EP1714298B1 - Modular x-ray tube and method for the production thereof - Google Patents

Abstract

Modular X-ray tube ( 10 ) and method for the production of such an X-ray tube, in which an anode ( 20 ) and a cathode ( 30 ) are arranged in a vacuumized inner space ( 40 ) situated opposite each other, electrons (e<SUP>-</SUP>) being produced at the cathode ( 30 ) and X-rays (y) at the anode ( 20 ). The X-ray tube ( 10 ) according to the invention comprises a multiplicity of acceleration modules ( 41, . . . , 45 ), complementing one another, and each acceleration module ( 41, . . . , 45 ) comprises at least one potential-carrying acceleration electrode ( 20/30/423/433/443 ). A first acceleration module ( 41 ) thereby comprises the cathode ( 30 ), a second acceleration module ( 45 ) the anode ( 20 ). The X-ray tube ( 10 ) further comprises at least one other acceleration module ( 42, . . . , 44 ). In particular, the X-ray tube according to the invention can possess a re-closeable vacuum valve, enabling individual defective parts of the tube ( 10 ) to be replaced in a simple manner or enabling the tube ( 10 ) to be modified in a modular way.

Description

The present invention relates to an X-ray tube for high dose rates, a corresponding method for generating high dose rates with X-ray tubes and a method for producing corresponding X-ray devices, in which an anode and a cathode in a vacuumized interior are arranged opposite to each other, wherein electrons by means of applying high voltage the anode will be accelerated.

The use of X-ray tubes is widely used in scientific and technical applications. X-ray tubes are found not only in medicine, e.g. in diagnostic systems or in therapeutic systems for irradiation of diseased tissue use, but they are e.g. also used for the sterilization of substances such as blood or food or for sterilization (infertility) of living things such as insects. Other applications are further found in traditional x-ray technology, such as e.g. the scanning of luggage and / or transport containers or the non-destructive inspection of workpieces, e.g. Concrete reinforcements, etc. Various methods and devices for X-ray tubes are described in the prior art. These range from miniaturized tubes in the form of a transistor package, to high-performance tubes with an acceleration voltage of up to 450 kilovolts. Particularly recently, much effort and effort has been made by industry and technology to improve the performance and / or efficiency and / or life and / or maintenance capabilities of irradiation systems. These efforts have been made particularly by new requirements in safety systems, such as e.g. when scanning large cargo containers in air traffic, etc., and similar devices triggered.

Conventional X-ray tube types used in industrial environments consist of either glass or metal-ceramic composites. FIG. 1 shows schematically an example of such a conventional X-ray tube from a glass composite. FIG. 2 and 3 show conventional x-ray tubes made of metal-ceramic composites. In the X-ray tubes, electrons pass through an electric field in a vacuumized tube. They are thereby accelerated to their final energy and convert them to a target surface in X-radiation. That is to say, x-ray tubes comprise an anode and a cathode, which are arranged opposite one another in a vacuumized interior, and which in the metal-ceramic tubes are arranged opposite a cylindrical metal part (FIG. Figure 2/3 ) and glass tubes of a glass cylinder ( FIG. 1 ) are enclosed. In glass tubes, the glass acts as an insulator. In the case of the metal-ceramic tubes, on the other hand, the anode and / or cathode are usually electrically insulated by means of a ceramic insulator, the ceramic insulator (s) being arranged axially to the metal cylinder behind the anode and / or cathode and closing the vacuum space at the respective end. The ceramic insulators are typically disk-shaped (annular) or conical. In principle, any type of insulator geometry would be possible with this type of tube, with field peaks being taken into account at high voltages. In general, the ceramic insulators have in their middle an opening in which a high voltage supply to the anode or the cathode, are used vacuum-tight. These types of x-ray tubes are also referred to in the art as bipolar or bipolar x-ray tubes ( FIG. 3 ). Of these, so-called unipolar devices ( FIG. 2 ), in which the anode, ie the target, is set to ground potential. In the bipolar systems, the electron source (cathode) is set to a negative high voltage (HV) and the target (anode) is set to a positive high voltage. In all designs of the prior art, however, is the full acceleration voltage for the acceleration of electrons (one-stage) between the anode and the cathode. It should also be noted that there are solutions in which an earthed (diaphragm) between the anode and cathode is mounted. This intermediate diaphragm can serve on the one hand as an electron-optical lens, but also as a mechanical diaphragm for electrons backscattered by the target.

The problems and disadvantages of this one-step construction are that with increasing applied voltages, the probability of disturbing physical effects also increases. These currently limit the prior art X-ray tubes to unipolar ones Tubes to a maximum of about 200 to 300 kV and in bipolar devices to a maximum of about 450 kV voltage applied. As just mentioned, it is the additional physical effects, such as field emission, secondary electron emission, and photoelectric effect, that occur in addition to the desired generation of X-rays during operation of an X-ray tube that limit the performance of the tube. However, these effects not only disturb the function of the X-ray tube, but can lead to a deterioration of the material and thus to premature fatigue of the parts. In particular, the secondary electron emission is known for the impairment of the X-ray tube operation. In the case of secondary electron emission, when the electron beam impinges on the anode, in addition to the X-rays, undesired but unavoidable secondary electrons propagate in the interior of the X-ray tube on tracks corresponding to the field lines. These secondary electrons can reach the insulator surface through various scattering and impact processes and there reduce the HV insulation properties. However, secondary electrons also result from the fact that the insulators are hit at the anode and / or cathode during operation of unavoidable field emission electrons and trigger secondary electrons there. The electric field is generated when the high voltage is switched on at the anode and cathode, ie: during operation of the x-ray tube, in the interior and the interior facing surfaces. This also includes the surfaces of the insulator. The shorter the X-ray tube is and the wider the ceramic insulator, the greater the likelihood that secondary and / or field emission electrons impact the ceramic part (s). As a result, the high-voltage strength and life of the device are undesirably lowered. In disc-shaped insulators, it is therefore from the prior art, for example DE2855905 known to use so-called shielding electrodes. The shielding electrodes can be used, for example, in pairs, wherein they are usually arranged coaxially at a certain distance in a rotationally symmetrical shape of the x-ray tube in order to optimally prevent the propagation of the secondary electrons. As has been shown, however, such devices can no longer be used at very high voltage. In addition, the material and manufacturing costs in such structures is greater than in X-ray tubes with only insulators. Another possibility of the prior art is eg in DE6946926 shown. In order to reduce the attack surface, a conical ceramic insulator is used in these solutions. The ceramic insulator has a substantially constant wall thickness and is coated, for example, with a vulcanized rubber layer. The layer should contribute to the fact that secondary electrons occur less strongly. As mentioned, the electric field inside the vacuum space also senses the surfaces of the insulators. Particularly in the case of conical insulators, the field accelerates an electron impinging on the insulators or a scattered electron triggered by an impinging electron away from the surface in the direction of the anode. In principle, the insulation cones are shaped such that the normal vector of the electric field accelerates the electrons away from the insulator surface. If the anode-side insulator, like the cathode-side insulator, is designed as a truncated cone protruding into the interior, then an electron impinging on the insulator (for example an electron triggered from the metal piston) is likewise accelerated towards the anode. For example, the anode-side cone of the insulator is shaped so that the normal vector faces away from the surface. On the anode side, the electron moves along the insulator surface, because no electric field acting on the insulator surface acts on the electron. After passing through a certain distance such an electron has enough energy to trigger more electrons, which in turn trigger electrons, so that it comes to a running on the insulator surface to the anode electron avalanche, the significant disruption, possibly even gas eruptions or even a breakdown of the insulator can cause. The higher the voltage, the more significant this effect becomes. At very high voltages, this type of insulators can therefore no longer be used. It should also be noted that the geometric length increases with increasing applied electric field. Depending on the energy and the exit angle, electrons can also run in the direction of the cathode, in particular with scattered electrons. However, the effect described above is less pronounced on the cathode side because electrons that reach the insulator surface on the cathode side or are triggered by the vacuum move towards the metal cylinder and do not move along the insulator surface. To avoid the disadvantage, various solutions are known in the prior art, for example, in the published patent application DE2506841 proposed on the cathode side, the insulator such that between the insulator and the tube a conical Cavity arises. Another solution of the prior art, for example, in the patent EP0215034 shown where the disc-shaped insulator is stepped stepped against the metal cylinder. It has been found, however, that all the solutions shown in the prior art at high voltages, ie, for example, above 150 kV, have disturbances which, inter alia, lead to premature aging of the material and can produce gas eruptions and / or breakthroughs of the insulator. Thus, the X-ray tubes known in the art are poorly or not at all usable for many modern applications with very high voltages (> 400 kV).

It is an object of this invention to propose a novel X-ray tube and a corresponding method for producing such an X-ray tube, which does not have the disadvantages described above. In particular, an X-ray source is to be proposed which allows several times higher electrical powers than conventional X-ray sources. Likewise, the tubes should be built modular and easy and inexpensive to manufacture. Further, any defective parts of the X-ray tube should be interchangeable without having to replace the whole X-ray tube.

According to the present invention, this object is achieved in particular by the elements of the independent claims. Further advantageous embodiments are also evident from the dependent claims and the description.

In particular, these objects are achieved by the invention in that in an X-ray tube, an anode and a cathode are arranged opposite each other in a vacuumized interior, wherein at the cathode electrons are generated, are accelerated by means of applying high voltage to the anode and X-rays at the anode means wherein the x-ray tube comprises a plurality of complementary acceleration modules, the acceleration modules each comprising at least one potential-carrying electrode, wherein the first acceleration module comprises the cathode with primary electron generation and the last acceleration module comprises the anode with the x-ray generation, and wherein the x-ray tube at least one further acceleration module comprising a potential-carrying electrode, which acceleration module for the acceleration of electrons is repeatedly reproducible in series switchable, and wherein the x-ray tube is modular buildable. The anode may comprise a target for X-ray generation with an exit window or be formed as a transmission anode, which closes the vacuumized interior of the X-ray tube to the outside. At least one of the electrodes may include spherically shaped ends for reducing or minimizing the field enhancement at the respective electrode. The electrodes can be connected, for example, by means of potential connections, for example, to a high-voltage cascade. One advantage of the invention is, inter alia, that very high power X-ray radiation can be generated, with the geometrical size of the X-ray tube being small, especially with tubes of the prior art. At the same time, the invention enables an X-ray tube which is stably operable over a very wide electric potential range without changing performance characteristics. Another advantage of the invention is, inter alia, a much lower load on the insulator by the E field. This is especially true in comparison to the conventional disk insulators. The inventive X-ray tube can be produced, for example, in a single-stage vacuum brazing process. This has the particular advantage that the subsequent evacuation of the X-ray tube can be omitted by means of high vacuum pumps. It is a further advantage that the X-ray tubes according to the invention are particularly suitable for the one-shot method due to their simple and modular construction, since the fields inside the tube are much smaller than in conventional tubes and the tube according to the invention is therefore less susceptible to contamination and / or leaks.

In one embodiment variant, the potential difference between each two potential-carrying electrodes of adjacent acceleration modules is chosen to be constant for all acceleration modules, the final energy of the accelerating electrons being an integer multiple of the energy of an acceleration module. This variant has the advantage, inter alia, that the load on the insulators over the distance is constant and no field increases occur, which can adversely affect the operability of the tube.

In another embodiment variant, at least one of the acceleration modules has a resealable vacuum valve. The acceleration modules can be provided on one or both sides with a vacuum seal to allow an air-tight closure between the individual acceleration modules. This variant has u.a. the advantage that by means of the vacuum valve, individual parts of the X-ray tube can be replaced without, as in conventional X-ray tubes, the same whole tube must be replaced. Since the tube has a modular design, the tube can also be subsequently easily adapted to changing operating conditions by using additional acceleration modules or removing existing modules. This is not possible with any of the prior art tubes.

In a further embodiment, the acceleration modules comprise a cylindrical insulating ceramic. This variant has u.a. the advantage that the mechanical design effort at moderate load through the electric field is low, exceptionally high performance characteristics can be achieved.

In yet another embodiment variant, the insulation ceramic has a high-resistance inner coating. This variant has u.a. the advantage that disturbing charges by scattered electrons, caused on the one hand by field-related processes in the insulator material, on the other hand by the backscattered by the anode target secondary electrons and by field emission electrons, is avoided. Thus, the life of the X-ray tubes and / or the potential differences between the individual acceleration electrodes can be additionally increased.

In one embodiment, the insulation ceramic 53 comprises a rib-shaped outer structure. Due to the shape of the insulation ceramic 53, the insulation distance on the outside (atmosphere side) of the insulator can be extended. This variant has the advantage, among other things, that it has a high-voltage correspondingly shaped external structure. This exterior structure additionally allows for improved efficient cooling of the x-ray tube.

In one embodiment, the electrodes of the acceleration modules comprise a shield for suppressing the scattered electron flow to the insulating ceramic. At least one of the shields may include spherically shaped ends for reducing or minimizing field elevation at the respective shield. This variant has u.a. the advantage that the shields provide additional protection for the insulation ceramics. Thus, the life of the X-ray tubes and / or the potential differences between the individual acceleration electrodes can be additionally increased.

In one embodiment variant, the x-ray tube according to the invention is produced by the one-shot method. This has u.a. the advantage that the subsequent evacuation of the X-ray tube 10 can be omitted by means of high vacuum pumps. Another advantage of the one-shot method, i. The one-step manufacturing process by the total soldering of the tube in vacuum (one-shot method), among other things, that one has a single manufacturing process and not as conventional three: 1. assemblies soldering / assembly assemble 2. (eg soldering or welding) / 3. Evacuate tube by means of vacuum pump. The one-step manufacturing process is therefore more economically efficient, time-saving and cheaper. At the same time, contamination of the tube can be minimized in this process with suitable process control. Nevertheless, it may be advantageous if the tube is already largely free of impurities, which minimizes the dielectric strength of the insulating ceramics in the rule. Vacuum tightness requirements for the tubes 10 are the same in most cases in the one-shot process as in multi-stage manufacturing processes.

It should be noted at this point that the present invention relates not only to the method according to the invention but also to a device for carrying out this method and to a method for producing such a device. In particular, it also relates to irradiation systems which comprise at least one X-ray tube according to the invention with one or more high-voltage cascades for supplying voltage to the at least one X-ray tube.

• Figur 1 zeigt ein Blockdiagramm, welches schematisch eine Röntgenröhre 10 aus einem Glasverbund des Standes der Technik zeigt. Dabei werden Elektronen e^- von einer Kathode 30 emittiert und Röntgenstrahlen γ von einer Anode 20 durch ein Fenster 201 abgestrahlt. 50 ist ein zylindrische Glasröhre, wobei das Glas als Isolator dient.
• Figur 2 zeigt ein Blockdiagramm, welches schematisch eine unipolare Röntgenröhre 10 aus einem Metall-Keramik-Verbund des Standes der Technik zeigt. 51 ist der Keramik-Isolator, 52 der auf Erde gesetzte Metallzylinder. Dabei werden Elektronen e^- von einer Kathode 30 emittiert und Röntgenstrahlen γ von einer Anode 20 durch ein Fenster 201 abgestrahlt.
• Figur 3 zeigt ein Blockdiagramm, welches schematisch eine bipolare Röntgenröhre 10 ebenfalls aus einem Metall-Keramik-Verbund des Standes der Technik zeigt. 51 ist der Keramik-Isolator, 52 der auf Erde gesetzte Metallzylinder. Dabei werden Elektronen e^- von einer Kathode 30 emittiert und Röntgenstrahlen γ von einer Anode 20 durch ein Fenster 201 abgestrahlt.
• Figur 4 zeigt ein Blockdiagramm, welches schematisch ein Beispiel einer Aussenansicht einer erfindungsgemässen Röntgenröhre 10 zeigt.
• Figur 5 zeigt ein Blockdiagramm, welches schematisch die Architektur einer Ausführungsvariante einer erfindungsgemässen Röntgenröhre 10 zeigt. Dabei werden Elektronen e^- von einer Kathode 30 emittiert und Röntgenstrahlen γ von einer Anode 20 abgestrahlt. Die Röntgenröhre 10 umfasst mehrere einander ergänzende Beschleunigungsmodule 41,...,45 und jedes Beschleunigungsmodul 41,...,45 umfasst mindestens eine potentialtragende Elektrode 20/30/423/433/443.
• Figur 6 zeigt ein Blockdiagramm, welches schematisch die Architektur einer weiteren Ausführungsvariante einer erfindungsgemässen Röntgenröhre 10 zeigt. Die Röntgenröhre 10 umfasst wie in Figur 3 mehrere einander ergänzende Beschleunigungsmodule 41,...,45 mit potentialtragenden Elektroden 20/30/423/433/443. Die Beschleunigungsmodule umfassen zusätzlich Elektronenabschirmungen 422/432/442 zur Unterdrückung des Streuelektronenflusses auf die Isolationskeramik.
• Figur 7 zeigt ebenfalls ein Blockdiagramm, welches schematisch die Architektur einer anderen Ausführungsvariante einer erfindungsgemässen Röntgenröhre 10 zeigt. Die Röntgenröhre 10 umfasst wie in Figur 3 mehrere einander ergänzende Beschleunigungsmodule 41,...,45 mit potentialtragenden Elektroden 20/30/423/433/443. Mindestens eines der Beschleunigungsmodule 41,...,45 umfasst zusätzlich ein wiederverschliessbares Vakuumventil 531.
• Figur 8 zeigt eine Querschnittansicht einer erfindungsgemässen Röntgenröhre 10, welche schematisch die Architektur einer Ausführungsvariante gemäss Figur 3 zeigt.
• Figur 9 zeigt eine weitere Querschnittansicht einer erfindungsgemässen Röntgenröhre 10. Die Beschleunigungsmodule 41,...,45 umfassen zusätzlich eine mögliche Ausführungsform von Abschirmungen 423...443 zur Unterdrückung des Streuelektronenflusses auf die Isolationskeramik. Diese Ausführungsvariante hat u.a. den Vorteil, dass die Abschirmungen einen zusätzlichen Schutz für die Isolationskeramiken bilden. Damit kann die Lebensdauer der Röntgenröhren und/oder die Potentialdifferenzen zwischen den einzelnen Beschleunigungselektroden zusätzlich erhöht werden. Die mögliche Ausführungsform von Figur 9 zeigt kugelförmig bzw. konusförmig ausgebildete Enden der Elektroden 423/433/443 und/oder der Abschirmungen 412,...,415 zur Herabsetzung oder Minimierung der Feldüberhöhung an der jeweiligen Elektrode 423/433/443 und/oder Abschirmung 412,...,415. Die Elektroden 423/433/443 sind durch die Potentialanschlüsse z.B. an eine Hochspannungskaskade anschliessbar.
• Figur 10 zeigt den prinzipiellen Aufbau einer Beschleunigungsstufe einer modularen Metall-Keramik-Röhre mit einer modularen zweistufigen Beschleunigungsstufe mit zwei Beschleunigungsmodulen 42/43 mit Isolationskeramik 50, Beschleunigungselektroden 423/433 und Potentialanschlüssen 421/431.
• Figur 11 zeigt schematisch die Potentialverteilung in einer erfindungsgemässen modularen Röntgenröhre 10 eines Ausführungsbeispiels mit einer 800kV-Röhre.
• Figur 12 zeigt schematisch ein Bestrahlungssystem 60 mit einer erfindungsgemässen Röntgenröhre 10. Das Bestrahlungssystem 60 umfasst eine Hochspannungskaskade 62 zur Spannungsversorgung der Röntgenröhre 10, ein Hochspannungstransformer 63 sowie ein Austrittsfenster 61 für die Röntgenstrahlung γ aus dem Abschirmungsgehäuse 65.
• Figur 13 zeigt eine weitere Ausführungsvariante dreier Beschleunigungsmodulen 42/43/44 mit Isolationskeramik 50, Elektronenabschirmung 422/432/442 und Beschleunigungselektroden 423/433/443.

Hereinafter, embodiments of the present invention will be described by way of examples. The examples of the embodiments are illustrated by the following enclosed figures:

• FIG. 1 FIG. 12 is a block diagram schematically showing an X-ray tube 10 of a prior art glass composite. In this case, electrons e ^{- are} emitted from a cathode 30 and x-rays γ are emitted from an anode 20 through a window 201. 50 is a cylindrical glass tube with the glass serving as insulator.
• FIG. 2 Fig. 12 is a block diagram schematically showing a prior art unipolar X-ray tube 10 made of a metal-ceramic composite. 51 is the ceramic insulator, 52 is the metal cylinder set on earth. In this case, electrons e ^{- are} emitted from a cathode 30 and x-rays γ are emitted from an anode 20 through a window 201.
• FIG. 3 shows a block diagram which schematically shows a bipolar X-ray tube 10 also of a metal-ceramic composite of the prior art. 51 is the ceramic insulator, 52 is the metal cylinder set on earth. In this case, electrons e ^{- are} emitted from a cathode 30 and x-rays γ are emitted from an anode 20 through a window 201.
• FIG. 4 shows a block diagram which schematically shows an example of an external view of an inventive X-ray tube 10.
• FIG. 5 shows a block diagram, which schematically shows the architecture of an embodiment of an inventive X-ray tube 10. In this case, electrons e ^{- are} emitted by a cathode 30 and x-rays γ are emitted by an anode 20. The X-ray tube 10 comprises a plurality of complementary acceleration modules 41, ..., 45 and each acceleration module 41, ..., 45 comprises at least one potential-carrying electrode 20/30/423/433/443.
• FIG. 6 shows a block diagram, which schematically shows the architecture of another embodiment of an inventive X-ray tube 10 shows. The X-ray tube 10 comprises as in FIG FIG. 3 a plurality of complementary acceleration modules 41, ..., 45 with potential-carrying electrodes 20/30/423/433/443. The acceleration modules additionally include electron shields 422/432/442 for suppressing the stray electron flux to the insulating ceramic.
• FIG. 7 also shows a block diagram, which schematically shows the architecture of another embodiment of an inventive X-ray tube 10. The X-ray tube 10 comprises as in FIG FIG. 3 a plurality of complementary acceleration modules 41, ..., 45 with potential-carrying electrodes 20/30/423/433/443. At least one of the acceleration modules 41,..., 45 additionally comprises a resealable vacuum valve 531.
• FIG. 8 shows a cross-sectional view of an inventive X-ray tube 10, which schematically shows the architecture of an embodiment according to FIG. 3 shows.
• FIG. 9 shows a further cross-sectional view of an inventive X-ray tube 10. The acceleration modules 41, ..., 45 additionally include a possible embodiment of shields 423 ... 443 for suppressing the stray electron flow to the insulating ceramic. This embodiment variant has the advantage, inter alia, that the shields form an additional protection for the insulation ceramics. Thus, the life of the X-ray tubes and / or the potential differences between the individual acceleration electrodes can be additionally increased. The possible embodiment of FIG. 9 shows spherically shaped ends of the electrodes 423/433/443 and / or the shields 412, ..., 415 for reducing or minimizing the field elevation at the respective electrode 423/433/443 and / or shield 412, ... , 415th The electrodes 423/433/443 can be connected through the potential connections, for example, to a high-voltage cascade.
• FIG. 10 shows the basic structure of an acceleration stage of a modular metal-ceramic tube with a modular two-stage acceleration stage with two acceleration modules 42/43 with insulating ceramic 50, acceleration electrodes 423/433 and potential terminals 421/431.
• FIG. 11 schematically shows the potential distribution in an inventive modular X-ray tube 10 of an embodiment with an 800kV tube.
• FIG. 12 schematically shows an irradiation system 60 with an inventive X-ray tube 10. The irradiation system 60 includes a high voltage cascade 62 for powering the X-ray tube 10, a high voltage transformer 63 and an exit window 61 for the X-ray γ from the shield case 65th
• FIG. 13 shows a further embodiment of three acceleration modules 42/43/44 with insulation ceramic 50, electron shield 422/432/442 and acceleration electrodes 423/433/443.

FIGS. 4 to 10 illustrate architectures that can be used to implement the invention. In these embodiments for a modular x-ray tube 10, an anode 20 and a cathode 30 are placed in a vacuumized interior 40 opposite one another. The electrons e ^- are generated at the cathode 30, wherein the cathode 30 serves as an electron emitter. The cathode 30 thus serves on the one hand for generating the electric field E, on the other hand also for electron generation. Therefore, all materials are in principle suitable for this application, the electrons e ^- can emit. This process can be achieved by thermal emission, but also by field emission (cold emitter). As a cold emitter, for example, any type of microtiparrays with mostly diamond-like structures or, for example, also nanotubes can be used. Of course, the cold emission in this tube type can also be exploited by utilizing the Penning effect on suitably shaped metals. For example, it is possible to use thermal emitters which can also be used in this emitter concept, for example tungsten (W), lanthanum hexaboride (LaB ₆ ), dispenser cathodes (La in W) and / or oxide cathodes (for example ZrO). The electrons e ^- are accelerated by means of applying high voltage to the anode 20 and generate x-rays γ On an object surface of the anode 20. The anodes 20 perform two functions in the X-ray tubes 10. First, they serve as a positive electrode 20 for generating an electric field E for accelerating the electrons e ^- . On the other hand, the anodes 20 or the target material embedded in the anodes 20 serve as a location where the electron energy is converted into X-radiation γ. This conversion depends on the one hand on the particle energy, but also on the atomic number of the target material. Firstly, according to the Bethe formula, the energy loss of the particles is quadratic with the atomic number Z of the target material $${{}^{\mathit{dW}}\mathit{/}}_{\mathit{dx}}\approx Z^2$$

In this process, the anode 20 is thermally stressed. The anode or the target material must therefore be able to survive this thermal stress. It follows that the vapor pressure of the target material at the operating temperature of the target should be sufficiently small so as not to negatively influence the vacuum necessary for the operation of the X-ray tube 10. Therefore, for example, target materials can be preferably used which are resistant to high temperatures or can be cooled well. For this purpose, the target material, for example, be embedded in a good heat conductive material (eg copper), which can be well cooled ie good thermal conductivity. For example, it is therefore possible to use as heavy and temperature-resistant materials as the anode (target) 20. In particular, materials such as tungsten (W, Z = 74) and / or uranium (U, Z = 92) and / or rhodium (Rh, Z = 45) and / or silver (Ag, Z = 47) and / or or molybdenum (Mo, Z = 42) and / or palladium (Pd, Z = 46) and / or iron (Fe, Z = 26) and / or copper (Cu, Z = 29). In the selection of the target material, it may be particularly advantageous, for example in analytical applications, to take into account that the characteristic lines (K _α ) are suitable for the specific application.

The x-ray tube 10 further comprises a plurality of complementary acceleration modules 41, ..., 45. Each acceleration module 41,..., 45 comprises at least one potential-carrying electrode 20/30/423/433/443 with the corresponding potential connections 421/431/441. A first acceleration module 41 comprises the cathode 30 with the electron production e ^- , ie with the electron emitter. A second acceleration module 45 comprises the anode 20 with the X-radiation γ. The x-ray tube comprises at least one further acceleration module 42,..., 44 with a potential-carrying electrode 423/433/443. The vacuumized interior 40 may be closed, for example, by means of insulating ceramic 51 to the outside. For the emitter concept according to the invention, it is possible, for example, to use insulation materials which satisfy the electrical requirements of the x-ray tube 10 (field strength). For corresponding embodiments, the insulating materials should also be suitable for producing a metal-ceramic connection. In addition, the ceramic should be applicable for Hochvaku umanwendungen. Suitable materials are thus, for example, pure oxide ceramics, such as aluminum, magnesium, beryllium and zirconium oxide. Also monocrystalline Al ₂ O ₃ (sapphire) is suitable in principle. Furthermore, so-called glass ceramics, such as Macor, or similar materials are conceivable. In particular, mixed ceramics (eg doped Al ₂ O ₃ ) are of course suitable if they have the appropriate properties. The insulation ceramics 51 may be designed, for example, outward in rib shape or the like, in order to extend insulating distance of the insulation jacket 51, which is not vacuum-side, that is, for example, is located in insulating oil. In the same way, however, any other embodiment, for example, a pure cylindrical shape, the insulating ceramic 51 conceivable without the core of the invention would be affected. In addition, the insulation ceramic 51 may, for example, also have a high-resistance inner coating in order to dissipate possible charges that can be caused by various electronic processes, at the same time ensuring that the acceleration voltage can be applied. FIG. 8 shows the basic structure of a modular metal-ceramic tube of two such further acceleration modules 42/43 with insulation ceramic 51, acceleration electrodes 423/433 and potential terminals 421/431. Are used (multi-step acceleration) ^- The principle described here for the construction of X-ray tubes 10, which for example consists of a metal-ceramic composite can according to the invention are switched as often repeatable in series and so to accelerate electrons e. The last potential-carrying electrode of the acceleration structure is the anode 20 required for the production. On the other hand, the cathode 30 necessary for electron generation constitutes the first electrode of the acceleration structure This is in the embodiments of the FIGS. 4 to 9 shown. With a suitable arrangement and choice of electrodes X-ray tubes 10 can be built with a total energy up to 800 kilovolts or more (eg FIG. 5 ). By contrast, conventional X-ray tubes have been produced with a maximum total energy of 200 to 450 kilovolts. An essential advantage of this concept is that it achieves very high energies with small designs at the same time. Another advantage over existing concepts is the almost homogeneous loading of the segments of the insulating ceramics 51 by the electric field. This has the advantage, inter alia, that the X-ray tube 10 can be configured by segmentation so that the field-moderate loading of the insulating ceramics 51 remains below a limit value necessary for high-voltage flashovers. FIG. 9 schematically shows the potential distribution in an inventive modular X-ray tube 10 of an embodiment with an 800kV tube. On the other hand, in the case of the X-ray tubes used in the prior art, there is a strong radial stress on the insulating ceramics because the tubes are constructed substantially similar to a cylindrical capacitor. These radial fields lead to very high field strengths at the interface between the insulator inner radius and the axially arranged acceleration electrodes (anode, cathode). This enormous field elevation at the so-called triple point (insulator-electrode-vacuum) leads to field emissions of electrons, which generate high-voltage flashovers and can lead to the destruction of the tube, as already described above. FIG. 1 Fig. 12 schematically shows an architecture of such a conventional X-ray tube 10 of the prior art. In this case, electrons e- from an electron emitter, that is a cathode 20, usually a hot tungsten filament, emitted accelerated by an applied high voltage to a target, wherein X-rays γ from the target, ie the anode 30 is emitted through a window 301. Triple points (field increases the to field emission of electrons e ^- lead) incurred while both the cathode side and the anode side.

The potential difference between in each case two potential-carrying electrodes 20/30/423/433/443 of adjacent acceleration modules 41,..., 45 may, for example, also be constant for all acceleration modules 41,. wherein the final energy of the accelerated electrons e ^{- is} an integer multiple of the energy of an acceleration module 41, ..., 45. At least one of the acceleration modules 41,..., 45 may further comprise a resealable vacuum valve 531. This has the advantage that by means of the vacuum valve 531 individual parts of the X-ray tube 10 can be replaced without, as in conventional X-ray tubes, the same whole tube must be replaced. Since the tube 10 according to the invention has a modular design, the tube 10 can subsequently also be easily adapted to changed operating conditions by using further acceleration modules or by removing existing modules. This is not possible with any of the prior art tubes.

It is important to point out that in the inventive X-ray tubes 10 is a principal modularity, ie the increase of the beam energy of X-ray tubes 10 can be achieved by adding one or more acceleration segments 41, ..., 45 or acceleration modules 41, ..., 45 , In this case, at least one of the acceleration modules 41,..., 45 can be designed such that it carries a resealable vacuum valve 531. The acceleration modules 41,..., 45 could additionally comprise vacuum seals on one or both sides. This has the advantage that individual defective acceleration modules 41,..., 45 can be easily replaced and / or recycled by un-vacuuming a defective tube 10 by means of the resealable vacuum valve 531, through the defective acceleration module 41, new and / or working is replaced and the tube 10 is re-vacuumed with a corresponding vacuum pump via the resealable vacuum valve 531. It is also important to point out that the electrodes 20/30/423/433/443 of the acceleration modules 41,..., 45 can comprise a shield 412,..., 415 for suppressing the scattered electron flow to the insulating ceramic 51 ( Figure 6/13 ). This has the advantage that the shields form an additional protection for the insulating ceramics 51. Thus, the life of the X-ray tubes and / or the potential differences between the individual acceleration electrodes 20/30/423/433/443 can be additionally increased. The simple and modular construction of the x-ray tube 10 according to the invention is particularly suitable for production processes in the one-shot method, or this construction allows the one-shot process only efficiently. The soldering of the entire tube 10 takes place in a single-stage vacuum brazing process. This has the advantage, inter alia, that the subsequent evacuation of the x-ray tube 10 by means of high-vacuum pumps can be dispensed with. Another advantage of the one-shot process, ie the one-step production process by the total soldering of the tube in vacuum (one-shot method), is, among other things, that one has a single manufacturing process and not three as usual: 2. Assemble assemblies (eg soldering or welding) / 3. Evacuate tube by means of vacuum pump. The one-step manufacturing process is therefore more economically efficient, time-saving and cheaper. At the same time, with proper process control, the contamination of the tube can be minimized. Nevertheless, it may be advantageous if the tube is already largely free of impurities, which minimizes the dielectric strength of the insulating ceramics in the rule. Vacuum tightness requirements for the tubes 10 are the same in most cases in the one-shot process as in multi-stage manufacturing processes. In addition, since the fields within the tube 10 are much smaller than conventional tubes, the inventive tube 10 is less susceptible to contamination and / or leaks. This makes the X-ray tube 10 according to the invention more suitable for the one-shot method. For example, the X-ray tube 10 according to the invention can also be used excellently for producing entire radiation systems and / or individual radiation devices 60 (see FIG. 12 ). In such a radiation device 60, the tube 10 may be mounted in a housing 65, for example, in insulating oil. The shielding housing 65 may include an exit window 61 for X-radiation γ. The radiation device 60 comprises for the tube 10 a corresponding high-voltage cascade 62, for example with an associated high-voltage transformer 63 and voltage terminals 64 to the outside. Such radiation devices 60 or monobloc 60 can then be used, for example, to produce larger radiation systems. Of course, it is clear to those skilled in the art that the inventive tube 10 without a target or transmission anode is also outstandingly suitable as an electron emitter and / or electron gun with the corresponding industrial fields of application due to its simple, modular construction and its high powers.

It may be useful for the embodiment according to the invention that the shields 422/432/442 are shaped so that the electron beam does not "see" an insulator surface 51 (FIG. FIG. 13 ). By applying the acceleration voltage, charging effects of the ceramic insulators 51 may occur, which need not necessarily be caused by scattered and secondary electron emission. By a in FIG. 13 illustrated geometry or a similar geometry, such charging effects can be prevented or minimized. A coating of the insulation ceramic can also be used, in particular, to supply the potential if, for example, a suitable conductive layer is attached to the outside of the insulators, so that the layer acts as a voltage divider. A suitable coating could also replace the metallic electrodes 423/433/443 against the vacuumized interior. However, this would mean that you no longer have shielding as in FIG. 13 Has. As an exemplary embodiment, it would be possible, for example, to attach a helical layer on the inside (vacuum) of the insulating ceramic 51, which acts as a voltage divider and thus replaces the sequence of metallic electrodes 423/433/443.

Claims (12)

1. An X-ray tube (10) in which an anode (20) and a cathode (30) are disposed opposite each other in a vacuumized inner space (40), electrons (e^-) being able to be produced at the cathode (30), being able to be accelerated to the anode (20) by means of impressible high voltage, and X rays (γ) being able to be produced at the anode (20) by means of the electrons (e^-), the X-ray tube (10) comprising a multiplicity of mutually complementary acceleration modules (41,...,45), each acceleration module (41,...,45) comprising at least one potential-carrying electrode (20/30/423/433/443), a first acceleration module (41) comprising the cathode (30) with electron extraction (e^-), and a second acceleration module (45) comprising the anode (20) with the X ray generation (γ),
   wherein
   the X-ray tube (10) comprises at least one further acceleration module (42,...,44) with a potential-carrying electrode (423/433/443), the acceleration module (42,...,44) for acceleration of electrons (e^-) being repeatedly connectible in series as often as desired, and the X-ray tube (10) being of modular construction.
2. The X-ray tube (10) according to claim 1, wherein the difference in potential between each two potential-carrying electrodes (20/30/423/433/443) of adjacent acceleration modules (41,...,45) is constant for all acceleration modules (41,...,45), the final energy of the accelerated electrons (e^-) being a whole-number multiple of the energy of an acceleration module (41,...,45).
3. The X-ray tube (10) according to one of the claims 1 or 2, wherein at least one of the acceleration modules (41,...,45) has a reclosable vacuum valve (531) and/or vacuum seals on one side or on two sides.
4. The X-ray tube (10) according to one of the claims 1 to 3, wherein the acceleration modules (41,...,45) include a cylindrical ceramic insulator (53).
5. The X-ray tube (10) according to claim 4, wherein the insulating ceramic (53) has a high-ohmic interior coating.
6. The X-ray tube (10) according to one of the claims 4 or 5, wherein the ceramic insulator (53) comprises a ridged exterior structure.
7. The X-ray tube (10) according to one of the claims 1 to 6, wherein the anode (20) comprises a target for X-ray generation as well as an emission hole (201) for X-radiation.
8. The X-ray tube (10) according to one of the claims 1 to 6, wherein the anode (20) includes a transmission anode, the transmission anode closing off the vacuumized inner space (40) toward the outside.
9. The X-ray tube (10) according to one of the claims 1 to 7, wherein the electrodes (20/30/423/433/443) of the acceleration modules (41,...,45) include a shield (412,...,415) for suppression of the stray electron flow on the ceramic insulator (51).
10. The X-ray tube (10) according to claim 9, wherein at least one of the electrodes (423/433/443 ) and/or shields (412,...,415) comprises spherically or conically designed ends for reducing or minimizing the field peak at the respective electrode (423/433/443) and/or shield (412,...,415).
11. An irradiation system (60), wherein the irradiation system (60) comprises at least one X-ray tube (10) according to one of the claims 1 to 10 with a high voltage cascade (62) for voltage supply of the X-ray tube (10).
12. A method of production of an X-ray tube (10) according to one of the claims 1 to 10, wherein the X-ray tube (10) is produced in a one-step vacuum soldering process.

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