Patent Grant
11145482
The disclosure relates to a target, a radiation source, a use of a radiation source and a method for producing a target. In particular, the disclosure relates to a target having an exposed surface of a target element. With the use of a corresponding radiation source with the target element, the exposed surface can be irradiated with particles, in particular electrons, in order to generate invasive electromagnetic radiation.
Invasive radiation, in particular X-ray radiation, is used for industrial computed tomography applications (CT). The image quality of the resulting radiographs of the object examined is dependent, inter alia, on the power density (radiant flux density) of a particle beam (in particular of an electron beam) which, in order to generate the invasive radiation, is radiated onto a so-called target of a radiation source, in which the invasive radiation arises. The particles are decelerated in the target, as a result of which the invasive electromagnetic radiation arises as so-called bremsstrahlung. The region in which the particles interact spatially with the target is also referred to as a focal spot. The power density of the particle beam is intended to be as high as possible for many applications in order to achieve a high radiation power of the invasive radiation and thus a good image quality. However, if the particle beam has an excessively high power density, the target can be vaporized at the focal spot and thus damaged.
One possibility for avoiding such damage consists in expanding the particle beam. The focal spot on the target is then enlarged and the radiant flux density decreases. However, the larger spot size caused by this on the target corresponds to a lesser degree to a point radiation source of the electromagnetic radiation emanating from the source, reduces the image sharpness of the radiographs and thus also reduces the achievable image quality.
A smaller spot size can be employed if the power of the invasive radiation is reduced. With low power, however, known detectors for detecting the invasive radiation and for generating the radiographs of the object generate images having a low signal-to-noise ratio.
US2016/0351370 discloses an X-ray radiation source in which a plurality of regions aligned with one another are exposed to an electron beam. For this purpose, X-ray targets are formed from layers of a radiation-generating material, wherein the individual layers are each in close thermally conductive contact with a substrate. The amount of heat that can be dissipated from the X-ray target is increased as a result, which allows more intense irradiation with the electron beam.
Further technological background is found in US2018/0358197, JP2002313266 A and U.S. Pat. No. 5,148,462 A.
It is an object to provide a solution for generating invasive electromagnetic radiation which makes it possible to emit electromagnetic radiation with a high radiation power in conjunction with a small spot size.
The inventor has generally recognized that an alternative to expanding the particle beam is required. The alternative may include, in particular, improved heat dissipation of the heat that arises during deceleration of the particles from the target. Improved heat dissipation from the target enables a higher power density of the impinging particle radiation, without damage to the target occurring.
The object can, for example, be achieved by a target, a radiation source and a method according to the disclosure.
A target for a radiation source of invasive electromagnetic radiation includes at least one target element, which is configured to generate invasive electromagnetic radiation upon irradiation with particles and which is coupled to a substrate arrangement for dissipating heat from the target element. The target element furthermore has a peripheral surface and thus a surface which extends peripherally in a self-contained manner and which forms a first part of the outer surface of the target element. The outer surface of the target element is additionally formed by a side surface of the target element, wherein an extent of the side surface defines a thickness of the target element, wherein a peripheral line, and thus a marginal line, extending peripherally in a self-contained manner, of the side surface forms a marginal line of the peripheral surface. The target furthermore has an end face, as part of which the side surface of the target element is arranged in an exposed manner for irradiation with the particles. The substrate arrangement is in contact with the peripheral surface.
As mentioned, the invasive electromagnetic radiation can be X-ray radiation, in particular for industrial CT applications in which workpieces are transilluminated in order to create radiographs. The target element can generally be configured to emit bremsstrahlung in the form of X-ray radiation or invasive radiation having a different wavelength upon irradiation with a particle beam (for example in the form of an electron beam or a proton beam).
For this purpose, the target element can be made of a suitable material, such as, for example, tungsten (see below).
The target is embodied in particular as a non-transmissive target, that is, as a reflection target. Such targets are also referred to as direct emitters. The power of the particle beam (and in particular of a possible electron beam) can be 500 W, for example. A resolution of the electromagnetic radiation generated, and in particular of possible X-ray radiation, can be between 1 μm and 5 μm. The focal spot size can be between 10 μm and 200 μm and for example between 5 μm and 10 μm.
The substrate arrangement preferably includes a material having a high coefficient of thermal conductivity in comparison with metals and a high melting point. Additionally or alternatively, the material can be electrically insulating. In particular, the material can be configured to emit no electromagnetic radiation, and primarily no X-ray radiation, when the particle beam impinges on the material. Heat transfer from the target element to the material of the substrate arrangement is ensured via the substrate material being contacted with and/or connected to the peripheral surface of the target element. By way of example, it is possible to provide a direct contact between the target element and the substrate arrangement and/or an indirect contact via intermediate material for securing the target element to the substrate arrangement, such as a solder layer, for example. The substrate arrangement can furthermore include at least one substrate element that is preferably substantially block-shaped and/or extends along the target element (in particular along the entire length thereof).
The peripheral surface of the target element can be (for example in the case of a cylindrical and/or wire-shaped embodiment explained below) an outer peripheral surface extending in a curved manner at least regionally. In the case of a target element embodied in a layerlike manner and explained below, the peripheral surface can have a respective surface at the top side and underside of the target element, and also two lateral surfaces, that is, side surfaces, connecting these surfaces. To put it another way, the peripheral surface in this case can have two of the side surfaces of the substantially prismatic or parallelepipedal target layer, which are connected by corresponding bottom and/or top surfaces of the target layer. In this case the peripheral surface does not include a front and a rear side surface of the target layer, one of which is arranged in an exposed manner for irradiation with particles.
The thickness of the target element can be a layer thickness of this element or a diameter in the case of a wire-shaped embodiment. Generally, the thickness can refer to a dimension of the target element that is to be measured in a direction extending substantially perpendicularly to an impinging particle beam. The thickness can delimit the focal spot. This is the case if the particle beam has a larger dimension than the target element in the direction of the thickness.
The end face of the target can likewise extend substantially perpendicularly to an impinging particle beam or else in an inclined manner with respect thereto. Furthermore, the end face can be embodied as curved, and in particular convexly curved, wherein the curvature can generally extend in the direction of the impinging particle beam (that is, toward the particle beam). The exposed side surface of the target element can be aligned with the other portions of the end face and/or the entire end face of the target can be substantially planar. An exposed side surface means that the latter is exposed for irradiation with the particles and/or is not shielded by further materials or elements.
The above-defined structure of the target enables particle irradiation of preferably exclusively a single side surface. By way of the longitudinal extent of the target element in the depth direction and by way of the peripheral surface of the target element, the heat that arises during irradiation can be dissipated into the depth and be guided into the substrate arrangement. Preferably, a large portion of the peripheral surface, for example more than 90% and preferably more than 95%, is in contact with the substrate material of the substrate arrangement. In any case in which, as preferred, the peripheral surface is larger than the exposed side surface, the energy input effected by way of the exposed side surface can be transported away by virtue of a comparatively large contact area directly from the target element into the substrate arrangement, without the energy input resulting in damage to the target. The power density of the impinging particle beam can thus be increased, without the particle beam having to be expanded. Furthermore, the structure according to the disclosure makes it possible that even in the case of incipient wear at the exposed side surface of the target element (for example in the case of erosion) there is still enough material volume available to avoid changes in the intensity of the electromagnetic radiation generated. An arbitrary amount of material can be situated in the depth direction, that is, in a direction transversely with respect to the surface of the side surface, since a substrate as carrier of the target material is not required in the depth direction. The lifetime and the available operational period of the target can thus be increased.
In the case of a wire-shaped target element, for example, the target element can be dimensioned with a length in the depth direction such that the peripheral surface is larger than the exposed side surface. The latter can be shaped like a cross-sectional area of the wire-shaped target element. In the case where the target element is embodied in a layerlike manner, the exposed side surface can likewise be shaped like a cross-sectional area and/or have a comparatively narrow (in the thickness direction) elongate (in the width direction) extent. On account of a large ratio between width and thickness of the exposed side surfaces, only a small dimension in the depth direction is required, such that the peripheral surface of such a target layer is larger than the exposed side surface.
In accordance with a further embodiment, the target element has a polygonal basic contour having different side lengths. In this case, the side surface defines in particular a side of the basic contour which does not have the largest side length. The basic area thus has sides having a larger length, in particular in the depth direction. In particular, a rectangular basic area can be involved.
In one configuration, the basic contour is rectangular and has two longer sides and two shorter sides. In this case, the exposed side surface preferably forms or contains the shorter side.
As mentioned, according to the disclosure, the target element is embodied in a layerlike manner. In this case, the exposed side surface of the target element defines a thickness and a larger width of the target element in comparison with the thickness, that is, the target element has a larger width in comparison with the thickness, wherein a total length of the peripheral line is defined by the thickness and by the width. In the exemplary case of a rectangular side surface, the total length of the peripheral line is equal to double the thickness plus double the width. However, the configuration with a layerlike target element is not restricted to a rectangular side surface. The substrate arrangement is in contact with the peripheral surface, preferably over the whole area, at sides thereof which are opposite one another in the direction of the thickness. Therefore, heat that arises in the target element is transported away rapidly via the correspondingly large total contact area to the substrate arrangement. However, in the case of other forms of the target element, too, such as, for example, the wire-shaped form that will also be described below, it is preferred for the substrate arrangement to be in contact with the peripheral surface at sides thereof that are opposite one another, in particular over the entire length of the target element in the depth direction. In the case of the layerlike target element, it is preferred for the substrate arrangement to be in contact with the peripheral surface over the whole area, specifically preferably partly indirectly by way of solder material and partly directly by way of press contact. Optionally, the whole-area contact excludes only the side surfaces of the peripheral surface, that is, those side surfaces which define the extent of the target element in the depth direction and the thickness direction.
The thickness of the target element, and in particular a possible layer thickness thereof, can generally be chosen to be smaller than a thickness of the substrate arrangement, wherein the thickness of the substrate arrangement and the thickness of the layer are to be measured parallel to one another. In this case, any of the thickness dimensions mentioned above can extend parallel to or in the end face of the target and/or substantially perpendicularly to a path direction or beam axis of the impinging particle beam.
The layerlike target element can have a constant layer thickness in the depth direction.
According to the disclosure, at the exposed side surface, the thickness of the layerlike target element increases in the width direction. In particular, the thickness can increase continuously and for example linearly in the width direction, such that the side surface is embodied in a trapezoidal fashion. More generally, at the exposed side surface, the layerlike target element can have a thickness that varies as viewed along its width, for example a layer thickness that increases or decreases continuously over the entire extent in the width direction or a part thereof. Depending on the partial region of the exposed side surfaces onto which the impinging particle beam is directed, the focal spot size can thus vary if the cross section of the particle beam impinges on a partial region of the end face of the target in which an edge of the exposed side surface is situated. The material of the target beyond the edge of the target element does not contribute to the generation of invasive radiation.
In accordance with a further embodiment, the target element is embodied in a cylindrical fashion, wherein the side surface forms an end surface of the target element that is elliptic or circular in a front view of the target element. In this context, the target element can have a basic area which is circular or oval, for example, and a material volume extending along a longitudinal axis of the target element. The latter can in turn define a peripheral surface of the target element. In one variant, the target element is embodied in a wire-shaped manner, wherein it can once again generally be shaped in an elongate manner and preferably has a circular cross section. The exposed side surface can be shaped in accordance with a cross-sectional shape of the cylindrical target element and/or define the shape. In one variant, the exposed side surface is circular and defines a diameter and thus a thickness of the wire-shaped target element. The dimensions of the diameter can be for example, between 3 μm and 200 μm and be for example up to 10 μm or up to 20 μm.
The wire-shaped target element can be received at least in portions in a receiving structure of the substrate arrangement. The receiving structure can include a groove having, for example, a V-shaped or rectangular cross-sectional shape. In the case of a multipartite embodiment of the substrate arrangement as explained below, a corresponding receiving structure (for example a groove) can be provided in a first substrate element, wherein a second substrate element closes the groove at least in portions (for example closes in portions the cross section of the groove that is open at least on one side). Alternatively, the receiving structure can include a hole, which can extend in particular substantially transversely with respect to the end face and/or into which the target element is inserted.
An embodiment provides for the target to include a plurality of target elements having different thicknesses. The target elements can be produced from an identical material and/or have substantially identical lengths, for example as viewed orthogonally to the end face of the target. The target elements can in turn each include exposed side surfaces in an end face of the target and each be configured to emit invasive electromagnetic radiation upon irradiation with particles, the invasive electromagnetic radiation being usable for creating object radiographs. In order to vary the focal spot size, the electron beam can alternate between the target elements or, to put it another way, irradiate target elements with different thicknesses. The exposed side surfaces can be arranged along a common and preferably rectilinear line. This makes it possible for the electron beam to be directed onto the different target elements in a simple manner, for example via a linear relative movement of target and electron beam or a relative rotation during which the electron beam is moved linearly over the target.
In this context, provision can furthermore be made for the target to have a plurality of wire-shaped target elements having different thicknesses or diameters, which are preferably in turn arranged in a common row within the end face of the target and are exposed. The focal spot size can be varied in this case by virtue of the fact that irradiation with the particle beam alternates between the wire-shaped target elements (that is, successively different target elements are irradiated).
An embodiment provides for the substrate arrangement to enclose the target element at least in portions. This can be effected by a wire-shaped target element being received in a receiving structure (for example in a groove) in the manner outlined above and the receiving structure being covered with a further element of the substrate arrangement. To put it more generally, the target element can be received between individual substrate elements of the substrate arrangement in a sandwichlike manner.
In a variant, the substrate arrangement includes a first and a second substrate element, which receive between them at least one portion of the target element. In this case, the substrate elements can preferably be pressed against one another, for example via mechanical securing or clamping elements or by a heat dissipating element or heat dissipating arrangement, explained below. The substrate elements can each be embodied in a block-shaped fashion and/or be embodied in such a way that the target element bears against them as much as possible over the whole area (for example bears against them via at least one substantially complete bottom or top surface). In a variant, the substrate elements extend along the entire length of the target element in the depth direction.
An embodiment provides for the substrate arrangement to be received in a heat dissipating element or in a heat dissipating arrangement, which is preferably connected or connectable to a cooling device. The cooling device can be provided externally in relation to the target and can be for example a part of a radiation source explained below. The heat dissipating element or the heat dissipating arrangement can be embodied in a block-shaped or tubular fashion and/or include a receiving portion for the substrate arrangement. Additionally or alternatively, the heat dissipating element or the heat dissipating arrangement can define a cavity into which the substrate arrangement is inserted and/or pushed. In the case of a plurality of substrate elements, the heat dissipating element or the heat dissipating arrangement can be configured, for example, by exerting a press-on or compressive force, to hold the substrate elements together and/or to press them against one another. Generally, it is possible to provide for bearing between the heat dissipating element (or the heat dissipating arrangement) and the substrate arrangement at least in portions in order to enable a good heat transfer to the heat dissipating element or the heat dissipating arrangement. For connection to the cooling device, the heat dissipating element or the heat dissipating arrangement can include a suitable connection region. Additionally or alternatively, the heat dissipating element or the heat dissipating arrangement can include at least one cooling duct into which a coolant is able to be introduced.
The substrate arrangement, too, can be connected or connectable to a cooling device. By way of example, the substrate arrangement can likewise include a cooling duct and/or a receiving region in which a cooled line of the cooling device is able to be received. In a variant, a coolant of the cooling device flows and/or washes around the substrate arrangement at least in portions.
In accordance with an embodiment, the target has a substrate arrangement including diamond or a diamond-containing material, and/or the target has a target element which is made of tungsten, and/or the heat dissipating element or the heat dissipating arrangement includes copper.
In the region of the end face, regions of the target element that lie away from the exposed side surface, and in particular the side surface of the substrate arrangement, can be covered with a material layer. The material of this layer can be chosen in such a way that charging of electrons in the substrate arrangement is substantially suppressed or at least limited. The generation of an opposing electric field with respect to the electron beam can be avoided as a result. In particular, this layer can consist of a metallic material, a semiconductor material or carbon.
As an alternative to the above approaches of irradiating a side surface in the target, a target is furthermore disclosed in which tungsten particles are introduced into a light metal matrix. In the context of cooling of such a composition, the tungsten particles can deposit at an underside of the target. The particle density should be chosen in such a way that the particles occupy a proportion of approximately 10% of the area of the underside. The underside can then be irradiated with an electron beam in order to generate X-ray radiation. However, the melting point of the light metal matrix can limit the beam power of the electron beam that is usable in this case.
The disclosure furthermore relates to a radiation source for generating invasive electromagnetic radiation, including a target; a particle beam source configured to direct a particle beam onto the target; and a positioning device configured to orient the target and the electron beam relative to one another in a variable manner, such that that surface region of the target onto which the particle beam is directed is variable. The particle beam can once again include electrons. The particle beam source can include a glow wire for emitting the electrons. Via the positioning device, the particle beam and the target can be rotated for example, relative to one another, for example about an axis extending perpendicularly to the particle beam. In a variant, the target is rotatable relative to the particle beam, wherein the axis of rotation can once again extend orthogonally to the particle beam.
Via the positioning device, the particle beam can be directed onto different surface regions of the exposed side surface of the target element. In the case of a constant thickness of the target element, this can be used to compensate for local wear (that is, the particle beam can, if necessary, be directed onto a portion that is not yet worn). In the case of a varying thickness (for example in the case of a trapezoidal side surface of the target element), the focal spot size can also be varied via the positioning device.
Moreover, the disclosure relates to a method of using a radiation source of the type described above, including the following steps:
In the case of just one target element, the regions having different thicknesses can be defined by a trapezoidal shape of an exposed side surface of the target element. In the case of a plurality of target elements, the latter can each have mutually different thicknesses and thus each define by themselves one of the regions having different thicknesses within the end face of the target. This can be achieved for example, by the target including a plurality of wire-shaped target elements having mutually different diameters.
The method can generally include any further step and any further feature in order to provide all of the operating states, effects and/or interactions discussed above and below. In particular, the method can include a step of cooling the substrate arrangement or a possible heat dissipating element or heat dissipating arrangement.
In addition, the disclosure relates to a method for producing a target for a radiation source of invasive electromagnetic radiation, in particular a target in one of the configurations described in this description. In accordance with the method,
Features of configurations of the method are evident from the description of configurations of the target.
The invention will now be described with reference to the drawings wherein:
The radiation source 1 includes an electron beam source 12 indicated schematically. The electron beam source 12 forms a particle beam source for emitting electrons. The electron beam source 12 is configured to emit particles in the form of electrons along a particle beam axis A and to direct them onto the target 10. Various coils for orienting and focusing the electron beam are positioned along the particle beam axis A. To put it more precisely, as viewed proceeding from the electron beam source 12 and in the direction of the target 10, firstly a first and a second beam deflecting unit 14, 16 are provided, via which the orientation of the beam axis A is inherently variable. Furthermore, a focus coil 18 is provided, which includes an aperture 19 and via which a focal plane of the electron beam is able to be set. In a known manner, the focal plane can be positioned in the region of the target 10 or slightly in front of or behind it. Furthermore, the illustration does not show that a copper tube surrounding the beam axis A can be provided at least in the region of the beam deflecting units 14, 16 and the focus coil 18.
The target 10 is likewise shown in plan view in
The target 10 has a slightly convexly curved end face 22 facing the electron beam. As explained below, the end face 22 is also inclined relative to the electron beam and also relative to the plane of the drawing. If the electron beam impinges on the end face 22 and penetrates into the material of the target 10, it is decelerated, whereupon X-ray radiation is emitted. An X-ray used beam cone emerges along an axis SA through a stop 24 into the surroundings and, after radiating through an object, is incident on a detector device, not illustrated, in order to generate a radiograph of the object.
The target 10 is furthermore coupled to a positioning device 26 (or else adjustment mechanism). The positioning device 26 makes it possible to rotate the target 10 about an axis V that is perpendicular to the plane of the drawing. The end face 22 of the target 10 can thus also be rotated relative to the electron beam. As can be inferred from the view in
As can furthermore be derived from the illustration in
The target element 20 is received in a substrate arrangement 28 consisting of diamond produced for example, via a CVD (chemical vapor deposition) method. The substrate arrangement 28 includes a first substrate element 30 and a second substrate element 32. The surfaces of the target element 20 that are at the top and bottom in the illustration in
The substrate arrangement 28 itself is received in a heat dissipating arrangement 34, for example, composed of copper, which is in turn embodied in a bipartite fashion. To put it more precisely, the heat dissipating arrangement 34 encloses the substrate arrangement 28 and bears against the substrate arrangement 28 over a large area at the largest outer surfaces of the substrate arrangement. Furthermore, at least one cooling duct 36 is provided in the heat dissipating arrangement 34, a coolant for transporting heat away flowing through the at least one cooling duct. The cooling duct 36 is connected to a cooling device (not illustrated) of the radiation source 1.
In
The above-explained basic construction of the target 10 is explained in greater detail below. Firstly,
The target element 20 is embodied in a layerlike manner. In the embodiment shown, the layer thickness D is constant in this case. Furthermore, the layer thickness D is chosen to be comparatively thin and is for example, at least 10 μm, preferably at least 20 μm, and/or for example, at most 200 μm, preferably at most 100 μm. It is evident that a respective thickness C of the substrate elements 30, 32 exceeds the layer thickness D of the target element 20 by a multiple, for example, at least by five-fold and preferably at least by ten-fold. All of the thickness dimensions C, D explained above here extend perpendicularly to the depth direction in which the target element extends with a depth T. If the target 10 is used in an arrangement as shown in
Furthermore,
The width B is preferably at least 1 mm or at least 2 mm, particularly preferably at least 4 mm, and in practice can be for example, 5 mm. Therefore, the width B can be greater than the layer thickness D in particular at least by a factor of 20, 50 or 100. Consequently, it is possible to limit the size of a focal spot in the direction of the layer thickness D, while in the direction of the width B a large region is available for the focal spot, for example, for generating X-ray radiation. The size of the focal spot in the direction of the width B can at any time be significantly smaller than the width B. For example, the size of the focal spot in the direction of the width B can be greater than 10 μm or 20 μm and/or less than 200 μm or 100 μm and be for example, 60 μm. The width B can be greater than the size of the focal spot in the direction of the width B for example, at least by a factor of 5, 10 or 50.
The target element 20 is thus received in the substrate arrangement 28 along its entire length L, wherein the substrate arrangement 28 is likewise received in the heat dissipating arrangement 34 along its entire length. “Received” means, in particular, that the surfaces of the mutually adjoining layers of the target element and of the substrate arrangement are in contact with one another over the whole area. The resulting large-area bearing regions enable comprehensive heat exchange between these elements and, in particular, dissipation of heat from the target element 20 into the substrate arrangement 28 and from the latter into the heat dissipating arrangement 34.
In the embodiment, the target element 20 furthermore has a substantially rectangular basic contour or, to put it another way, a substantially rectangular basic area. The latter includes two shorter sides 2 and two longer sides 3, which respectively run parallel, as shown by the enlarged illustration only of the target element 20 in
On account of the layerlike configuration of the target element 20, the latter can be embodied in a parallelepipedal fashion (as illustrated in
This has the consequence that a comparatively small proportion of the material of the target element 20 is exposed for irradiation with the electrons and that, by contrast, a correspondingly large proportion of material adjoins and remains at the substrate material of the substrate arrangement 28 in order to dissipate heat directly into the substrate arrangement 28 and to compensate for possible erosion of the target element 20.
This relationship is furthermore elucidated by closer consideration of the substrate arrangement 28. As mentioned, the substrate elements 30, 32 of the substrate arrangement 28 are embodied substantially in a block-shaped manner and are embodied with a larger thickness C in comparison with the target element 20. It is evident that a first, lower substrate element 30 in
In order to couple the substrate arrangement 28 and the target element 20, the target element 20 can be soldered to one of the substrate elements 30, 32, in particular using an already known solder material including copper, silver, gold or tin and nickel, for example. The remaining substrate element 30, 32 can then be pressed onto the respectively remaining top side or underside of the target element 20. A corresponding press-on force can be effected by way of mechanical securing or clamping means (not illustrated). The latter can also be provided for fixedly clamping the two parts of the bipartite heat dissipating arrangement 34 against one another, wherein a corresponding press-on force is able to be transmitted from the heat dissipating arrangement 34 to the substrate elements 30, 32 as well.
Finally, it should be pointed out that in the end face 22 the exposed (or optionally coated) surfaces of the substrate elements 30, 32 of the heat dissipating arrangement 34 and also the exposed side surface 38 of the target element 20 can be aligned with one another, but this is not absolutely necessary. The end face 22 of the target 10 can thus have a substantially smooth surface, wherein provision can also be made of a curvature—not illustrated separately in
As explained, the target element 20 is embodied with a constant thickness D corresponding to a height of the side surface 38 in the illustration in
In contrast to the previous embodiment, however, a layer thickness D of the target element 20 is not constant along the width B of the target element 20. Instead, it varies, with the result that a cross-sectional shape of the target element 20, and thus a shape of the exposed side surface 38, is trapezoidal, as is discernible in
The generation of X-ray radiation is explained in greater detail below with reference to
Referring firstly to
In the case of this embodiment in accordance with the prior art, the end face 22 is formed by an anode material (that is, target material suitable for generating invasive radiation) over the whole area. This can be achieved, for example, by virtue of the fact that a corresponding target element 20 is embodied as a layer, but this layer completely covers an underlying substrate end face of the target 10 and is applied thereto areally.
The electron beam E impinges on the inclined end face 22 in an elliptic region of impingement or interaction, thus giving rise to the elliptically shaped focal spot 40 illustrated on the right in
The illustration in
In summary, it becomes clear from
The target elements 20 are embodied in a wire-shaped manner and with a circular cross section and, analogously to the layerlike configuration in accordance with the embodiment shown in
Only one target element 20 is provided in the variant in
Consequently, when an electron beam impinges on the exposed side surface 38, a focal spot size is crucially determined by way of the thickness D of the wire-shaped target element 20. The thickness D can in turn be chosen in such a way that small spot sizes or cross-sectional areas of the emitted X-ray radiation S2 are achievable. By way of example, if the impinging electron beam E has a diameter that exceeds the thickness D, the thickness (or the diameter of the wire-shaped target element 20) correspondingly limits the resulting focal spot 40, as a result of which the spot size of the emitted X-ray radiation S2 is also limited (cf.
Although only a single target element 20 is shown in
By contrast,
Since the focal spot size is crucially determined by the thickness of the target element 20 in the embodiments shown, the requirements in respect of focusing of the electron beam can also be reduced. By way of example, electron beam focusing that is possibly not highly accurate is likely to affect, rather, an efficiency of the radiation source 1 in the sense of a ratio of the power of the electron beam source 12 to the X-ray radiation obtained. By contrast, the focal spot size remains comparatively stable even in the case of imprecise focusing, such that a substantially constant resolution is achievable. This can be achieved by virtue of the fact that a region of impingement of the electron beam E on the target element 20, which region is possibly too large or too small on account of imprecise focusing, has no effect since the resulting focal spot 40 is predefined and restricted anyway by the thickness D of the target element 20.
It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102018201245.8 | Jan 2018 | DE | national |
This application is a continuation application of international patent application PCT/EP2019/051884, filed Jan. 25, 2019, designating the United States and claiming priority from German application 10 2018 201 245.8, filed Jan. 26, 2018, and the entire content of both applications is incorporated herein by reference.
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| Number | Date | Country | |
|---|---|---|---|
| 20200396818 A1 | Dec 2020 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2019/051884 | Jan 2019 | US |
| Child | 16940174 | US |
