Abstract
An x-ray anode for generating x-radiation includes a carrier body and a first emission layer and at least one second emission layer, which generate x-radiation when they are impinged by electrons. The emission layers are separated by an intermediate layer on one side of the carrier body and are arranged a distance apart in a central direction of the x-ray anode.
Claims
1. An x-ray anode for generating x-radiation, the x-ray anode comprising: a carrier body; a first emission layer arranged on an outer surface of the x-ray anode, and at least one second emission layer hidden in an interior of said carrier body, said first emission layer and said second emission layer both configured to generate x-radiation upon being impinged by electrons, said first emission layer and said second emission layer arranged on one side of said carrier body; and an intermediate layer disposed to separate said first and second emission layers from one another, and said first and second emission layers being disposed at a spacing distance from one another in a central direction of the x-ray anode; said spacing distance between said first and second emission layers in the central direction is at least 0.5 mm such that said first emission layer is used for generating x-radiation by interacting with high-energy electrons and said second emission layer is protected from the impingement of electrons by the intermediate layer and is therefore inactive.
2. The x-ray anode according to claim 1, wherein said first emission layer and said at least one second emission layer are congruent in a viewing direction along the central direction in a region of impingement of the electrons.
3. The x-ray anode according to claim 1, wherein, at least in certain portions, the spacing distance between said first emission layer and said second emission layer is substantially constant.
4. The x-ray anode according to claim 1, wherein at least one of said first emission layer and said second emission layer is formed of a material selected from the group consisting of tungsten, rhenium and a tungsten alloy.
5. The x-ray anode according to claim 4, wherein at least one of said first emission layer and said second emission layer is formed of a tungsten-rhenium alloy.
6. The x-ray anode according to claim 1, wherein said first emission layer and said at least one second emission layer are formed of a common material.
7. The x-ray anode according to claim 1, wherein said intermediate layer between said first and second emission layers is formed of a same material as said carrier body.
8. The x-ray anode according to claim 1, wherein said intermediate layer between said first and second emission layers comprises at least one material selected from the group consisting of molybdenum, tungsten, copper, an alloy based on tungsten, an alloy based on molybdenum, an alloy based on copper, a tungsten-copper composite material, a copper composite material, a particle-reinforced copper alloy, a particle-reinforced aluminum alloy and graphite.
9. The x-ray anode according to claim 1, wherein said carrier body comprises at least one material selected from the group consisting of molybdenum, tungsten, copper, an alloy based on tungsten, an alloy based on molybdenum, an alloy based on copper, a tungsten-copper composite material, a copper composite material, a particle-reinforced copper alloy, a particle-reinforced aluminum alloy and graphite.
10. The x-ray anode according to claim 1, wherein said intermediate layer is one of a plurality of intermediate layers.
11. The x-ray anode according to claim 1, wherein said intermediate layer comprises at least one barrier layer.
12. The x-ray anode according to claim 1, wherein said intermediate layer comprises at least one binding layer.
13. The x-ray anode according to claim 1, wherein the x-ray anode is configured as a stationary anode or a linear anode.
14. The x-ray anode according to claim 1, wherein the x-ray anode is configured as a rotary anode.
15. The x-ray anode according to claim 14, wherein said first emission layer and said at least one second emission layer are annular layers arranged one above another in the central direction.
Description
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
(1) There is shown in a representation that is not to scale:
(2) FIG. 1: a sectional representation of a stationary anode;
(3) FIG. 2: a perspective representation of a linear anode;
(4) FIG. 3: a sectional representation of the linear anode from FIG. 2 along the sectional plane I-I;
(5) FIG. 4: a plan view of a rotary anode;
(6) FIG. 5: a sectional representation of the rotary anode from FIG. 4 along the sectional plane II-II;
(7) FIG. 6: an axonometric view of the rotary anode from FIG. 4;
(8) FIG. 7: a flow diagram of a powder-metallurgical process for producing a rotary anode;
(9) FIG. 8a: a side view of a sintered component;
(10) FIG. 8b: a section through the sintered component from FIG. 8a;
(11) FIG. 9a: a plan view of a forging blank;
(12) FIG. 9b: a section through the forging blank from FIG. 9a.
DESCRIPTION OF THE INVENTION
(13) FIG. 1 shows a schematic sectional representation of a stationary anode 10, the basic construction of which is known in the prior art. In a known way, arranged on a substantially cylindrical carrier body 13, on its beveled front side that is facing the electron beam during operation, is a first emission layer 14, to which high-energy electrons are accelerated during operation, x-radiation being generated in interaction with the material of the emission layer. The stationary anode according to the invention differs from the prior art by a second emission layer 15, which is in the interior of the stationary anode and is arranged at a distance in the central direction 17 from the first emission layer. The central direction 17 corresponds to the axial direction of the stationary anode 10. The intermediate layer 16 separates the two emission layers 14, 15 and protects the at first inactive second emission layer 15 from the electrons impinging on the first emission layer. When the first emission layer 14 is no longer suitable for further operation, the second emission layer 15 is exposed and comes to be used for generating x-radiation. Therefore, the stationary anode according to the invention can still be used after the first emission layer has worn away, and only has to be reworked or renewed when both emission layers are unusable. The stationary anode 10 according to the invention therefore has a lifetime that is approximately twice as long as a stationary anode of the prior art. The geometry and position of the second emission layer 15 are preferably adapted to those of the first emission layer 14, so that, when the emission layer is changed, apart from a displacement in the central direction the stationary anode does not have to be laboriously readjusted. The first emission layer 14 and the second emission layer 15 are parallel to one another and are congruent in the viewing direction along the central direction 17.
(14) FIG. 2 and FIG. 3 show the application of the idea according to the invention to a linear anode 11. An example of a linear anode of the prior art is described in WO 2013/020151 A1. Linear anodes have an elongated extent along one direction of extent, in the present exemplary embodiment a bar-shaped basic form, wherein the main direction of extent of the anode does not necessarily have to run along a straight line but may also go along a curved line. This means that even a cuboid that has a curvature at least over part of its profile should be understood within the scope of the present invention as a linear anode. The first emission layer 14 and the second emission layer 15 are arranged on the side surface of the cuboidal carrier body that is facing the electron beam during operation. The first emission layer 14 is of an elongate configuration and defines a plane that is perpendicular to the central direction 17. The first emission layer 14 and the second emission layer 15 are arranged a distance apart in the central direction 17, separated by an intermediate layer 16. The distance between the two emission layers 14, 15 is constant over the surface-area extent of the emission layer. Preferably, the first emission layer 14 and the second emission layer 15 are congruent in the viewing direction along the central direction 17. By analogy with the stationary anode, the second emission layer 15 only comes to be used when the necessary yield from the x-ray dose can no longer be achieved with the first emission layer 14 and the first emission layer 14 and the intermediate layer 16 have been ground away to allow the linear anode to be used further.
(15) In FIGS. 4 to 6, a rotary anode 12 according to the invention with a plate-shaped, rotationally symmetrical carrier body 13 is schematically represented. As in the case of rotary anodes known in the prior art, on the side that is facing the electron beam during operation, a first emission layer 14 is arranged in an annular region at the beveled shoulders of the carrier body. This region corresponds to the region of impingement 50 of the electrons during the operation of the rotary anode. By analogy with the previous embodiments, the rotary anode 12 according to the invention has apart from a first emission layer 14 a second emission layer 15, which is arranged a distance apart in the central direction 17, separated by an intermediate layer 16. The central direction 17 is given by the direction of the axis of rotation of the rotary anode. In the present exemplary embodiment, the second emission layer 15 extends beyond the region of impingement 50 of the electrons into an inner region. As explained below, there are powder-metallurgical production-related reasons for this, but it is clearly not absolutely necessary. When the first emission layer 14 is no longer suitable for further use, it and the intermediate layer 16 are removed. Preferably, during the grinding or turning on a lathe of the rotary anode, that part of the second emission layer 15 that is located in the inner region, that is to say outside the region over which the first emission layer extends, is also removed. The second emission layer 15, as the active emission layer, then has the same extent as the first emission layer 14. The first emission layer 14 and the second emission layer 15 are arranged parallel to one another and, in the case of the present rotary anode, the two emission layers 14, 15 are congruent in a viewing direction along the central direction 17 in the region of impingement 50 of the electrons. The geometry of the two emission layers 14, 15 is therefore made to match one another, in order that, apart from a displacement in the central direction, no further adaptations of the rotary anode are necessary when the active emission layer is changed. Preferably, the material of the first emission layer 14 and the second emission layer 15 is also made to match one another and the same material is used for the two emission layers 14, 15, so that the emitted radiation spectrum of the x-ray anode also does not alter when the active emission layer is changed.
(16) During the operation of the rotary anode, the intermediate layer 16 protects the at first inactive second emission layer 15 from the impinging electrons and should be dimensioned with sufficient thickness in order that no instances of premature damage due to interaction with impinging electrons occur. A distance (in the central direction) between the two emission layers of between 2 and 5 mm has proven to be advantageous, since as a result on the one hand sufficient protection under the commonly occurring loads could be ensured, on the other hand the moment of inertia of the rotary anode is not significantly increased by the additional mass. In order to ensure good onward heat conduction, the first emission layer is connected to the intermediate layer in a material-bonding manner, and the second emission layer is connected to the intermediate layer and to the carrier body in a material-bonding manner. It also proves to be an advantage if the intermediate layer represents a barrier against the further spread of cracks, such as are produced in the active emission layer. The intermediate layer 16 may also form a barrier against the diffusion of harmful substances into the emission layers (for example of carbon from the commonly used carrier body material TZM or MHC). It is also advantageous if the intermediate layer 16 improves the binding attachment of the emission layer to the carrier body. The intermediate layer 16 may for this purpose be made up of a number of different layers with differing functionality, in particular of a barrier layer and/or a binding layer.
(17) FIG. 7 shows on the left the flow diagram for a powder-metallurgical process for producing an x-ray anode according to the invention, in particular a rotary anode. The production process according to the invention is primarily suitable for the production of a metallic carrier body from a refractory metal or from an alloy on the basis of a refractory metal such as TZM or MHC and comprises at least the following steps: filling a pressing mold with a powder or a powder mixture for the carrier body pressing the powder or the powder mixture to form a molding applying the powder or the powder mixture for the second emission layer to the molding obtained in the previous step pressing the component obtained in the previous step to form a molding applying the powder or the powder mixture for the material of the intermediate layer to the molding obtained in the previous step pressing the component obtained in the previous step to form a molding applying the powder or the powder mixture for the first emission layer to the molding obtained in the previous step pressing the component obtained in the previous step to form a molding sintering the molding at temperatures greater than 2000 C. forging the sintered molding at temperatures greater than 1300 C. optionally final machining to form an x-ray anode, in particular a rotary anode.
(18) Schematically indicated on the right in FIG. 7 are the intermediate products produced in individual steps of the process and the final product in the example of a rotary anode. In this case, the pressing blank is denoted by 18,18,18,18, the sintered blank by 19, the forging blank by 20 and the finished rotary anode by 12.
(19) FIG. 8a, FIG. 8b, FIG. 9a and FIG. 9b show some of these intermediate products on the basis of a specific exemplary embodiment in which a TZM powder is used as initial powder for the carrier body and a W95Re5 powder is used for the two emission layers. The powders were layered in a way corresponding to process steps previously described, pressed at pressures of up to 50 kN/cm.sup.2 and subsequently sintered at a temperature of about 2000 C. to 2400 C. The sintered component 19 thus obtained is represented in FIG. 8a in a side view and in FIG. 8b in a sectional side view. Subsequently, the sintered component was forged in an impact bonding press at temperatures above 1300 C. to form a component with hanging shoulders. The forging blank 20 is depicted in FIG. 9a in a plan view from above and in FIG. 9b in a sectional representation. In the case of these prototypes, for production-related reasons the emission layers 14, 15 extend over the entire extent of the component, but for mass production it may of course be provided that the powder for the emission layers is only applied in the ultimately required region at the hanging shoulders. The forging blank is subsequently remachined, including that the first emission layer is ground away in the inner region that is not required. To increase the heat radiating capability, a radiating body may be arranged (in a known way) on the side of the rotary anode that is opposite from the focal track side.
