins annexés dans lesquels :

  • la figure 1, déjà décrite, représente la structure d'un tube intensificateur d'images selon l'art antérieur.
  • la figure 2 représente un exemple de réalisation d'un écran d'observation du tube intensificateur d'image pour radiologie de la figure 1. Un écran d'observation 20 comporte :
  • un verre support 22 transparent à la lumière, fermant hermétiquement la partie inférieure du tube, non représentée sur la figure. Le verre support comporte une face interne 24, située à l'intérieur du tube et une face externe 26 au tube permettant l'observation de l'image générée par l'écran d'observation.
  • des couches de luminophores 28, déposées sur la face interne 24 du verre support.
  • une couche d'aluminium 30 d'environ 2 micromètres d'épaisseur, déposée sur les couches de luminophores 28. Un potentiel d'accélération des électrons est appliqué à cette couche d'aluminium.
Other characteristics and advantages of the invention will appear on reading the detailed description which is made with reference to the accompanying drawings in which:
  • Figure 1, already described, shows the structure of an image intensifier tube according to the prior art.
  • FIG. 2 represents an exemplary embodiment of an observation screen of the image intensifier tube for radiology of FIG. 1. An observation screen 20 comprises:
  • a support glass 22 transparent to light, hermetically closing the lower part of the tube, not shown in the figure. The support glass has an internal face 24, located inside the tube and an external face 26 to the tube allowing the observation of the image generated by the observation screen.
  • layers of phosphors 28, deposited on the internal face 24 of the support glass.
  • an aluminum layer 30 of approximately 2 micrometers thick, deposited on the phosphor layers 28. A potential for electron acceleration is applied to this aluminum layer.

Un faisceau d'électrons incidents Ei, traverse avec une perte d'électrons, la couche d'aluminium 30, dans une zone A1 de l'écran d'observation et vient exciter les couches de luminophores 28 produisant une émission lumineuse h1, visible à travers le verre support 22, et des électrons de rétrodiffusion Er1, Er2,.....Ern,. Ces électrons de rétrodiffusion, générés par les luminophores, sont renvoyés vers l'intérieur du tube et se trouvent absorbés partiellement, une première fois, en traversant la couche d'aluminium 30, dans leur déplacement vers l'intérieur du tube, puis se trouvent à nouveau absorbés partiellement, une seconde fois, en retombant sur l'écran d'observation, attirés par le potentiel de polarisation appliqué sur la couche d'aluminium. Au total avec une épaisseur d'aluminium de 2 micromètres environ et malgré la perte subie sur les électrons incidents Ei, traversant la couche d'aluminium 30, la réduction des électrons de rétrodiffusion absorbés par cette couche d'aluminium conduit à une amélioration notable du contraste de l'image.An incident electron beam Ei, crosses with a loss of electrons, the aluminum layer 30, in an area A1 of the screen of observation and excites the layers of phosphors 28 producing a light emission h1, visible through the support glass 22, and backscatter electrons Er1, Er2, ..... Ern ,. These backscatter electrons, generated by the phosphors, are returned to the inside of the tube and are found to be partially absorbed, a first time, by crossing the layer aluminum 30, in their displacement towards the inside of the tube, then find again partially absorbed a second time, falling back on the observation screen, attracted by the bias potential applied to the aluminum layer. In total with an aluminum thickness of 2 micrometers approximately and despite the loss suffered on the incident electrons Ei, passing through the aluminum layer 30, the reduction of the electrons backscatter absorbed by this aluminum layer leads to a noticeable improvement in image contrast.

Claims (4)

Tube intensificateur d'image radiologique comportant un tube électronique à vide et un écran d'observation luminescent (20), l'écran ayant un verre support (22) sur lequel est déposée une couche de luminophores, l'écran d'observation produisant une image lumineuse (h1) lorsque les luminophores sont excités par un faisceau d'électrons (Ei), et la couche de luminophores étant recouverte d'une couche d'aluminium, caractérisé en ce que la couche d'aluminium a une épaisseur d'au moins 1 micromètre dans le but de réduire d'une part la quantité d'électrons réémis de l'écran d'observation vers le tube et d'autre part la proportion de ces électrons qui reviennent frapper la couche de luminophores.X-ray image intensifier tube comprising a vacuum electronic tube and a luminescent observation screen (20), the screen having a support glass (22) on which a layer of phosphors, the observation screen producing a bright image (h1) when the phosphors are excited by an electron beam (Ei), and the layer of phosphors being covered with a layer of aluminum, characterized in that the aluminum layer has a thickness of at least 1 micrometer in order to reduce on the one hand the amount of re-emitted electrons from the observation screen towards the tube and on the other hand the proportion of these electrons returning to strike the phosphor layer. Tube intensificateur d'image radiologique selon la revendication 1, caractérisé en ce que l'épaisseur de la couche d'aluminium est comprise entre 1 et 3 micromètres environ.X-ray image intensifier tube according to claim 1, characterized in that the thickness of the aluminum layer is between 1 and 3 micrometers approximately. Tube intensificateur d'image radiologique selon la revendication 2, caractérisé en ce que la couche a une épaisseur d'environ 2 micromètres.X-ray image intensifier tube according to claim 2, characterized in that the layer has a thickness of approximately 2 micrometers. Tube intensificateur d'image radiologique selon l'une des revendications 1 à 3, caractérisé en ce que la couche est déposée directement sur les luminophores.X-ray image intensifier tube according to one claims 1 to 3, characterized in that the layer is deposited directly on the phosphors.
EP97403143A 1996-12-27 1997-12-23 Radiological image intensifier tube Expired - Lifetime EP0851455B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR9616114A FR2758002B1 (en) 1996-12-27 1996-12-27 VISUALIZATION SYSTEM WITH LUMINESCENT OBSERVATION SCREEN
FR9616114 1996-12-27

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EP0851455A1 true EP0851455A1 (en) 1998-07-01
EP0851455B1 EP0851455B1 (en) 2003-04-02

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US (1) US5981935A (en)
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JP (1) JPH10214573A (en)
DE (1) DE69720395T2 (en)
FR (1) FR2758002B1 (en)

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US7498557B2 (en) 2005-09-08 2009-03-03 Applied Materials Israel Ltd. Cascaded image intensifier
JP2007095631A (en) * 2005-09-30 2007-04-12 Toshiba Corp X-ray image tube
US7728274B2 (en) * 2007-03-30 2010-06-01 Subrahmanyam Pilla Imaging system with negative electron affinity photocathode

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DE2553507A1 (en) * 1975-11-28 1977-06-02 Licentia Gmbh Luminescent screen for image intensifier tubes - has metal foil on phosphor layer facing electron beam with heat reflecting properties
EP0067470A1 (en) * 1981-06-03 1982-12-22 Koninklijke Philips Electronics N.V. Display tube and method of manufacturing a display screen for such a display tube
DE4001516A1 (en) * 1990-01-19 1991-07-25 Siemens Ag Layer structure esp. for imaging screen - has transparent phosphor layer and polarisation on the sides of the layer structure
EP0610872A2 (en) * 1993-02-08 1994-08-17 Matsushita Electric Industrial Co., Ltd. Electron beam display device and production thereof
JPH0822784A (en) * 1994-05-02 1996-01-23 Matsushita Electric Ind Co Ltd Projecting cathode-ray tube and projection display device using the projecting cathode-ray tube

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Also Published As

Publication number Publication date
EP0851455B1 (en) 2003-04-02
FR2758002B1 (en) 2004-07-02
JPH10214573A (en) 1998-08-11
DE69720395D1 (en) 2003-05-08
FR2758002A1 (en) 1998-07-03
DE69720395T2 (en) 2004-03-25
US5981935A (en) 1999-11-09

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