EP0187258B1 - X-ray image intensifier - Google Patents

Description

The invention relates to X-ray image intensifiers according to the preamble of claim 1. Such X-ray image intensifiers are known from US Pat. No. 3,458,744.

In the case of electronic image intensifiers of the type mentioned in the aforementioned patent document, X-ray images are known to be converted into electron images, which are then subjected to an acceleration voltage and, if necessary, are imaged on an output screen in a reduced electron-optical format. In the case of X-ray image intensifiers, which are generally of a single-stage design and in which the electron image is reproduced in a reduced form, the image which appears on the output screen is also the one which is viewed. However, this presupposes that the exit screen can be seen through the wall of the piston of the image intensifier. The piston has therefore been made of transparent material, in particular glass, at least at this point.

In order to obtain an expediently manageable constructive solution, the window inserted into the bulb was simultaneously made the carrier of the exit fluorescent screen. Since in the known constructive solution the exit window is gripped into a metal frame by melting, the fluorescent screen can only be applied after this activity. However, this is disadvantageous because, when coated with the luminescent layer, the yield of screens that can be used later is low, so that the precise connection of the glass pane to the frame has to be made in many cases on panes that later only lead to unusable screens.

US-A-3 173 201 describes a method for connecting glass to metal. So that the glass can be soldered to the metal, metal layers are applied by vapor deposition at the locations provided for the soldering. A statement about the soldering material used is not affected. The method also does not relate to a vacuum-tight connection of a pane coated with a phosphor to a metal tube.

In GB-PS 1 482 696 a method for pressure welding a seal of a glass front plate with a metal cone of an electronic display tube is described, in which the glass is connected to the metal by a flexible metal layer, which under high pressure at temperatures below the melting point connects both materials together. Either a lead-silver-tin or a lead-indium alloy can be considered as materials. A disadvantage here is the complex manufacturing process.

The invention has for its object to provide an X-ray image intensifier of the type mentioned, in which the finished output screen can be gripped in a metal frame and used in the wall of the vacuum piston as the output window. This object is achieved in an image intensifier according to the preamble of claim 1 by the features mentioned in its characterizing part. Appropriate developments and refinements are the subject of the dependent claims.

By using a soft solder for soldering the window pane into a metal frame, which can be inserted into the window opening of the vacuum piston of an image intensifier by means of a flange, i. H. of a solder whose melting temperature is between 250 and 400 ° C, on the one hand, at the lowest possible temperature, on the other hand, a solder that withstands the baking out of the image intensifier is obtained. To protect the fluorescent screen, it is expediently carried out in an inert medium, for example by soldering in a hydrogen atmosphere or in another protective gas or in a vacuum. The luminous efficiency of the luminescent layer that can be achieved during later operation of the image intensifier is not yet impaired.

In the manufacturing and operating conditions, stable metals are suitable for the metal frame, which can be tightly connected to the material of the exit window as well as to that of the tube bulb. For use in glass pistons, those have proven to be useful which have nickel (Ni), iron (Fe) or Ni, chromium (Cr), Fe or Ni, cobalt (Co), Fe or Ni, Co, Cr, Fe as main components contain. They are iron alloys that contain between 20 and 60% Ni and / or 10 to 30% Co and / or 1 to 10% Cr.

Solders based on lead (Pb) have proven useful for soldering. These solders have the advantage over others that their processing temperature, ie also their softening, is significantly higher than the temperature which is necessary for the degassing heating of the image intensifier tube in the course of production. However, it is still below a temperature which is detrimental to the luminosity of the luminous pigment.

In addition to lead, alloys have proven themselves, in which lead is alloyed with silver (Ag), tin (Sn) or indium (In). The additives are added to the lead, for example in amounts ranging from 0.1 percent by weight to 10 percent by weight, so that, on the one hand, the addition can have an effect with small amounts and, on the other hand, in the case of high amounts added, there is no increase in the melting temperature and the formation of the soldering aggravating material inhomogeneities. An alloy of lead and 2.5 percent by weight of silver has proven to be favorable.

The wetting and adhesion of the solder to parts to be connected can be promoted by adapting their surfaces, for example by simply coating or covering them with a system of layers of coordinated materials. A simple adhesive layer or the For glass, the first layer of a suitable layer sequence should consist of a substance that has a high affinity for oxygen, since the connection to the glass surface is established via metal oxide. Both the metal of the coating and the oxide formed on the border must have sufficient tensile strength for the desired fastening.

The second layer is a protective layer for the first layer and can also be a solder layer. The second layer must stop the flow of solder in such a way that it does not separate from the first.

The third layer protects the first two from oxidation and can also be a solder layer.

• 1. Schicht : Titan (Ti), Niob (Nb), Tantal (Ta), NiCr, Cr, Fe,
• 2. Schicht : Ni, Gold (Au), Platin (Pt), Molybdän (Mo), Fe und für die
• 3. Schicht : Au, Silber (Ag), Ni, Kupfer (Cu), Pt, Palladium (Pd).

Suitable materials are for the

• 1st layer: titanium (Ti), niobium (Nb), tantalum (Ta), NiCr, Cr, Fe,
• 2nd layer: Ni, gold (Au), platinum (Pt), molybdenum (Mo), and for the
• 3rd layer: Au, silver (Ag), Ni, copper (Cu), Pt, palladium (Pd).

Suitable systems of coordinated layers can e.g. B. for the soldering of a glass pane consist of layer sequences in which chromium is first evaporated to a thickness of 30 to 300 nm. When this layer is deposited under high vacuum, it can be assumed that the metallic chromium reacts with oxygen in the vapor phase and on the glass surface or with thin oxide coatings. The actual adhesion thus arises from a very thin layer of chromium oxide, which cannot be defined in its composition. This first layer can then be followed by a second layer made of nickel and then the third layer made of silver, the thickness of which corresponds to that of chrome.

However, the chromium layer can also be coated with iron, which is coated with nickel and then followed by a nickel-nickel alloy, or an iron-chromium-nickel alloy or a chromium-nickel alloy is evaporated. When stratification, it is only necessary to ensure that the layers closest to the glass are built up in the order of chromium oxide-chromium.A layer of at least 30 nm thick consists of pure chromium, since this does not form solid solutions with lead, and that the top layer is made of nickel, respectively Ag exists because there is good solubility of lead and therefore good bondability with the solder. Finally, the entire layer that improves adhesion can be covered with gold. With sufficient tightness, which can be achieved at thicknesses of approximately 400 nm, this causes oxidation of the top layer, i. H. such as the formation of nickel or silver oxide is avoided.

The metal frame can also be provided with the above-mentioned adhesive layers or layering on its surfaces to be soldered. Particularly when using Niromed 44 or Vacon 20 or Vacon 70 as frame material, good adhesion of the solder is also achieved on this part. The actual soldering is preferably carried out in a high vacuum with layer thicknesses of 100 to 300 nm per individual layer. Soldering is carried out at temperatures of around 350 ° C and instead of the high vacuum, a protective gas atmosphere, such as one made of hydrogen, can also be used.

• In der Figur 1 ist der Querschnitt durch einen schematisch dargestellten einstufigen Vakuumröntgenbildverstärker gezeichnet,
• in der Figur 2 eine Ausschnitt aus der Verbindung des Ausgangsfensters mit dem elektronischen Vakuumkolben des Bildverstärkers und
• in den Figuren 3 bis 5 verschiedene Ausführungsformen von Haftschichten am Ausgangsfenster.

Further details and advantages of the invention are further explained below using the exemplary embodiments shown in the figures.

• 1 shows the cross section through a schematically illustrated single-stage vacuum X-ray image intensifier,
• in Figure 2 shows a section of the connection of the output window with the electronic vacuum piston of the image intensifier and
• in Figures 3 to 5 different embodiments of adhesive layers at the exit window.

In FIG. 1, 1 denotes the vacuum piston of an X-ray image intensifier. This piston 1 consists of a cathode cap 2, which closes an opening of a ceramic body 3 representing a stepped diameter, the other opening of which is smaller than the first smaller diameter and is closed by an anode attachment 4. Inside the piston 1 is the known structure of an electronic image intensifier, i.e. H. on the inner wall of the cap 2 opposite the attachment 4 there is a luminescent layer 5 which is covered with a photocathode layer 6. This is followed by electron-optical electrodes 7 and 8, which are fastened to the ceramic body 3, and finally the actual anode 9. At the end of the outward opening of the anode 9, the disc 12 on the frame 11 of the exit window is inserted by means of soldering 10. The disk 12 carries the exit fluorescent screen 13 on its inside and is connected to the frame 11 in a vacuum-tight manner with a solder joint 14.

As is known, the mode of operation of the image intensifier is based on the fact that x-ray images penetrating the luminous layer 5 through the wall of the cap 2 trigger an electron image in the photocathode 6. This is then imaged onto the luminescent layer 13 by means of the electrodes 7 and 8 and the anode 9, in that the corresponding potentials are applied to the cap 2, the connecting lines 15 and 16, to the electrodes 7 and 8 and to the attachment 4 for the anode 9 will.

From Figure 2 it can be seen that the solder joint 14 between the disc 12 and the inside of the frame 11 made of adhesive layers. 20 of the disc 12 and 21 of the frame 11, which are interconnected by the actual solder layer 22. The latter consists of an alloy product of lead with 2.5 percent by weight silver and is 0.05 to 1 mm thick. The layers 20 and 21 represent double layers which correspond to those which are denoted by 23 and 24 in FIG. The layer 23 consists of nickel and is approximately 200 nm thick. The layer 24 consists of a vapor deposition layer made of chromium and chromium oxide and is at least 30 nm strong.

The layers 20 and 21 can, however, also be constructed from three layers 25, 26 and 27 according to FIG. In this embodiment, they are evaporated onto the output window 12.1, which corresponds to the window 12 in FIG. 2, by first coating the layer 25, which consists of chromium or chromium oxides and is at least 30 nm thick, then the layer 26 of nickel, which is at least 30 nm thick, and finally the layer 27 consisting of silver and about 200 nm thick is evaporated.

In a quadruple layering of the adhesive layer according to FIG. 5, in which the pane of the exit window is denoted by 12.2, a layer 28 of chromium / chromium oxide is first vapor-deposited on the edge of the window slide 12.2 to be soldered by at least 30 nm. This is followed by an evaporation layer 29, which consists of nickel and is 100 nm to 300 nm thick. A subsequent layer 30 made of silver is then evaporated to a thickness of approximately 200 nm and finally a covering layer 31 consisting of gold.

Because of the use of soft solder, the disk 12 can be detached again from the piston 1 of the image intensifier. This is done by unsoldering from the frame 11. Then the pane 12 used as the substrate of the luminescent layer 13 can be easily recovered and reprocessed. This is a decisive advantage, especially when using fine optical panes, compared to soldering with glass solders, which can only be solved at temperatures above 600 ° C. While soft solder can be easily removed, a glass-soldered disc at the solder points always shows residues of glass solder after loosening the solder, which can only be removed by grinding.

Claims (10)

1. An X-ray image intensifier whose output window is set in a metal frame held in the tube bulb, characterised in that as an ouptut window a windowpane with phosphor applied to it is soldered in the frame by means of soft solder.

2. An X-ray image intensifier according to claim 1, characterised in that the solder is a lead alloy.

3. An X-ray image intensifier according to claim 2, characterised in that the lead alloy includes silver, tin or indium.

4. An X-ray image intensifier according to claim 3, characterised in that the silver amounts to 2.5 percent by weight.

5. An X-ray image intensifier according to claim 1, characterised in that the edge of the windowpane free of the phosphorescent substance has bonding layers at the points on which soldering takes place.

6. An X-ray image intensifier according to claim 5, characterised in that the bonding layers are applied in the form of a succession of layers whereof that applied to the glass is chromium oxide/chromium with a thickness of 30 to 300 nm, to this nickel is applied in a thickness of 30 to 300 nm and thereon silver is applied in a thickness of 100 to 400 nm.

7. An X-ray intensifier according to claim 5, characterised in that the bonding layers represent a succession of layers of which the layer applied to the glass comprises chromium/chromium oxide and is at least 30 nm thick, that applied to the chromium layer is a layer of iron, and thereon a layer of nickel and on this a layer of silver.

8. An X-ray image intensifier according to any one of claims 5 to 7, characterised in that the bonding layers are provided with a covering of gold.

9. An X-ray image intensifier according to any one of claims 5 to 8, characterised in that the soldering surface of the frame is also provided with bonding layers.

10. An X-ray image intensifier according to claim 9, characterised in that the top layer of the bonding layer of the frame and the top layer of the bonding layer of the windowpane comprise the same material.

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