EP0249547B1 - Method for making an x-ray image intensifier, and image intensifier so obtained - Google Patents

Method for making an x-ray image intensifier, and image intensifier so obtained Download PDF

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Publication number
EP0249547B1
EP0249547B1 EP87401281A EP87401281A EP0249547B1 EP 0249547 B1 EP0249547 B1 EP 0249547B1 EP 87401281 A EP87401281 A EP 87401281A EP 87401281 A EP87401281 A EP 87401281A EP 0249547 B1 EP0249547 B1 EP 0249547B1
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EP
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Prior art keywords
intensifier
photocathode
layer
anode
alkali metals
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EP87401281A
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German (de)
French (fr)
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EP0249547A2 (en
EP0249547A3 (en
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Gérard Vieux
Francis Diaz
Henri Rougeot
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Thales SA
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Thomson CSF SA
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J9/00—Apparatus or processes specially adapted for the manufacture, installation, removal, maintenance of electric discharge tubes, discharge lamps, or parts thereof; Recovery of material from discharge tubes or lamps
    • H01J9/02—Manufacture of electrodes or electrode systems
    • H01J9/12—Manufacture of electrodes or electrode systems of photo-emissive cathodes; of secondary-emission electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2201/00—Electrodes common to discharge tubes
    • H01J2201/32—Secondary emission electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2201/00—Electrodes common to discharge tubes
    • H01J2201/34—Photoemissive electrodes
    • H01J2201/342—Cathodes
    • H01J2201/3421—Composition of the emitting surface
    • H01J2201/3426—Alkaline metal compounds, e.g. Na-K-Sb

Definitions

  • the present invention relates to a method of manufacturing a radiological image intensifier. It also relates to the radiological image intensifiers thus obtained.
  • Radiological image intensifier tubes or I.I.R. are well known in the prior art. They transform a radiological image into a visible image, for example to ensure medical observation.
  • an IIR which is represented schematically, seen in longitudinal section in FIG. 1, consists of an input screen, an electronic optical system and an observation screen contained in a vacuum enclosure 1.
  • the input screen includes a scintillator 2 which converts the incident X photons into visible photons, a photocathode 3 which converts the visible photons into electrons. Between the scintillator and the photocathode, an electrically conductive sublayer is generally inserted, the role of which is to re-supply the photocathode with electrical charges while it emits its electrons. This sublayer is not shown in FIG. 1.
  • the scintillator may consist, for example, of cesium iodide doped with sodium or with thallium.
  • the photocathode can consist of an alkaline antimonide, of formula for example Sb Css, Sb K 3 , Sb K 2 Cs .
  • the conductive undercoat can consist, for example, of indium oxide of formula In 2 0 3 .
  • the electronic optical system generally consists of three electrodes G 1 , G 2 , G 3 and an anode A which carries the observation screen 4.
  • Photocathode 3 is generally connected to the ground of the tube.
  • the electrodes Gi, G 2 , G 3 and the anode A are brought to electrical potentials increasing up to 30 KV for example.
  • An electric field E is therefore created in the tube, directed along the longitudinal axis of the tube, towards the photocathode.
  • the electrons from the photocathode go up this field and strike the observation screen 4, made of a cathodoluminescent material such as zinc sulfide for example, which makes it possible to obtain a visible image.
  • the problem which arises and which the present invention seeks to solve is that one observes in the IIR, even in the absence of X-ray, a disturbing parasitic lighting of the observation screen.
  • This stray light is due to the alkali metals involuntarily deposited on the IIR electrodes during the development of the photocathode.
  • the intense electric field which reigns in the tube manages to tear electrons from these alkali metals which are very electro-positive, and therefore very easily ionizable. These electrons go up the electric field, strike the observation screen and create parasitic lighting.
  • FIG. 2 represents a partial section view of the grid G 3 and of the anode A of the IIR in FIG. 1.
  • the reference to the layer of alkali metals deposited on the grid is designated by reference 7 G 3 and which, under the action of the electric field E, prevailing between the grid G 3 and the anode A and directed towards the grid Ga, releases electrons which go up the electric field and strike the observation screen 4 .
  • photocathodes of the alkaline antimonide type are done in the vacuum chamber of the IR because the alkali metals are very reactive and must be created under vacuum to be stable.
  • These photocathodes can be produced by successive evaporations of their constituent elements.
  • an antimony generator which is constituted by a usual crucible containing antimony, which is caused to evaporate by heating the crucible, by Joule effect for example.
  • the antimony generator 5 is generally placed close to the photocathode and on the electron path as shown in FIG. 1, which explains why it is generally removed from the enclosure, once the photocathode is finished.
  • the alkali metals are evaporated from alkaline generators 6 generally located on the electrode G s , which is closest to the anode A, as shown in FIG. 1.
  • the alkaline generators are generally left in the vacuum enclosure once the photocathode is finished. There are known methods of manufacturing IR in which the alkaline generators are not carried by the electrode G 3 and are removed from the vacuum enclosure, once the photocathode is finished.
  • the evaporation of alkali metals is the result of silicothermia or aluminothermia of the chromates of the metals that we are trying to evaporate. Silicothermia or aluminothermia are triggered by Joule heating of alkaline generators.
  • Alkaline generators are much less directive than antimony generators. This is due to the fact that it is necessary for silicothermia or aluminothermia to occur under good conditions to use special crucibles in which the chromates are confined. This type of crucible has poor directivity which has the advantage of ensuring a very uniform deposition of alkali metals over the entire surface of the photocathode which is distant from these crucibles 6. It does, however, have the disadvantage of causing the deposition of alkali metals on all parts of the IIR tube, and in particular on the electrodes G 1 , G 2 and G 3 , which causes the problem of stray lighting of the observation screen.
  • This solution eliminates stray lighting from the observation screen, but introduces discharges through this oxide layer.
  • the IR When the IR receives X-rays, part of the electrons from the photocathode fall on the electrode Ga. As the electrode G 3 is covered with an oxide layer, these electrons do not flow and there occurs discharges through the oxide layer.
  • the present invention provides a solution to the problem mentioned which does not have the drawbacks of the known solution.
  • the present invention relates to a method of manufacturing an intensifier of radiological images, comprising in particular a photocathode consisting of an alkaline antimonide, several grids and an anode, characterized in that a layer of a conductive material of the electricity and having the property of oxidizing the alkali metals which enter into the composition of the photocathode is deposited at least on a part of the grid which is closest to the anode before introducing it into the intensifier.
  • a layer of an electrically conductive material is deposited on the grid G 3 on which the antimony generators are generally fixed. having the property of oxidizing alkali metals.
  • the problem of stray lighting is due to the metallic nature of the parasitic alkalies.
  • the solution proposed by the invention is to chemically react these alkali metals with a material capable of oxidizing them and transforming them into ionic or covalent compounds.
  • the alkali metals are fixed and no longer release electrons creating the stray light that we are trying to remove.
  • the deposit used must also be electrically conductive so as to avoid the discharge phenomena encountered in the prior art when an oxide layer covers the Ga electrode.
  • the invention proposes to use to cover the electrode G 3 of the IIR, before introducing it into the IIR, preferably, one of the following elements: selenium, tellurium, sulfur, arsenic, phosphorus, antimony ...
  • the electrode G 3 is covered with a layer 8, of tellurium for example, before being introduced into the IIR. It is possible to cover the whole of the electrode G 3 with tellurium or, as is the case in FIG. 3, only the zones of the electrode G 3 which are most likely to cause the phenomenon of parasitic lighting. These areas can be determined experimentally. They can also be determined by calculation using computer programs. The zones which are most likely to cause the phenomenon of parasitic lighting are generally very curved zones whose radius of curvature is small and whose electric field is strong. These areas are located near the alkaline generators and the observation screen. In FIG. 3, we see that the periphery of the orifice of the grid G 3 which allows the passage of the electrons has been covered with layer 8.
  • layer 8 which is sufficiently conductive, there is no problem of discharge.
  • this layer 8 there are also compounds of this layer and alkali metals, but whether these compounds are conductive or not, does not change the fact that layer 8 is sufficiently conductive so that there is no discharge and breakdown problem.
  • the layer 8 of electrically conductive material having the property of oxidizing the alkalis is deposited at least on the Ga electrode, which generally carries the alkaline generators and which is closest to the anode.
  • this layer 8 is also deposited on the grid G 2 .
  • this layer 8 it is also possible to cover with this layer 8 the grid G i , as well as more generally any part of the IR which must be electrically connected to an electrode of the IIR, that is to say say to one of the grids or to the anode.
  • One of these methods is to lay the neck che 8 by evaporation by heating by Joule effect a crucible containing the product to be deposited and causing condensation of the vapors from the crucible on the surfaces to be covered with layer 8.
  • Another method consists in dipping the parts to be covered with layer 8 in a reactive chemical bath which contains the product to be deposited.
  • Another process is electrolysis.
  • the part to be covered constitutes an electrode immersed in an electrolysis bath.
  • the deposition of layer 8 can also be carried out by sputtering or by using a plasma.

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Image-Pickup Tubes, Image-Amplification Tubes, And Storage Tubes (AREA)

Description

La présente invention concerne un procédé de fabrication d'un intensificateur d'images radiologiques. Elle concerne également les intensificateurs d'images radiologiques ainsi obtenus.The present invention relates to a method of manufacturing a radiological image intensifier. It also relates to the radiological image intensifiers thus obtained.

Les tubes intensificateurs d'images radiologiques ou I.I.R. sont bien connus de l'Art Antérieur. Ils transforment une image radiologique en image visible, par exemple pour assurer l'observation médicale.Radiological image intensifier tubes or I.I.R. are well known in the prior art. They transform a radiological image into a visible image, for example to ensure medical observation.

On rappelle qu'un IIR, qui est représenté de façon schématique, vu en coupe longitudinale sur la figure 1, est constitué par un écran d'entrée, un système d'optique électronique et un écran d'observation contenus dans une enceinte à vide 1.It will be recalled that an IIR, which is represented schematically, seen in longitudinal section in FIG. 1, consists of an input screen, an electronic optical system and an observation screen contained in a vacuum enclosure 1.

L'écran d'entrée comporte un scintillateur 2 qui convertit les photons X incidents en photons visibles, une photocathode 3 qui convertit les photons visibles en électrons. Entre le scintillateur et la photocathode, est généralement intercalée une sous-couche conductrice de l'électricité dont le rôle est de ré-approvisionner la photocathode en charges électriques pendant qu'elle émet ses électrons. Cette sous-couche n'est pas représentée sur la figure 1.The input screen includes a scintillator 2 which converts the incident X photons into visible photons, a photocathode 3 which converts the visible photons into electrons. Between the scintillator and the photocathode, an electrically conductive sublayer is generally inserted, the role of which is to re-supply the photocathode with electrical charges while it emits its electrons. This sublayer is not shown in FIG. 1.

Le scintillateur peut être constitué, par exemple, d'iodure de césium dopé au sodium ou au thallium. La photocathode peut être constituée d'un antimoniure alcalin, de formule par exemple Sb Css, Sb K3, Sb K2 Cs .....La sous-couche conductrice peut être constituée, par exemple, d'oxyde d'indium de formule In2 03.The scintillator may consist, for example, of cesium iodide doped with sodium or with thallium. The photocathode can consist of an alkaline antimonide, of formula for example Sb Css, Sb K 3 , Sb K 2 Cs ..... The conductive undercoat can consist, for example, of indium oxide of formula In 2 0 3 .

Le système d'optique électronique est constitué généralement de trois électrodes G1, G2, G3 et d'une anode A qui porte l'écran d'observation 4.The electronic optical system generally consists of three electrodes G 1 , G 2 , G 3 and an anode A which carries the observation screen 4.

La photocathode 3 est généralement reliée à la masse du tube. Les électrodes Gi, G2, G3 et l'anode A sont portées à des potentiels électriques croissant jusqu'à de 30 KV par exemple. Il se crée donc dans le tube un champ électrique E, dirigé selon l'axe longitudinal du tube, vers la photocathode. Les électrons issus de la photocathode remontent ce champ et viennent frapper l'écran d'observation 4, constitué d'un matériau cathodoluminescent tel que du sulfure de zinc par exemple, ce qui permet d'obtenir une image visible.Photocathode 3 is generally connected to the ground of the tube. The electrodes Gi, G 2 , G 3 and the anode A are brought to electrical potentials increasing up to 30 KV for example. An electric field E is therefore created in the tube, directed along the longitudinal axis of the tube, towards the photocathode. The electrons from the photocathode go up this field and strike the observation screen 4, made of a cathodoluminescent material such as zinc sulfide for example, which makes it possible to obtain a visible image.

Le problème qui se pose et que la présente invention cherche à résoudre est qu'on l'on observe dans les IIR, même en l'absence de rayonnement X, un éclairage parasite gênant de l'écran d'observation. Cet éclairage parasite est dû aux métaux alcalins déposés involontairement sur les électrodes de l'IIR lors de l'élaboration de la photocathode. Le champ électrique intense qui règne dans le tube parvient à arracher des électrons à ces métaux alcalins qui sont très électro-positifs, et donc très facilement ionisables. Ces électrons remontent le champ électrique, viennent percuter l'écran d'observation et créent un éclairage parasite.The problem which arises and which the present invention seeks to solve is that one observes in the IIR, even in the absence of X-ray, a disturbing parasitic lighting of the observation screen. This stray light is due to the alkali metals involuntarily deposited on the IIR electrodes during the development of the photocathode. The intense electric field which reigns in the tube manages to tear electrons from these alkali metals which are very electro-positive, and therefore very easily ionizable. These electrons go up the electric field, strike the observation screen and create parasitic lighting.

Ce phénomène est illustré sur la figure 2 qui représente une vue en coupe partielle de la grille G3 et de l'anode A de l'IIR de la figure 1. On désigne par la référence 7 la couche de métaux alcalins déposée sur la grille G3 et qui, sous l'action du champ électrique E, régnant entre la grille G3 et l'anode A et dirigé vers la grille Ga, libère des électrons qui remontent le champ électrique et viennent percuter l'écran d'observation 4.This phenomenon is illustrated in FIG. 2 which represents a partial section view of the grid G 3 and of the anode A of the IIR in FIG. 1. The reference to the layer of alkali metals deposited on the grid is designated by reference 7 G 3 and which, under the action of the electric field E, prevailing between the grid G 3 and the anode A and directed towards the grid Ga, releases electrons which go up the electric field and strike the observation screen 4 .

Il faut savoir que la fabrication des photocathodes du type antimoniure alcalin se fait dans l'enceinte à vide de l'lIR car les métaux alcalins sont très réactifs et doivent être créés sous vide pour être stables. Ces photocathodes peuvent être réalisées par évaporations successives de leurs éléments constitutifs. A cet effet, on dispose dans le tube, un générateur d'antimoine qui est constitué par un creuset usuel contenant de l'antimoine, dont on provoque l'évaporation en chauffant le creuset, par effet Joule par exemple. Le générateur d'antimoine 5 est généralement placé à proximité de la photocathode et sur le trajet des électrons comme cela est représenté sur la figure 1, ce qui explique qu'on l'enlève généralement de l'enceinte, une fois la photocathode terminée. Les métaux alcalins sont évaporés à partir de générateurs alcalins 6 situés généralement sur l'électrode Gs, qui est la plus proche de l'anode A, comme cela est représenté sur la figure 1.You should know that the manufacture of photocathodes of the alkaline antimonide type is done in the vacuum chamber of the IR because the alkali metals are very reactive and must be created under vacuum to be stable. These photocathodes can be produced by successive evaporations of their constituent elements. For this purpose, there is in the tube, an antimony generator which is constituted by a usual crucible containing antimony, which is caused to evaporate by heating the crucible, by Joule effect for example. The antimony generator 5 is generally placed close to the photocathode and on the electron path as shown in FIG. 1, which explains why it is generally removed from the enclosure, once the photocathode is finished. The alkali metals are evaporated from alkaline generators 6 generally located on the electrode G s , which is closest to the anode A, as shown in FIG. 1.

On laisse généralement les générateurs d'alcalins dans l'enceinte à vide une fois la photocathode terminé. On connait des procédés de fabrication d'lIR dans lesquels les générateurs d'alcalins ne sont pas portés par l'électrode G3 et sont enlevés de l'enceinte à vide, une fois la photocathode terminés.The alkaline generators are generally left in the vacuum enclosure once the photocathode is finished. There are known methods of manufacturing IR in which the alkaline generators are not carried by the electrode G 3 and are removed from the vacuum enclosure, once the photocathode is finished.

L'évaporation des métaux alcalins est le résultat d'une silicothermie ou d'une aluminothermie des chromates des métaux que l'on cherche à évaporer. La silicothermie ou l'aluminothermie sont déclenchées par le chauffage par effet Joule des générateurs alcalins.The evaporation of alkali metals is the result of silicothermia or aluminothermia of the chromates of the metals that we are trying to evaporate. Silicothermia or aluminothermia are triggered by Joule heating of alkaline generators.

Les générateur alcalins sont beaucoup moins directifs que les générateurs d'antimoine. Cela est dû au fait qu'il est nécessaire pour que la silicothermie ou l'aluminothermie se produisent dans de bonnes conditions d'utiliser des creusets particuliers dans lesquels les chromates sont confinés. Ce type de creuset présente une mauvaise directivité qui a l'avantage d'assurer un dépôt bien uniforme des métaux alcalins sur toute la surface de la photocathode qui est éloignée de ces creusets 6. Il a par contre l'inconvénient de provoquer le dépôt de métaux alcalins sur toutes les pièces du tube IIR, et notamment sur les électrodes G1, G2 et G3 ce qui entraîne le problème de l'éclairage parasite de l'écran d'observation.Alkaline generators are much less directive than antimony generators. This is due to the fact that it is necessary for silicothermia or aluminothermia to occur under good conditions to use special crucibles in which the chromates are confined. This type of crucible has poor directivity which has the advantage of ensuring a very uniform deposition of alkali metals over the entire surface of the photocathode which is distant from these crucibles 6. It does, however, have the disadvantage of causing the deposition of alkali metals on all parts of the IIR tube, and in particular on the electrodes G 1 , G 2 and G 3 , which causes the problem of stray lighting of the observation screen.

Pour résoudre ce problème, il est connu de recouvrir au moins une partie de l'électrode G3 d'une couche électriquement isolante de matériau organique, qui fixe les métaux alcalins (voir FR-A 2 176 850). Une autre solution utilisée par la Demanderesse est de recouvrir d'une couche d'oxyde l'électrode Ga, généralement en aluminium. Un tel procédé est décrit, par exemple, dans la demande de brevet français FR-A 2 168 553.To solve this problem, it is known to cover at least part of the electrode G 3 with an electrically insulating layer of organic material, which fixes the alkali metals (see FR-A 2 176 850). Another solution used by the Applicant is to cover the Ga electrode, generally of aluminum, with an oxide layer. Such a process is described, for example, in French patent application FR-A 2 168 553.

Cette solution permet de supprimer l'éclairage parasite de l'écran d'observation, mais introduit des décharges à travers cette couche d'oxyde.This solution eliminates stray lighting from the observation screen, but introduces discharges through this oxide layer.

Lorsque l'lIR reçoit un rayonnement X, une partie des électrons issus de la photocathode tombe sur l'électrode Ga. Comme l'électrode G3 est recouverte d'une couche d'oxyde, ces électrons ne s'écoulent pas et il se produit des décharges à travers la couche d'oxyde.When the IR receives X-rays, part of the electrons from the photocathode fall on the electrode Ga. As the electrode G 3 is covered with an oxide layer, these electrons do not flow and there occurs discharges through the oxide layer.

La présente invention propose une solution au problème évoqué qui ne présente pas les inconvénients de la solution connue.The present invention provides a solution to the problem mentioned which does not have the drawbacks of the known solution.

La présente invention a pour objet un procédé de fabrication d'un intensificateur d'images radiologiques, comportant notamment une photocathode constituée d'un antimoniure alcalin, plusieurs grilles et une anode, caractérisé en ce qu'une couche d'un matériau conducteur de l'électricité et ayant la propriété d'oxyder les métaux alcalins qui entrent dans la composition de la photocathode est déposée au moins sur une partie de la grille qui est la plus proche de l'anode avant de l'introduire dans l'intensificateur.The present invention relates to a method of manufacturing an intensifier of radiological images, comprising in particular a photocathode consisting of an alkaline antimonide, several grids and an anode, characterized in that a layer of a conductive material of the electricity and having the property of oxidizing the alkali metals which enter into the composition of the photocathode is deposited at least on a part of the grid which is closest to the anode before introducing it into the intensifier.

D'autres objets, caractéristiques et résultats de l'invention ressortiront de la description suivante, donnée à titre d'exemple non limitatif et illustrée par les figures annexées qui représentent :

  • - la figure 1, une vue en coupe longitudinale d'un IIR ;
  • - les figures 2 et 3, des vues en coupe de la grille G3 et de l'anode A de l'IIR de la figure 1 illustrant la solution connue selon l'Art Antérieur et la solution apportée par l'invention.
Other objects, characteristics and results of the invention will emerge from the following description, given by way of nonlimiting example and illustrated by the appended figures which represent:
  • - Figure 1, a longitudinal sectional view of an IIR;
  • - Figures 2 and 3, sectional views of the grid G 3 and the anode A of the IIR of Figure 1 illustrating the known solution according to the prior art and the solution provided by the invention.

Sur les différentes figures, les mêmes repères désignent les mêmes éléments, mais, pour des raisons de clarté, les cotes et proportions des divers éléments ne sont pas respectées.

  • Les figures 1 et 2 ont été décrites dans l'introduction à la description.
  • La figure 3 représente une vue en coupe partielle de la grille G3 et de l'anode A de l'IIR de la figure 1, illustrant la solution apportée par l'invention au problème de l'éclairage parasite précédemment évoqué.
In the various figures, the same references designate the same elements, but, for reasons of clarity, the dimensions and proportions of the various elements are not observed.
  • Figures 1 and 2 have been described in the introduction to the description.
  • FIG. 3 represents a view in partial section of the grid G 3 and of the anode A of the IIR of FIG. 1, illustrating the solution brought by the invention to the problem of the parasitic lighting previously mentioned.

Selon l'invention, avant de l'introduire dans l'enceinte à vide de l'IIR, on dépose sur la grille G3 sur laquelle sont généralement fixés les générateurs d'antimoine, une couche d'un matériau conducteur de l'électricité ayant la propriété d'oxyder les métaux alcalins.According to the invention, before introducing it into the IIR vacuum enclosure, a layer of an electrically conductive material is deposited on the grid G 3 on which the antimony generators are generally fixed. having the property of oxidizing alkali metals.

Le problème de l'éclairage parasite est dû à la nature métallique des alcalins parasitaires. La solution proposée par l'invention est de faire réagir chimiquement ces métaux alcalins avec un matériau capable de les oxyder et de les transformer en composés ioniques ou covalents. Ainsi les métaux alcalins sont fixés et ne libèrent plus d'électrons créant l'éclairage parasite que l'on cherche à supprimer. Le dépôt utilisé doit être de plus conducteur de l'électricité de façon à éviter les phénomènes de décharge rencontrés dans l'Art Antérieur lorsqu'une couche d'oxyde recouvre l'électrode Ga.The problem of stray lighting is due to the metallic nature of the parasitic alkalies. The solution proposed by the invention is to chemically react these alkali metals with a material capable of oxidizing them and transforming them into ionic or covalent compounds. Thus the alkali metals are fixed and no longer release electrons creating the stray light that we are trying to remove. The deposit used must also be electrically conductive so as to avoid the discharge phenomena encountered in the prior art when an oxide layer covers the Ga electrode.

L'invention propose d'utiliser pour recouvrir l'électrode G3 de l'IIR, avant de l'introduire dans l'IIR, de préférence, l'un des éléments suivants :sélénium, tellure, soufre, arsenic, phosphore, antimoine...The invention proposes to use to cover the electrode G 3 of the IIR, before introducing it into the IIR, preferably, one of the following elements: selenium, tellurium, sulfur, arsenic, phosphorus, antimony ...

On peut utiliser ces éléments seuls ou sous forme de composés ayant par exemple l'une des formules suivantes : Pb Te, Cd Te, Zn Te, In Te, Pb Se, Cd Se, Zn Se, In Se, Pb S, Cd S, Zn S, Zn3 P2...These elements can be used alone or in the form of compounds having for example one of the following formulas: Pb Te, Cd Te, Zn Te, In Te, Pb Se, Cd Se, Zn Se, In Se, Pb S, Cd S , Zn S, Zn 3 P 2 ...

Sur la figure 3 on montre que l'électrode G3 est recouverte d'une couche 8, de tellure par exemple, avant d'être introduite dans l'IIR. On peut recouvrir la totalité de l'électrode G3 de tellure ou, comme c'est le cas sur la figure 3, uniquement les zones de l'électrode G3 qui sont les plus susceptibles de provoquer le phénomène d'éclairage parasite. Ces zones peuvent être déterminées expérimentalement. Elles peuvent aussi être déterminées par le calcul en utilisant des programmes d'ordinateurs. Les zones qui sont les plus susceptibles de provoquer le phénomène d'éclairage parasite sont généralement des zones très courbées dont le rayon de courbure est faible et dont le champ électrique est fort. Ces zones sont situées à proximité des générateurs d'alcalins et de l'écran d'observation. Sur la figure 3, on voit qu'on a recouvert de la couche 8 la périphérie de l'orifice de la grille G3 qui permet le passage des électrons.In FIG. 3 it is shown that the electrode G 3 is covered with a layer 8, of tellurium for example, before being introduced into the IIR. It is possible to cover the whole of the electrode G 3 with tellurium or, as is the case in FIG. 3, only the zones of the electrode G 3 which are most likely to cause the phenomenon of parasitic lighting. These areas can be determined experimentally. They can also be determined by calculation using computer programs. The zones which are most likely to cause the phenomenon of parasitic lighting are generally very curved zones whose radius of curvature is small and whose electric field is strong. These areas are located near the alkaline generators and the observation screen. In FIG. 3, we see that the periphery of the orifice of the grid G 3 which allows the passage of the electrons has been covered with layer 8.

L'arrivée d'alcalins parasitaires lors de la fabrication de la photocathode provoque la réaction suivante à la surface de la couche 8 de tellure dans le cas où du césium est évaporé :

  • 2Cs+Te → Cs2Te
The arrival of parasitic alkalis during the manufacture of the photocathode causes the following reaction on the surface of the tellurium layer 8 in the case where cesium is evaporated:
  • 2Cs + Te → Cs 2 Te

On ne retrouve donc pas sur la couche 8 de métaux alcalins mais des composés comportant ces alcalins.We therefore do not find on layer 8 alkali metals but compounds comprising these alkalis.

Du fait de ces composés, tel celui de formule Cs2 Te, malgré le champ électrique existant entre la grille G3 et la cathode, on n'observe plus d'émission d'électrons provoquant un éclairage parasite de l'écran d'observation.Because of these compounds, such as that of formula Cs 2 Te, in spite of the electric field existing between the grid G 3 and the cathode, no more emission of electrons is observed causing parasitic lighting of the observation screen .

De plus, du fait de la présence de la couche 8, qui est suffisament conductrice, il n'y a pas de problème de décharge. Dans cette couche 8, il y a aussi des composés de cette couche et des métaux alcalins, mais que ces composés soient conducteurs ou non, ne change pas le fait que la couche 8 soit suffisamment conductrice pour qu'il n'y ait pas de problème de décharge et de claquage.In addition, due to the presence of layer 8, which is sufficiently conductive, there is no problem of discharge. In this layer 8, there are also compounds of this layer and alkali metals, but whether these compounds are conductive or not, does not change the fact that layer 8 is sufficiently conductive so that there is no discharge and breakdown problem.

A titre d'exemple, lorsqu'on évapore du césium et que la couche 8 est en tellure de plomb, la réaction est la suivante :

  • 2Cs + Pb Te → Cs2 Te + < <Pb> >p b Te
As an example, when cesium is evaporated and layer 8 is made of lead tellurium, the reaction is as follows:
  • 2Cs + Pb Te → Cs 2 Te + <<Pb>> p b T e

Il y a donc génération de plomb qui reste dissout dans la couche 8 en tellure de plomb.There is therefore generation of lead which remains dissolved in layer 8 of lead tellurium.

On dépose la couche 8 de matériau conducteur de l'électricité et ayant la propriété d'oxyder les alcalins au moins sur l'électrode Ga, qui porte généralement les générateurs alcalins et, qui est la plus proche de l'anode.The layer 8 of electrically conductive material having the property of oxidizing the alkalis is deposited at least on the Ga electrode, which generally carries the alkaline generators and which is closest to the anode.

Pour supprimer plus complètement l'éclairement parasite de l'écran d'observation, on dépose aussi cette couche 8 sur la grille G2.To more completely remove the stray light from the observation screen, this layer 8 is also deposited on the grid G 2 .

On peut par mesure de précaution recouvrir également de cette couche 8 la grille Gi, ainsi que d'une façon plus générale toute pièce de l'lIR qui doit être reliée électriquement à une électrode de l'IIR, c'est-à-dire à l'une des grilles ou à l'anode.As a precaution, it is also possible to cover with this layer 8 the grid G i , as well as more generally any part of the IR which must be electrically connected to an electrode of the IIR, that is to say say to one of the grids or to the anode.

Pour déposer la couche 8, divers procédés sont utilisables.To deposit layer 8, various methods can be used.

L'un de ces procédés consiste à déposer la couche 8 par évaporation en chauffant par effet Joule un creuset contenant le produit à déposer et en provoquant la condensation des vapeurs issues du creuset sur les surfaces à recouvrir de la couche 8.One of these methods is to lay the neck che 8 by evaporation by heating by Joule effect a crucible containing the product to be deposited and causing condensation of the vapors from the crucible on the surfaces to be covered with layer 8.

Un autre procédé consiste à tremper les pièces à recouvrir de la couche 8 dans un bain chimique réactif qui comporte le produit à déposer.Another method consists in dipping the parts to be covered with layer 8 in a reactive chemical bath which contains the product to be deposited.

Un autre procédé est l'électrolyse. Dans ce cas la pièce à recouvrir constitue une électrode plongeant dans un bain d'électrolyse.Another process is electrolysis. In this case, the part to be covered constitutes an electrode immersed in an electrolysis bath.

Le dépôt de la couche 8 peut être aussi réalisé par pulvérisation cathodique ou en utilisant un plasma.The deposition of layer 8 can also be carried out by sputtering or by using a plasma.

Tous les procédés qui viennent d'être évoqués pour déposer la couche 8 sont bien connus et leur liste n'est pas limitative.All the processes which have just been mentioned for depositing layer 8 are well known and their list is not exhaustive.

Comme cela a été expliqué précédemment, on peut sans inconvénient déposer la couche 8 sur la totalité des grilles Gi, G2, G3 et des pièces reliées électriquement à une électrode de l'IIR ou seulement sur une partie de ces grilles et de ces pièces.As has been explained previously, it is possible without deposit to deposit the layer 8 on all of the gates Gi, G 2 , G 3 and of the parts electrically connected to an electrode of the IIR or only on a part of these grids and of these rooms.

Claims (12)

1. A method for the manufacture of a radiological image intensifier, comprising more especially a photocathode (3) made up of an alkali metal antimonide, several grids (G1, G2 and Gs) and an anode (A), characterized in that a layer (a) of an electrically conducting material and having the property of oxidizing the alkali metals which enter into the composition of the photocathode (3) is disposed at least on a part of the grid (Ga) which is nearest to the anode (A) before its introduction into the intensifier.
2. The method as claimed in claim 1, characterized in that a layer (8) of an electrically conducting material having the property of oxidizing the alkali metals which enter into the composition of the photocathode is disposed at least on a part of the grid (G2) near that grid (Ga) which is nearest to the anode (A) before introducing it into the intensifier.
3. The method as claimed in claim 1 or claim 2, characterized in that a layer of an electrically conducting material with the property of oxidizing the alkali metals entering into the composition of the photocathode is placed at least on a part of the other grids (G1 and G2) of the intensifier before their introduction into the intensifier.
4. The method as claimed in claim 3, characterized in that a layer of an electrically conducting material having the property of oxidizing the alkali metals which enter into the composition of the photocathode is disposed at least on part of all the members of the intensifier which are to be connected electrically with one of the grids or with the anode of the intensifier before introducing them into the intensifier.
5. The method as claimed in any one of the claims 1 through 4, characterized in that the deposition of the said layer (8) is performed in accordance with one of the following techniques: deposition by condensation - deposition by dipping in a chemical bath - deposition by electrolysis - deposition by cathodic sputtering plasma coating.
6. A radiological image intensifier comprising more especially a photocathode (3), made up of an alkali metal antimonide, several grids (Gi, G2 and Ga) and an anode (A), characterized in that at least a part of the grid (Ga) which is nearest to the anode (A) carries a layer (8) of an electrically conducting material having the property of oxidizing the alkali metals which enter into the composition of the photocathode (3).
7. The intensifier as claimed in claim 6, characterized in that at least a part of the grid (G2) near to that grid (Ga) which is nearest to the anode (A) carries a layer (8) of an electrically conducting material having the property of oxidizing the alkali metals which enter into the composition of the photocathode (3).
8. The intensifier as claimed in claim 6 or claim 7, characterized in that the other grids of the intensifier carry on at least a part thereof a layer (8) of an electrically conducting material having the property of oxidizing the alkali metals which enter into the composition of the photocathode (3).
9. The intensifier as a claimed in claim 8, characterized in that the members of the intensifier which are electrically connected with one of the grids or with the anode of the intensifier carry at least on a part thereof a layer (8) of an electrically conducting material having the property of oxidizing the alkali metals which enter into the composition of the photocathode.
10. The intensifier as claimed in any one of the claims 6 through 9, characterized in that the said material is one of the following elements: selenium tellurium, sulfur, arsenic, phosphorus and antimony.
11. The intensifier as claimed in any one of the claims 6 through 9, characterized in that the said material is a compound comprising one of the following elements: selenium, tellurium, sulfur, arsenic, phosphorus and antimony.
12. The intensifier as claimed in claim 11, characterized in that the compound is one of the following ones: PbTe, CDTe, ZnTe, InTe, PbSe, CdSe, ZNSe, InSe, PbS, CdS, ZnS and Zn3P2.
EP87401281A 1986-06-13 1987-06-05 Method for making an x-ray image intensifier, and image intensifier so obtained Expired - Lifetime EP0249547B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8608588A FR2600177B1 (en) 1986-06-13 1986-06-13 METHOD FOR MANUFACTURING A RADIOLOGICAL IMAGE INTENSIFIER AND RADIOLOGICAL IMAGE INTENSIFIER THUS OBTAINED
FR8608588 1986-06-13

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EP0249547A2 EP0249547A2 (en) 1987-12-16
EP0249547A3 EP0249547A3 (en) 1988-01-13
EP0249547B1 true EP0249547B1 (en) 1990-01-10

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EP (1) EP0249547B1 (en)
JP (1) JPH0821335B2 (en)
DE (1) DE3761405D1 (en)
FR (1) FR2600177B1 (en)

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JPS5958920A (en) * 1982-09-28 1984-04-04 Fujitsu Ltd Buffer circuit
FR2634057B1 (en) * 1988-07-08 1991-04-19 Thomson Csf PROCESS FOR THE MANUFACTURE OF AN IMPROVED TUBE INTENSIFYING RADIOLOGICAL IMAGES, INTENSIFYING TUBE THUS OBTAINED
FR2650438B1 (en) * 1989-07-28 1996-07-05 Thomson Tubes Electroniques METHOD FOR MANUFACTURING IMPROVED IMAGE INTENSIFIER TUBE, INTENSIFIER TUBE THUS OBTAINED
US5306907A (en) * 1991-07-11 1994-04-26 The University Of Connecticut X-ray and gamma ray electron beam imaging tube having a sensor-target layer composed of a lead mixture
FR2700889B1 (en) † 1993-01-22 1995-02-24 Thomson Tubes Electroniques Image converter tube, and method for suppressing stray light in this tube.
FR2782388B1 (en) 1998-08-11 2000-11-03 Trixell Sas SOLID STATE RADIATION DETECTOR WITH INCREASED LIFE

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FR1585625A (en) * 1968-07-02 1970-01-30 Thomson Csf
FR2119203A5 (en) * 1970-12-23 1972-08-04 Thomson Csf
IL41312A (en) * 1972-01-21 1975-06-25 Varian Associates Image tube employing high field electron emission suppression
DE2213493C3 (en) * 1972-03-20 1980-02-28 Siemens Ag, 1000 Berlin Und 8000 Muenchen Electronic image intensifier tube in which an electrically conductive TeU is provided with an electrically insulating layer, and method for producing this layer
US4069121A (en) * 1975-06-27 1978-01-17 Thomson-Csf Method for producing microscopic passages in a semiconductor body for electron-multiplication applications
FR2335056A1 (en) * 1975-09-12 1977-07-08 Thomson Csf DEVICE FOR DISPLAYING INFORMATION GIVEN IN THE FORM OF RADIATED ENERGY
FR2345815A1 (en) * 1976-01-30 1977-10-21 Thomson Csf NEW SOLID IONIZING RADIATION DETECTOR
FR2344132A1 (en) * 1976-03-09 1977-10-07 Thomson Csf SEMICONDUCTOR IONIZING RADIATION DETECTOR
FR2351422A1 (en) * 1976-05-14 1977-12-09 Thomson Csf DETECTOR DEVICE, SOLID LOCATOR OF IONIZING RADIATION IMPACTS
FR2352346A1 (en) * 1976-05-18 1977-12-16 Thomson Csf NEW SCINTIGRAPHY SHOOTING SET
FR2361790A1 (en) * 1976-08-10 1978-03-10 Thomson Csf DEVICE WITH SEMICONDUCTOR ELEMENTS FOR THE DISPLAY OF AN ELECTRIC SIGNAL
FR2502842A1 (en) * 1981-03-27 1982-10-01 Thomson Csf IMAGE INTENSIFIER TUBE TARGET AND VIDEO OUTPUT INTENSIFICATION TUBE PROVIDED WITH SUCH TARGET
US4475059A (en) * 1982-06-01 1984-10-02 International Telephone And Telegraph Corporation Image intensifier tube with reduced veiling glare and method of making same
JPS6056341A (en) * 1983-09-06 1985-04-01 Hamamatsu Photonics Kk Image tube and manufacture of the same

Also Published As

Publication number Publication date
EP0249547A2 (en) 1987-12-16
FR2600177A1 (en) 1987-12-18
JPS63935A (en) 1988-01-05
US4862006A (en) 1989-08-29
EP0249547A3 (en) 1988-01-13
JPH0821335B2 (en) 1996-03-04
FR2600177B1 (en) 1988-08-19
DE3761405D1 (en) 1990-02-15

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