EP0215699A1 - Scintillator input screen for an X-ray image intensifier, and method of manufacturing such a scintillator - Google Patents

Scintillator input screen for an X-ray image intensifier, and method of manufacturing such a scintillator Download PDF

Info

Publication number
EP0215699A1
EP0215699A1 EP86401835A EP86401835A EP0215699A1 EP 0215699 A1 EP0215699 A1 EP 0215699A1 EP 86401835 A EP86401835 A EP 86401835A EP 86401835 A EP86401835 A EP 86401835A EP 0215699 A1 EP0215699 A1 EP 0215699A1
Authority
EP
European Patent Office
Prior art keywords
needles
scintillator
cesium iodide
manufacturing
coating material
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP86401835A
Other languages
German (de)
French (fr)
Other versions
EP0215699B1 (en
Inventor
Henri Rougeot
Gérard Vieux
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Thales SA
Original Assignee
Thomson CSF SA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Thomson CSF SA filed Critical Thomson CSF SA
Publication of EP0215699A1 publication Critical patent/EP0215699A1/en
Application granted granted Critical
Publication of EP0215699B1 publication Critical patent/EP0215699B1/en
Expired legal-status Critical Current

Links

Images

Classifications

    • 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
    • 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
    • H01J29/36—Photoelectric screens; Charge-storage screens
    • H01J29/38—Photoelectric screens; Charge-storage screens not using charge storage, e.g. photo-emissive screen, extended cathode
    • H01J29/385—Photocathodes comprising a layer which modified the wave length of impinging radiation

Definitions

  • the present invention relates to an input screen scintillator for an X-ray image intensifier tube. It also relates to a method of manufacturing such a scintillator.
  • Radiological image intensifier tubes are well known in the prior art. They make it possible to transform a radiological image into a visible image, generally to ensure medical observation.
  • These tubes consist of an input screen, an electronic optical system and an observation screen.
  • the input screen has a scintillator which converts the incident X photons into visible photons. These visible photons then strike a photocathode, generally constituted by an alkaline antimonide, which, thus excited, generates a flow of electrons.
  • the photocathode is not deposited directly on the scintillator but on an electrically conductive sublayer which makes it possible to reconstitute the charges of the photocathode material.
  • This sub-layer can for example consist of alumina, indium oxide or a mixture of these two bodies.
  • the flow of electrons from the photocathode is then transmitted by the electronic optical system which focuses the electrons and directs them on an observation screen made up of a luminograph which then emits visible light.
  • This light can then be processed, for example, by a television, cinema or photography system.
  • the scintillator of the entry screen generally consists of cesium iodide deposited by evaporation under vacuum on a substrate. Evaporation can take place on a cold or hot substrate.
  • the substrate generally consists of an aluminum cap with a spherical or hyperbolic profile. A thickness of cesium iodide is deposited which is generally between 150 and 500 microns.
  • Cesium iodide is naturally deposited in the form of needles 5 to 10 micrometers in diameter. Its refractive index being 1.8, there is a certain optical fiber effect which minimizes the lateral scattering of the light generated within the material.
  • FIG 1 there is shown schematically an aluminum substrate 1 carrying a few needles 2 of cesium iodide.
  • the aluminum substrate receives a flow of X photons symbolized by vertical arrows.
  • the normal paths which bear the reference 3. cause the production of a light signal at l 'end of cesium iodide needles, There is also laterally scattered light carried by cesium iodide needles. as indicated in the figure by reference 4.
  • the resolution of the tube depends on the ability of the cesium iodide needles to properly channel the light. It depends on the thickness of the cesium iodide layer. An increase in thickness leads to a deterioration in resolution. But, moreover, the greater the thickness of cesium iodide, the more the X-rays are absorbed. A compromise must therefore be found between the absorption of X-rays and the resolution.
  • This heat treatment takes place immediately after the evaporation of the cesium iodide under vacuum. It ensures the luminescence of the screen due to the doping of cesium iodide by sodium or thallium ions for example.
  • This heat treatment generally consists in bringing the screen to the temperature of approximately 340 ° C., for approximately one hour, by placing it in an atmosphere of dry air or nitrogen.
  • the present invention proposes to solve the problem posed by the heat treatment in the following manner.
  • the cesium iodide needles of the scintillator are coated with a refractory material, transparent or reflective, and with an optical index close to or less than that of cesium iodide. Due to this coating, the needles are not coalesced during the heat treatment subsequent to the coating, which ensures the luminescence of the screen.
  • the invention also relates to methods of manufacturing such a scintillator.
  • FIG. 3 schematically represents a screen scintillator of an X-ray image intensifier tube according to the invention.
  • a substrate 1 made of aluminum for example, carrying a few needles of cesium iodide.
  • needles 2 are coated with a refractory material 5, transparent and with an optical index close to or less than that of cesium iodide.
  • the needles are therefore coated with a material which is inserted into the interstices between the needles and which acts as a mechanical barrier by keeping the needles isolated from each other during the subsequent heat treatment, intended to ensure the luminescence of the screen.
  • This material must be refractory, that is to say have a melting point as high as possible so as not to be affected by the heat treatment. It must be transparent or reflective so as not to absorb light. Finally, this material must have an optical index close to or lower than that of cesium iodide so as to maintain an effect of optical fibers.
  • the coating material 5 may be an oxide of a metal or of a non-metal, a polymerizable resin of the silicone type, an organometallic compound, etc.
  • curves 6 and 7 show, as a function of the spatial frequency, in pairs of lines per centimeter that the modulation transfer function (FTM), in percentage, is higher in the case of the scintillator according to the invention, curve 7, than in the case of a scintillator according to the prior art, curve 6.
  • the invention therefore makes it possible to obtain a high resolution and an FTM high.
  • C.V.D. chemical vapor deposition
  • This method is commonly used in the field of semiconductors for depositing a thin film material on a flat substrate. According to the invention, this method is used to deposit a material in a thin layer on an essentially vertical substrate constituted by each needle of the scintillator. It should be emphasized that the difficulty in achieving the coating of the needles arises from the fact that the interstices between needles have a great length with respect to their diameter, their length being approximately a thousand times greater than their diameter.
  • the coating material deposited by this process can be any oxide of a metal or of a non-metal which is refractory, transparent - or reflective, and with an optical index close to or less than that of cesium iodide.
  • the coating material used can have one of the following formulas: Si 0, Si 0 2 , Si O x with 1 ⁇ x ⁇ 2, AI 2 O 3 , Sb 2 O 5 ...
  • the activation of the CVD process can be carried out by thermal excitation: this is the high temperature CVD. It includes initial vacuuming, followed by atmospheric pressure. Reactive vapor deposition is carried out using a mixture of gases such as silane Si H 4 . oxygen, and nitrogen oxide N 2 O. The molecules of the mixture recombine to form silica Si 0 2 which is deposited on the needles of cesium iodide. It is also possible to deposit silicon nitride Si 3 N 4 by the same type of process.
  • the high temperature CVD requires using a temperature above 300 "C.
  • the activation of the CVD process can also be carried out by plasma excitation, around 100 "C, or by photonic excitation, around 100 ° C. Also.
  • the coating layer can be silicon nitride If 3 N 4.
  • Activation of the CVD process can also be achieved by the use of a lower pressure high temperature process (LPCVD technique).
  • Another method for producing the screen according to the invention can be the coating by diffusion of a colloidal solution inside the interstices between needles.
  • a colloidal solution of Si 0 2 , or of AI 2 0 3 , Sb 2 Os can be used. Sn 0 4 , for example.
  • the diffusion coating is followed by a heat treatment which causes the deposition of the coating material, for example Si 0 2 in the case of a colloidal solution of Si 0 2 .
  • This heat treatment can be carried out at the same time as the heat treatment intended to cause the luminescence of the cesium iodide needles.
  • Another process for producing the screen according to the invention is the vacuum coating with a polymer resin of the silicone type or any polyimide material. Curing of the coating material occurs either at room temperature. either hot.
  • a final method consists in carrying out the coating by diffusion of an organo-metallic compound in the interstices between the needles.
  • organo-metallic compound An example of such a compound that may be mentioned is tetramethoxy-silane, tetra-ethoxy-silane or silicon tetra-acetate. This organometallic compound must undergo treatment at high temperature or hydrolysis in air.

Abstract

La présente invention concerne un scintillateur d'écran d'entrée de tube intensificateur d'images radiologiques dont, les aiguilles (2) en iodure de césium du scintillateur sont enrobées par un matériau (5) réfractaire, transparent ou réfléchissant et d'indice optique voisin ou inférieur à celui de l'iodure de césium. Divers procédés peuvent être utilisés pour l'enrobage, tels que le dépôt chimique en phase vapeur, activé par excitation thermique, excitation plasma, ou excitation photonique : ou tels que le dépôt par diffusion d'une solution colloïdale ; ou tels que la polymérisation d'une résine polymère. Après l'enrobage. on réalise le traitement thermique qui assure la luminescence de l'écran.

Figure imgaf001
The present invention relates to a scintillator for an input screen for a tube for intensifying radiological images, the cesium iodide needles (2) of the scintillator of which are coated with a refractory, transparent or reflecting material (5) close to or less than that of cesium iodide. Various methods can be used for coating, such as chemical vapor deposition, activated by thermal excitation, plasma excitation, or photonic excitation: or such as the diffusion deposit of a colloidal solution; or such as the polymerization of a polymer resin. After coating. the heat treatment is carried out which ensures the luminescence of the screen.
Figure imgaf001

Description

La présente invention concerne un scintillateur d'écran d'entrée de tube intensificateur d'images radiologiques. Elle concerne également un procédé de fabrication d'un tel scintillateur.The present invention relates to an input screen scintillator for an X-ray image intensifier tube. It also relates to a method of manufacturing such a scintillator.

Les tubes intensificateurs d'images radiologiques sont bien connus de l'art antérieur. Ils permettent de transformer une image radiologique en image visible, généralement pour assurer l'observation médicale.Radiological image intensifier tubes are well known in the prior art. They make it possible to transform a radiological image into a visible image, generally to ensure medical observation.

Ces tubes sont constitués par un écran d'entrée, un système d'optique électronique et un écran d'observation.These tubes consist of an input screen, an electronic optical system and an observation screen.

L'écran d'entrée comporte un scintillateur qui convertit les photons X incidents en photons visibles. Ces photons visibles viennent ensuite frapper une photocathode, généralement constituée par un antimoniure alcalin, qui, ainsi excité, génère un flux d'électrons. La photocathode n'est pas déposée directement sur le scintillateur mais sur une sous-couche conductrice de l'électricité qui permet de reconstituer les charges du matériau de la photocathode. Cette sous-couche peut par exemple être constituée d'alumine, d'oxyde d'indium ou d'un mélange de ces deux corps.The input screen has a scintillator which converts the incident X photons into visible photons. These visible photons then strike a photocathode, generally constituted by an alkaline antimonide, which, thus excited, generates a flow of electrons. The photocathode is not deposited directly on the scintillator but on an electrically conductive sublayer which makes it possible to reconstitute the charges of the photocathode material. This sub-layer can for example consist of alumina, indium oxide or a mixture of these two bodies.

Le flux d'électrons issu de la photocathode est ensuite transmis par le système d'optique électronique qui focalise les électrons et les dirige sur un écran d'observation constitué d'un luminographe qui émet alors une lumière visible. Cette lumière peut ensuite être traitée, par exemple, par un système de télévision, de cinéma ou de photographie.The flow of electrons from the photocathode is then transmitted by the electronic optical system which focuses the electrons and directs them on an observation screen made up of a luminograph which then emits visible light. This light can then be processed, for example, by a television, cinema or photography system.

Le scintillateur de l'écran d'entrée est généralement constitué d'iodure de césium déposé par évaporation sous vide sur un substrat. L'évaporation peut avoir lieu sur un substrat froid ou chaud. Le substrat est généralement constitué par une calotte d'aluminium à profil sphérique ou hyperbolique. On dépose une épaisseur d'iodure de césium qui est généralement comprise entre 150 et 500 micro mètres.The scintillator of the entry screen generally consists of cesium iodide deposited by evaporation under vacuum on a substrate. Evaporation can take place on a cold or hot substrate. The substrate generally consists of an aluminum cap with a spherical or hyperbolic profile. A thickness of cesium iodide is deposited which is generally between 150 and 500 microns.

L'iodure de césium se dépose naturellement sous forme d'aiguilles de 5 à 10 micromètres de diamètre. Son indice de réfraction étant de 1,8, on bénéficie d'un certain effet de fibre optique qui minimise la diffusion latérale de la lumière générée au sein du matériau.Cesium iodide is naturally deposited in the form of needles 5 to 10 micrometers in diameter. Its refractive index being 1.8, there is a certain optical fiber effect which minimizes the lateral scattering of the light generated within the material.

Sur la figure 1, on a représenté de façon schématique un substrat en aluminium 1 portant quelques aiguilles 2 en iodure de césium. Le substrat en aluminium reçoit un flux de photons X symbolisés par des flèches verticales. On a représenté en pointillés sur la figure des exemples de trajets suivis dans les aiguilles d'iodure de césium par le rayonnement visible correspondant aux photons X incidents Les trajets normaux, qui portent la référence 3. entraînent la production d'un signal lumineux à l'extrémité des aiguilles en iodure de césium, Il y a également diffusion latéralement de la lumière véhiculée par les aiguilles d'iodure de césium. comme cela est indiqué sur la figure par la référence 4.In Figure 1, there is shown schematically an aluminum substrate 1 carrying a few needles 2 of cesium iodide. The aluminum substrate receives a flow of X photons symbolized by vertical arrows. There are shown in dotted lines in the figure examples of paths followed in cesium iodide needles by the visible radiation corresponding to the incident X photons. The normal paths, which bear the reference 3. cause the production of a light signal at l 'end of cesium iodide needles, There is also laterally scattered light carried by cesium iodide needles. as indicated in the figure by reference 4.

La résolution du tube dépend de la capacité des aiguilles d'iodure de césium à bien canaliser la lumière. Elle dépend de l'épaisseur de la couche d'iodure de césium. Une augmentation d'épaisseur entraîne une détérioration de la résolution. Mais, par ailleurs, plus l'épaisseur d'iodure de césium est importante, plus les rayons X sont absorbés. Il faut donc trouver un compromis entre l'absorption des rayons X et la résolution.The resolution of the tube depends on the ability of the cesium iodide needles to properly channel the light. It depends on the thickness of the cesium iodide layer. An increase in thickness leads to a deterioration in resolution. But, moreover, the greater the thickness of cesium iodide, the more the X-rays are absorbed. A compromise must therefore be found between the absorption of X-rays and the resolution.

Un autre facteur qui joue sur la résolution du tube est le traitement thermique que doit subir l'écran d'entrée lors de sa fabrication. Ce traitement a lieu immédiatement après l'évaporation sous vide de l'iodure de césium. Il assure la luminescence de l'écran du fait du dopage de l'iodure de césium par des ions de sodium ou de thallium par exemple. Ce traitement thermique consiste généralement à porter l'écran à la température d'environ 340°C, pendant une heure environ, en le plaçant dans une atmosphère d'air sec ou d'azote.Another factor that plays on the resolution of the tube is the heat treatment that the input screen must undergo during its manufacture. This treatment takes place immediately after the evaporation of the cesium iodide under vacuum. It ensures the luminescence of the screen due to the doping of cesium iodide by sodium or thallium ions for example. This heat treatment generally consists in bringing the screen to the temperature of approximately 340 ° C., for approximately one hour, by placing it in an atmosphere of dry air or nitrogen.

Le problème qui se pose est, qu'au cours de ce traitement thermique absolument obligatoire, les aiguilles du scintillateur subissent une certaine coalescence et s'agglomèrent entre elles, comme cela a été représenté schématiquement sur la figure 2. Cette coalescence entraîne une diffusion latérale de la lumière plus importante, voir les flèches en pointillés portant le repère 4, et la résolution se trouve détériorée.The problem which arises is, that during this absolutely compulsory heat treatment, the needles of the scintillator undergo a certain coalescence and agglomerate between them, as has been represented diagrammatically in FIG. 2. This coalescence causes a lateral diffusion more important light, see the dotted arrows marked 4, and the resolution is deteriorated.

Pour supprimer la coalescence qui se produit lors du traitement thermique, on a proposé, dans l'art antérieur, de réaliser le scintillateur de l'écran d'entrée en évaporant alternativement de l'iodure de césium pur et de l'iodure de césium dopé avec un matériau réfractaire. On espérait que des aiguilles ainsi constituées par des couches alternées d'iodure de césium pur et d'iodure de césium dopé avec un matériau réfractaire n'entreraient pas en contact lors du traitement thermique. Cette solution n'a pas donné les résultats souhaités.To eliminate the coalescence which occurs during heat treatment, it has been proposed, in the prior art, to produce the scintillator of the input screen by evaporating alternately pure cesium iodide and cesium iodide doped with refractory material. It was hoped that needles thus formed by alternating layers of pure cesium iodide and cesium iodide doped with a refractory material would not come into contact during the heat treatment. This solution did not give the desired results.

La présente invention propose de résoudre le problème posé par le traitement thermique de la façon suivante. Selon l'invention, les aiguilles d'iodure de césium du scintillateur sont enrobées par un matériau réfractaire, transparent ou réféchis- sant, et d'indice optique voisin ou inférieur à celui de l'iodure de césium. Du fait de cet enrobage, on n'observe pas de coalescence des aiguilles lors du traitement thermique ultérieur à l'enrobage, qui assure la luminescence de l'écran.The present invention proposes to solve the problem posed by the heat treatment in the following manner. According to the invention, the cesium iodide needles of the scintillator are coated with a refractory material, transparent or reflective, and with an optical index close to or less than that of cesium iodide. Due to this coating, the needles are not coalesced during the heat treatment subsequent to the coating, which ensures the luminescence of the screen.

L'invention a aussi pour objet des procédés de fabrication d'un tel scintillateur.The invention also relates to methods of manufacturing such a scintillator.

La description suivante est illustrée par :

  • - les figures 1 et 2, deux schémas montrant un scintillateur d'écran d'entrée de tube intensificateur d'images radiologiques, selon l'art antérieur ;
  • - la figure 3, un schéma montrant un scintillateur d'écran d'entrée de tube intensificateur d'images radiologiques, selon l'invention
  • - la figure 4, deux courbes montrant l'amélioration de la fonction de transfert de modulation (F.T.M.), apportée par l'invention.
The following description is illustrated by:
  • - Figures 1 and 2, two diagrams showing an input screen scintillator of radiological image intensifier tube, according to the prior art;
  • - Figure 3, a diagram showing a scintillator of input screen of tube intensifier of radiological images, according to the invention
  • - Figure 4, two curves showing the improvement of the modulation transfer function (FTM), provided by the invention.

Les figures 1 et 2 ont été décrites dans l'introduction et la description.Figures 1 and 2 have been described in the introduction and description.

La figure 3 représente de façon schématique un scintillateur d'écran d'entrée de tube intensificateur d'images radiologiques selon l'invention. Comme sur les figures 1 et 2, on a représenté un substrat 1, en aluminium par exemple, portant quelques aiguilles en iodure de césium. Selon l'invention, des aiguilles 2 sont enrobées par un matériau réfractaire 5, transparent et d'indice optique voisin ou inférieur à celui de l'iodure de césium.FIG. 3 schematically represents a screen scintillator of an X-ray image intensifier tube according to the invention. As in Figures 1 and 2, there is shown a substrate 1, made of aluminum for example, carrying a few needles of cesium iodide. According to the invention, needles 2 are coated with a refractory material 5, transparent and with an optical index close to or less than that of cesium iodide.

Les aiguilles sont donc enrobées par un matériau qui vient s'insérer dans les interstices entre les aiguilles et qui agit comme une barrière mécanique en conservant les aiguilles isolées les unes des autres lors du traitement thermique ultérieur, destiné à assurer la luminescence de l'écran. Ce matériau doit être réfractaire, c'est-à-dire avoir un point de fusion aussi élevé que possible pour ne pas être affecté par le traitement thermique. Il doit être transparent ou réfléchissant pour ne pas absorber la lumière. Enfin, ce matériau doit avoir un indice optique voisin ou inférieur à celui de l'iodure de césium de façon à conserver un effet de fibres optiques.The needles are therefore coated with a material which is inserted into the interstices between the needles and which acts as a mechanical barrier by keeping the needles isolated from each other during the subsequent heat treatment, intended to ensure the luminescence of the screen. . This material must be refractory, that is to say have a melting point as high as possible so as not to be affected by the heat treatment. It must be transparent or reflective so as not to absorb light. Finally, this material must have an optical index close to or lower than that of cesium iodide so as to maintain an effect of optical fibers.

Le procédé utilisé pour réaliser cet enrobage détermine la nature du matériau utilisé comme on va le voir dans la suite de la description. Ainsi, le matériau d'enrobage 5 peut être un oxyde d'un métal ou d'un non-métal, une résine polymérisable du type silicone, un composé organo-métallique, etc...The process used to carry out this coating determines the nature of the material used as will be seen in the following description. Thus, the coating material 5 may be an oxide of a metal or of a non-metal, a polymerizable resin of the silicone type, an organometallic compound, etc.

Sur la figure 4, les courbes 6 et 7 montrent, en fonction de la fréquence spatiale, en paires de lignes par centimètre que la fonction de transfert de modulation (F.T.M.), en pourcentage, est plus élevée dans le cas du scintillateur selon l'invention, courbe 7, que dans le cas d'un scintillateur selon l'art antérieur, courbe 6. L'invention permet donc d'obtenir une haute résolution et une F.T.M. élevée.In FIG. 4, curves 6 and 7 show, as a function of the spatial frequency, in pairs of lines per centimeter that the modulation transfer function (FTM), in percentage, is higher in the case of the scintillator according to the invention, curve 7, than in the case of a scintillator according to the prior art, curve 6. The invention therefore makes it possible to obtain a high resolution and an FTM high.

Divers procédés peuvent être utilisés pour réaliser l'écran selon l'invention. L'un de ces procédés est un dépôt chimique en phase vapeur, couramment appelé C.V.D. pour "chemical vapour deposi- tion". Ce procédé est couramment utilisé dans le domaine des semi-conducteurs pour déposer un matériau en couche mince sur un substrat plan. Selon l'invention, on utilise ce procédé pour déposer un matériau en couche mince sur un substrat essentiellement vertical constitué par chaque aiguille du scintillateur. Il faut souligner que la difficulté de réalisation de l'enrobage des aiguilles provient du fait que les interstices entre aiguilles ont une grande longueur par rapport à leur diamètre, leur longueur étant approximativement mille fois plus grande que leur diamètre.Various methods can be used to make the screen according to the invention. One such process is chemical vapor deposition, commonly known as C.V.D. for "chemical vapor deposition". This method is commonly used in the field of semiconductors for depositing a thin film material on a flat substrate. According to the invention, this method is used to deposit a material in a thin layer on an essentially vertical substrate constituted by each needle of the scintillator. It should be emphasized that the difficulty in achieving the coating of the needles arises from the fact that the interstices between needles have a great length with respect to their diameter, their length being approximately a thousand times greater than their diameter.

Le matériau d'enrobage déposé par ce procédé peut être tout oxyde d'un métal ou d'un non-métal qui soit réfractaire, transparent - ou réfléchissant, et d'indice optique voisin ou inférieur à celui de l'iodure de césium. Le matériau d'enrobage utilisé peut avoir l'une des formules suivantes : Si 0, Si 02 , Si Ox avec 1 < x <2,AI2O3, Sb2O5...The coating material deposited by this process can be any oxide of a metal or of a non-metal which is refractory, transparent - or reflective, and with an optical index close to or less than that of cesium iodide. The coating material used can have one of the following formulas: Si 0, Si 0 2 , Si O x with 1 <x <2, AI 2 O 3 , Sb 2 O 5 ...

Diverses variantes du procédé C.V.D. peuvent être utilisées. Selon ces variantes, l'activation du procédé C.V.D. est réalisée de différentes façons.Various variants of the C.V.D. can be used. According to these variants, the activation of the C.V.D. is done in different ways.

Ainsi, l'activation du procédé C.V.D. peut être réalisée par excitation thermique : c'est le C.V.D. haute température. Il comporte une mise sous vide initiale, suivie par une mise à la pression atmosphérique. On réalise un dépôt réactif en phase vapeur en utilisant un mélange de gaz tels que du silane Si H4 . de l'oxygène, et de l'oxyde d'azote N2 O. Les molécules du mélange se recombinent pour former de la silice Si 02 qui se dépose sur les aiguilles d'iodure de césium. Il est également possible de déposer du nitrure de silicium Si3 N4 par le même type de procédé. Le C.V.D. haute température impose d'utiliser une température supérieure à 300" C.Thus, the activation of the CVD process can be carried out by thermal excitation: this is the high temperature CVD. It includes initial vacuuming, followed by atmospheric pressure. Reactive vapor deposition is carried out using a mixture of gases such as silane Si H 4 . oxygen, and nitrogen oxide N 2 O. The molecules of the mixture recombine to form silica Si 0 2 which is deposited on the needles of cesium iodide. It is also possible to deposit silicon nitride Si 3 N 4 by the same type of process. The high temperature CVD requires using a temperature above 300 "C.

L'activation du procédé C.V.D. peut aussi être réalisée par excitation plasma, vers 100"C, ou par excitation photonique, vers 100° C aussi. Dans le cas de l'excitation photonique, la couche d'enrobage peut être du nitrure de silicium Si3 N4 . L'activation du procédé C.V.D. peut aussi être réalisée par l'utilisation d'un procédé haute température plus basse pression (Technique LPCVD).The activation of the CVD process can also be carried out by plasma excitation, around 100 "C, or by photonic excitation, around 100 ° C. Also. In the case of photonic excitation, the coating layer can be silicon nitride If 3 N 4. Activation of the CVD process can also be achieved by the use of a lower pressure high temperature process (LPCVD technique).

Un autre procédé pour réaliser l'écran selon l'invention peut être l'enrobage par diffusion d'une solution colloïdale à l'intérieur des interstices entre aiguilles. On peut utiliser une solution colloïdale de Si 02 , ou d'AI2 03 , Sb2 Os . Sn 04 , par exemple .Another method for producing the screen according to the invention can be the coating by diffusion of a colloidal solution inside the interstices between needles. A colloidal solution of Si 0 2 , or of AI 2 0 3 , Sb 2 Os can be used. Sn 0 4 , for example.

L'enrobage par diffusion est suivi d'un traitement thermique qui provoque le dépôt du matériau d'enrobage, par exemple Si 02 dans le cas d'une solution colloïdale de Si 02 . Ce traitement thermique peut être réalisé en même temps que le traitement thermique destiné à provoquer la luminescence des aiguilles d'iodure de césium.The diffusion coating is followed by a heat treatment which causes the deposition of the coating material, for example Si 0 2 in the case of a colloidal solution of Si 0 2 . This heat treatment can be carried out at the same time as the heat treatment intended to cause the luminescence of the cesium iodide needles.

Un autre procédé pour réaliser l'écran selon l'invention est l'enrobage sous vide par une résine polymère du type silicone ou tout matériau polyimide. Le durcissement du matériau d'enrobage se produit soit à la température ambiante. soit à chaud.Another process for producing the screen according to the invention is the vacuum coating with a polymer resin of the silicone type or any polyimide material. Curing of the coating material occurs either at room temperature. either hot.

Un dernier procédé consiste à réaliser l'enrobage par diffusion d'un composé organo-métallique dans les interstices entre les aiguilles. On peut citer comme exemple d'un tel composé le tétraméthoxy- silane, le tétra-éthoxy-silane ou le silicium tétra-acétate. Ce composé organo-métallique doit subir un traitement à haute température ou une hydrolyse à l'air.A final method consists in carrying out the coating by diffusion of an organo-metallic compound in the interstices between the needles. An example of such a compound that may be mentioned is tetramethoxy-silane, tetra-ethoxy-silane or silicon tetra-acetate. This organometallic compound must undergo treatment at high temperature or hydrolysis in air.

Claims (12)

1. Scintillateur d'écran d'entrée de tube intensificateur d'images rpdiologiques, constitué par la juxtaposition d'aiguilles (2) en iodure de césium, caractérisé en ce que ces aiguilles (2) sont enrobées par un matériau (5) réfractaire, transparent ou réfléchissant et d'indice optique voisin ou inférieur à celui de l'iodure de césium.1. Input screen scintillator for intensifier tube of radiological images, constituted by the juxtaposition of needles (2) of cesium iodide, characterized in that these needles (2) are coated with a refractory material (5) , transparent or reflective and with an optical index close to or less than that of cesium iodide. 2. Scintillateur selon la revendication 1, caractérisé en ce que le matériau d'enrobage (5) des aiguilles (2) est un oxyde d'un métal ou d'un non métal.2. Scintillator according to claim 1, characterized in that the coating material (5) of the needles (2) is an oxide of a metal or of a non-metal. 3. Scintillateur selon la revendication 1, caractérisé en ce que ce matériau d'enrobage a l'une des formules suivantes : Si 0, Si 02, Si Ox avec 1 < x < 2 , AI2 03 , Sb2 O5, Si3 N4, Sn04.3. Scintillator according to claim 1, characterized in that this coating material has one of the following formulas: Si 0, Si 02, Si O x with 1 <x <2, AI2 0 3 , Sb 2 O 5 , If 3 N 4 , Sn04. 4. Procédé de fabrication d'un scintillateur d'écran d'entrée de tube intensificateur d'images radiologiques, constitué par la juxtaposition d'aiguilles (2) en iodure de césium, caractérisé en ce que : - on enrobe les aiguilles (2) par un matériau (5) réfractaire, transparent ou réfléchissant, et d'indice optique voisin ou inférieur à celui de l'iodiure de césium ; - on réalise ensuite le traitement thermique qui assure la luminescence de l'écran. 4. Method for manufacturing a scintillator for an input screen of a radiological image intensifier tube, constituted by the juxtaposition of needles (2) of cesium iodide, characterized in that - The needles (2) are coated with a refractory, transparent or reflective material (5) and with an optical index close to or less than that of cesium iodide; - then the heat treatment is carried out which ensures the luminescence of the screen. 5. Procédé de fabrication d'un scintillateur selon la revendication 4. caractérisé en ce que le matériau d'enrobage (5) des aiguilles (2) est déposé par dépôt chimique en phase vapeur.5. A method of manufacturing a scintillator according to claim 4. characterized in that the coating material (5) of the needles (2) is deposited by chemical vapor deposition. 6. Procédé de fabrication d'un scintillateur selon la revendication 4, caractérisé en ce que le matériau d'enrobage (5) des aiguilles (2) est déposé par dépôt chimique en phase vapeur, activé par excitation thermique, ce matériau d'enrobage étant de la silice Si 02 ou du nitrure de Silicium Si3 N4.6. A method of manufacturing a scintillator according to claim 4, characterized in that the coating material (5) of the needles (2) is deposited by chemical vapor deposition, activated by thermal excitation, this coating material being silica Si 0 2 or silicon nitride Si 3 N 4 . 7. Procédé de fabrication d'un scintillateur selon la revendication 4, caractérisé en ce que le matériau d'enrobage (5) des aiguilles (2) est déposé par dépôt chimique en phase vapeur, activé par excitation plasma ou par excitation photonique ou par l'utilisation de basse pression et haute température.7. A method of manufacturing a scintillator according to claim 4, characterized in that the coating material (5) of the needles (2) is deposited by chemical vapor deposition, activated by plasma excitation or by photon excitation or by the use of low pressure and high temperature. 8. Procédé de fabrication d'un scintillateur selon la revendication 4, caractérisé en ce que le matériau d'enrobage (5) est déposé par diffusion d'une solution colloïdale à l'intérieur des interstices entre aiguilles (2), suivie par un traitement thermique provoquant le dépôt du matériau d'enrobage.8. A method of manufacturing a scintillator according to claim 4, characterized in that the coating material (5) is deposited by diffusion of a colloidal solution inside the interstices between needles (2), followed by a heat treatment causing the deposition of the coating material. 9. Procédé selon la revendication 8, caractérisé en ce que la solution colloïdale utilisée a l'une des formules suivantes : Si 02 , AI2 Os . Sb2 O5, Sn 04 .9. Method according to claim 8, characterized in that the colloidal solution used has one of the following formulas: Si 0 2 , AI2 Os. Sb 2 O 5 , Sn 0 4 . 10. Procédé de fabrication d'un scintillateur selon la revendication 4, caractérisé en ce que l'enrobage des aiguilles (2) d'iodure de césium est fait sous vide par une résine polymère du type silicone ou tout matériau polyimide, le durcissement du matériau d'enrobage étant réalisé ultérieurement soit à la température ambiante, soit à chaud.10. A method of manufacturing a scintillator according to claim 4, characterized in that the coating of the needles (2) of cesium iodide is done under vacuum with a polymeric resin of the silicone type or any polyimide material, the hardening of the coating material being produced subsequently either at room temperature or hot. 11. Procédé de fabrication d'un scintillateur selon la revendication 4, caractérisé en ce que l'enrobage des aiguilles (2) d'iodure de césium est fait par diffusion, entre les aiguilles, d'un composé organo-métallique subissant ensuite un traitement à haute température ou une hydrolyse à l'air.11. A method of manufacturing a scintillator according to claim 4, characterized in that the coating of the needles (2) of cesium iodide is made by diffusion, between the needles, of an organometallic compound then undergoing a high temperature treatment or air hydrolysis. 12. Procédé selon la revendication 11, caractérisé en ce qu'on utilise l'un des composés organo-métalliques suivants : tétra-méthoxy-silane, ou tétra-éthoxy-silane, ou silicium tétra- acétate.12. Method according to claim 11, characterized in that one of the following organometallic compounds is used: tetra-methoxy-silane, or tetra-ethoxy-silane, or silicon tetra-acetate.
EP86401835A 1985-08-23 1986-08-19 Scintillator input screen for an x-ray image intensifier, and method of manufacturing such a scintillator Expired EP0215699B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8512688 1985-08-23
FR8512688A FR2586508B1 (en) 1985-08-23 1985-08-23 RADIOLOGICAL IMAGE ENHANCER TUBE ENTRY SCREEN SCINTILLER AND METHOD FOR MANUFACTURING SUCH A SCINTILLATOR

Publications (2)

Publication Number Publication Date
EP0215699A1 true EP0215699A1 (en) 1987-03-25
EP0215699B1 EP0215699B1 (en) 1989-06-21

Family

ID=9322367

Family Applications (1)

Application Number Title Priority Date Filing Date
EP86401835A Expired EP0215699B1 (en) 1985-08-23 1986-08-19 Scintillator input screen for an x-ray image intensifier, and method of manufacturing such a scintillator

Country Status (5)

Country Link
US (1) US4803366A (en)
EP (1) EP0215699B1 (en)
JP (1) JP2571771B2 (en)
DE (1) DE3664079D1 (en)
FR (1) FR2586508B1 (en)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2625838A1 (en) * 1988-01-13 1989-07-13 Thomson Csf INTENSIFIER RADIOLOGICAL IMAGE INTENSIFIER TUBE ENTRY SCINTILLATOR AND METHOD FOR MANUFACTURING SUCH A SCINTILLATOR
EP0352152A1 (en) * 1988-07-22 1990-01-24 Thomson-Csf Method of manufacturing a scintillator, and scintillator so obtained
EP0372395A2 (en) * 1988-12-02 1990-06-13 Kabushiki Kaisha Toshiba X-ray image intensifier and method of manufacturing the same
EP0413482A2 (en) * 1989-08-18 1991-02-20 Galileo Electro-Optics Corp. Thin-film continuous dynodes
DE10116803A1 (en) * 2001-04-04 2002-10-17 Siemens Ag Radiation converter and method of manufacturing the same

Families Citing this family (22)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL8602629A (en) * 1986-10-21 1988-05-16 Philips Nv ROENTGEN IMAGE AMPLIFIER TUBE WITH A SEPARATION LAYER BETWEEN THE LUMINESCENTION LAYER AND THE PHOTOCATHODE.
JPS63262600A (en) * 1987-04-20 1988-10-28 富士写真フイルム株式会社 Radiation picture conversion panel and manufacture thereof
JP3297078B2 (en) * 1991-05-24 2002-07-02 株式会社東芝 X-ray image tube and method of manufacturing the same
US6037274A (en) 1995-02-17 2000-03-14 Fujitsu Limited Method for forming insulating film
DE19516450C1 (en) * 1995-05-04 1996-08-08 Siemens Ag Prodn. of phosphor layer in vaporising appts.
US7019301B2 (en) * 1997-02-14 2006-03-28 Hamamatsu Photonics K.K. Radiation detection device and method of making the same
AU4168699A (en) 1998-06-18 2000-01-05 Hamamatsu Photonics K.K. Method of organic film deposition
FR2782388B1 (en) 1998-08-11 2000-11-03 Trixell Sas SOLID STATE RADIATION DETECTOR WITH INCREASED LIFE
DE10141522C1 (en) * 2001-08-24 2003-03-06 Siemens Ag Process for producing a phosphor layer
JP2003075593A (en) * 2001-08-30 2003-03-12 Toshiba Corp Radiation scintillator, image detector and manufacturing method thereof
DE10301274B4 (en) * 2003-01-15 2005-03-24 Siemens Ag Method for producing an image converter with a needle-shaped phosphor layer
US7112802B2 (en) * 2003-04-11 2006-09-26 Canon Kabushiki Kaisha Scintillator panel, radiation detecting apparatus, and radiation detection system
US6934453B2 (en) * 2003-11-06 2005-08-23 General Electric Company Fiber optic brush light detector and method
DE102004026842B4 (en) * 2004-06-02 2007-12-27 Siemens Ag X-ray detector
FR2888045B1 (en) * 2005-07-01 2007-10-19 Thales Sa IMAGE SENSOR WITH IMPROVED SPATIAL RESOLUTION AND SENSOR PRODUCTION METHOD
US7482602B2 (en) * 2005-11-16 2009-01-27 Konica Minolta Medical & Graphic, Inc. Scintillator plate for radiation and production method of the same
US20090084982A1 (en) * 2005-11-18 2009-04-02 Shinji Kudo Radiation scintillator plate
CN103254896B (en) * 2006-03-21 2015-01-21 超点公司 Luminescent materials that emit light in the visible range or the near infrared range
WO2008118523A2 (en) * 2007-03-26 2008-10-02 General Electric Company Scintillators and method for making same
US8124945B2 (en) * 2007-04-05 2012-02-28 Konica Minolta Medical & Graphic, Inc. Scintillator plate
EP2510073B1 (en) 2009-12-08 2017-07-05 Omnipv, Inc. Luminescent materials that emit light in the visible range or the near infrared range and methods of forming thereof
JP5947499B2 (en) * 2011-07-26 2016-07-06 キヤノン株式会社 Radiation detector

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3838273A (en) * 1972-05-30 1974-09-24 Gen Electric X-ray image intensifier input
US4069355A (en) * 1975-04-28 1978-01-17 General Electric Company Process of making structured x-ray phosphor screen
FR2360989A1 (en) * 1976-08-03 1978-03-03 Thomson Csf RADIOLOGICAL IMAGE INTENSIFIER, AND ITS MANUFACTURING PROCESS
US4100445A (en) * 1976-03-15 1978-07-11 The Machlett Laboratories, Inc. Image output screen comprising juxtaposed doped alkali-halide crystalline rods
EP0042149A1 (en) * 1980-06-16 1981-12-23 Kabushiki Kaisha Toshiba Radiation excited phosphor screen and method for manufacturing the same

Family Cites Families (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS52109858A (en) * 1976-03-11 1977-09-14 Toshiba Corp X-ray image intensifier
JPS5346631A (en) * 1976-10-07 1978-04-26 Matsushita Electric Ind Co Ltd Manufacturing method of flyback transformer
US4100455A (en) * 1976-10-14 1978-07-11 Wagner Electric Corporation Vacuum fluorescent display device with circular polarizer
US4101781A (en) * 1977-06-27 1978-07-18 Hewlett-Packard Company Stable fiber optic scintillative x-ray screen and method of production
JPS5440071A (en) * 1977-09-05 1979-03-28 Sharp Corp Electronic timer device
JPS5632649A (en) * 1979-08-23 1981-04-02 Shimadzu Corp Input screen of image tube
JPS5719859U (en) * 1980-07-08 1982-02-02
JPS58131644A (en) * 1981-12-26 1983-08-05 Toshiba Corp Input screen of radiation image multiplier tube and its manufacture

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3838273A (en) * 1972-05-30 1974-09-24 Gen Electric X-ray image intensifier input
US4069355A (en) * 1975-04-28 1978-01-17 General Electric Company Process of making structured x-ray phosphor screen
US4100445A (en) * 1976-03-15 1978-07-11 The Machlett Laboratories, Inc. Image output screen comprising juxtaposed doped alkali-halide crystalline rods
FR2360989A1 (en) * 1976-08-03 1978-03-03 Thomson Csf RADIOLOGICAL IMAGE INTENSIFIER, AND ITS MANUFACTURING PROCESS
EP0042149A1 (en) * 1980-06-16 1981-12-23 Kabushiki Kaisha Toshiba Radiation excited phosphor screen and method for manufacturing the same

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4980561A (en) * 1988-01-13 1990-12-25 Thomson-Csf Input screen scintillator for an X-ray image intensifier tube and manufacturing process of this scintillator
EP0325500A1 (en) * 1988-01-13 1989-07-26 Thomson-Csf Input screen scintillator for a radiological image intensifier tube and its manufacturing method
US5298294A (en) * 1988-01-13 1994-03-29 Thomson-Csf Input screen scintillator for an X-ray image intensifier tube and manufacturing process of this scintillator
FR2625838A1 (en) * 1988-01-13 1989-07-13 Thomson Csf INTENSIFIER RADIOLOGICAL IMAGE INTENSIFIER TUBE ENTRY SCINTILLATOR AND METHOD FOR MANUFACTURING SUCH A SCINTILLATOR
FR2634562A1 (en) * 1988-07-22 1990-01-26 Thomson Csf METHOD FOR MANUFACTURING A SCINTILLATOR AND SCINTILLATOR THUS OBTAINED
US4985633A (en) * 1988-07-22 1991-01-15 Thomson-Csf Scintillator with alveolate structured substrate
EP0352152A1 (en) * 1988-07-22 1990-01-24 Thomson-Csf Method of manufacturing a scintillator, and scintillator so obtained
EP0372395A3 (en) * 1988-12-02 1990-10-31 Kabushiki Kaisha Toshiba X-ray image intensifier and method of manufacturing the same
EP0372395A2 (en) * 1988-12-02 1990-06-13 Kabushiki Kaisha Toshiba X-ray image intensifier and method of manufacturing the same
US5083017A (en) * 1988-12-02 1992-01-21 Kabushiki Kaisha Toshiba X-ray image intensifier with unitary plate input phosphor screen
EP0413482A2 (en) * 1989-08-18 1991-02-20 Galileo Electro-Optics Corp. Thin-film continuous dynodes
EP0413482A3 (en) * 1989-08-18 1991-07-10 Galileo Electro-Optics Corp. Thin-film continuous dynodes
DE10116803A1 (en) * 2001-04-04 2002-10-17 Siemens Ag Radiation converter and method of manufacturing the same
DE10116803C2 (en) * 2001-04-04 2003-10-02 Siemens Ag Radiation converter and method of making the same

Also Published As

Publication number Publication date
US4803366A (en) 1989-02-07
JPS6273538A (en) 1987-04-04
EP0215699B1 (en) 1989-06-21
FR2586508A1 (en) 1987-02-27
DE3664079D1 (en) 1989-07-27
FR2586508B1 (en) 1988-08-26
JP2571771B2 (en) 1997-01-16

Similar Documents

Publication Publication Date Title
EP0215699B1 (en) Scintillator input screen for an x-ray image intensifier, and method of manufacturing such a scintillator
EP0042149B1 (en) Radiation excited phosphor screen and method for manufacturing the same
JPS5944738B2 (en) Manufacturing method of luminescent screen
EP0325500B1 (en) Input screen scintillator for a radiological image intensifier tube and its manufacturing method
US6455860B1 (en) Resolution enhancement device for an optically-coupled image sensor using high extra-mural absorbent fiber
EP0352152B1 (en) Method of manufacturing a scintillator, and scintillator so obtained
US5047624A (en) Method of manufacturing and X-ray image intensifier
EP0403802B1 (en) X-ray image intensifier and method of manufacturing input screen
US4563614A (en) Photocathode having fiber optic faceplate containing glass having a low annealing temperature
US5460980A (en) Process for forming a phosphor
FR2647955A1 (en) RADIOLOGICAL IMAGE INTENSIFIER TUBE INPUT SCREEN
US11181650B2 (en) Scintillator plate, radiation imaging apparatus, and method of manufacturing scintillator plate
JPS5941267B2 (en) Radiation-excited fluorescent surface and its manufacturing method
EP0170310B1 (en) Inlayed cathodoluminescent screen with restored cavities, and visualisation tube with such a screen
EP0553578A1 (en) Image intensifier tube with intensity distribution compensation
FR2555321A1 (en) Scintillation device for detecting X-rays
JPH0362437A (en) X-ray image tube
EP0143714A1 (en) Luminescent screen and process for manfacturing the same
FR2525406A1 (en) Electron beam laser tube - has screen with reflectively coated semiconductor plate with metal and transparent dielectric oxide layers
JPH04154032A (en) X-ray fluorescent image intensifying tube

Legal Events

Date Code Title Description
PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

Free format text: ORIGINAL CODE: 0009012

AK Designated contracting states

Kind code of ref document: A1

Designated state(s): DE GB NL

17P Request for examination filed

Effective date: 19870406

17Q First examination report despatched

Effective date: 19880629

GRAA (expected) grant

Free format text: ORIGINAL CODE: 0009210

RAP3 Party data changed (applicant data changed or rights of an application transferred)

Owner name: THOMSON-CSF

AK Designated contracting states

Kind code of ref document: B1

Designated state(s): DE GB NL

REF Corresponds to:

Ref document number: 3664079

Country of ref document: DE

Date of ref document: 19890727

GBT Gb: translation of ep patent filed (gb section 77(6)(a)/1977)
PLBE No opposition filed within time limit

Free format text: ORIGINAL CODE: 0009261

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: NO OPPOSITION FILED WITHIN TIME LIMIT

26N No opposition filed
PGFP Annual fee paid to national office [announced via postgrant information from national office to epo]

Ref country code: GB

Payment date: 19960719

Year of fee payment: 11

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: GB

Free format text: LAPSE BECAUSE OF NON-PAYMENT OF DUE FEES

Effective date: 19970819

GBPC Gb: european patent ceased through non-payment of renewal fee

Effective date: 19970819

PGFP Annual fee paid to national office [announced via postgrant information from national office to epo]

Ref country code: NL

Payment date: 20050803

Year of fee payment: 20

PGFP Annual fee paid to national office [announced via postgrant information from national office to epo]

Ref country code: DE

Payment date: 20050811

Year of fee payment: 20

PG25 Lapsed in a contracting state [announced via postgrant information from national office to epo]

Ref country code: NL

Free format text: LAPSE BECAUSE OF EXPIRATION OF PROTECTION

Effective date: 20060819

NLV7 Nl: ceased due to reaching the maximum lifetime of a patent

Effective date: 20060819