DE102018010288B4 - Radiation source target, radiation source for generating invasive electromagnetic radiation and method of making a radiation source target - Google Patents

Abstract

Target (10) for a radiation source (1) of invasive electromagnetic radiation, having a plurality of target elements (20), which are each set up to generate invasive electromagnetic radiation when irradiated with particles, and each having a substrate arrangement (28) coupled for dissipating heat from a respective target element (20), each target element (20) having a peripheral surface forming a first portion of an outer surface of each target element (20), the outer surface of each target element (20) being further defined by a side surface ( 38) of the respective target element (20), an extension of the side surface (38) defining a thickness (D; D1, D2, D3) of the respective target element (20), a peripheral line of the side surface (38) being an edge line of the peripheral surface forms, wherein the target (10) has an end face (22), as part of which the side faces (38) of the target elements (20) for irradiation m are arranged exposed with the particles, and wherein the substrate arrangement (28) is in contact with the peripheral surfaces of the target elements (20), the target elements (20) having different thicknesses (D1, D2, D3) and the exposed side surfaces (38) of the target elements (20) are arranged along a common line, characterized in that the substrate assembly (28) comprises a first substrate element (30) and a second substrate element (32) sandwiching at least a portion of the respective target elements (20).

Description

The invention relates to a target, a radiation source and a method for producing a target. In particular, the invention relates to a target having exposed surfaces of a plurality of target elements. When using an appropriate radiation source with the target elements, the exposed surface can be irradiated with particles, in particular electrons, in order to generate invasive electromagnetic radiation.

Invasive radiation, particularly X-rays, is used for industrial computed tomography (CT) applications. The image quality of the resulting radiographic images of the examined object depends, among other things, on the power density (radiation flux density) of a particle beam (in particular an electron beam) which, in order to generate the invasive radiation, is irradiated onto a so-called target of a radiation source in which the invasive radiation is produced. The particles are decelerated in the target, which results in the invasive, electromagnetic radiation as so-called reflex radiation. The spatial interaction area of the particles with the target is also called the focal spot. The power density of the particle beam should be as high as possible for many applications in order to achieve high radiation power of the invasive radiation and thus good image quality. However, if the particle beam has too high a power density, the target in the focal spot can be vaporized and thus damaged.

One way of avoiding such damage is to widen the particle beam. The focal spot on the target is then enlarged and the radiant flux density is reduced. However, the resulting larger spot size on the target corresponds less to a punctiform radiation source of the electromagnetic radiation emanating from the source, reduces the sharpness of the transmission images and thus also reduces the image quality that can be achieved.

It is possible to work with a smaller spot size if the power of the invasive radiation is reduced. However, known detectors for detecting the invasive radiation and for generating the transmission images of the object generate images with a low signal-to-noise ratio at low power.

the US 5,148,462A discloses an X-ray anode source in which a metallic target material is applied to and may also be partially surrounded by a diamond structure, but with geometrical relationships differing from the invention.

the U.S. 2015/0 117 616 A1 discloses an X-ray apparatus having a target unit in which a target material is buried in a diamond substrate.

the U.S. 8,416,920 B2 discloses a target for X-ray generation in which a target material is introduced into recesses of a substrate.

the WO 2017/ 204 850 A1 relates to a compact source for generating high brightness X-rays. The higher brightness is achieved by irradiating several mutually aligned areas with electrons. This can be achieved through the use of x-ray targets comprising microstructures of x-ray generating materials in intimate thermal contact with a high thermal conductivity substrate.

There is thus a need to provide a solution for generating invasive electromagnetic radiation that enables electromagnetic radiation to be radiated with a high radiant power with a small spot size.

The inventor has generally recognized that an alternative to expanding the particle beam is needed. This can consist in particular in improved heat dissipation of the heat generated when the particles are decelerated from the target. Improved heat dissipation from the target enables a higher power density of the incident particle radiation without damaging the target.

To this end, the invention proposes a target, a radiation source and a method according to the appended independent claims 1, 10 and 11. These appended independent claims define the scope of protection. Advantageous developments are specified in the dependent claims.

A target for a radiation source of invasive electromagnetic radiation comprises at least a plurality of target elements which are set up to generate invasive electromagnetic radiation when irradiated with particles and which are each coupled to a substrate arrangement for dissipating heat from a respective target element. The respective target elements also have a peripheral surface and thus a self-contained peripheral surface which forms a first part of an outer surface forms each target element. The outer surface of each target element is also formed by a side surface of the respective target element, with an extension of the side surface defining a thickness of the respective target element, with a peripheral line and thus a closed peripheral edge line of the side surface forming an edge line of the peripheral surface. The target further has an end surface, as part of which the side surfaces of the target elements are exposed for irradiation with the particles. The substrate arrangement is in contact with the peripheral surfaces.

As mentioned, the invasive electromagnetic radiation can be X-ray radiation, in particular for industrial CT applications in which workpieces are x-rayed to create radiographs. In general, the plurality of target elements can be set up to emit bremsstrahlung in the form of X-rays or invasive radiation of a different wavelength when irradiated with a particle beam (for example in the form of an electron beam or a proton beam). For this purpose, the target elements can consist of a suitable material or contain the material, such as tungsten (see below).

The target is designed in particular as a non-transmissive target, i.e. as a reflection target. Such targets are also referred to as direct emitters. The power of the particle beam (and in particular any electron beam) can be 500 W, for example. A resolution of the generated electromagnetic radiation and in particular of any 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 comprises a material with a high coefficient of thermal conductivity and a high melting point compared to metals. Additionally or alternatively, the material can be electrically insulating. In particular, the material can be designed not to emit any electromagnetic radiation and, in particular, no X-rays when the particle beam strikes the material. Contacting and/or connecting the substrate material to the peripheral surfaces of the target elements ensures heat transfer from the target elements to the material of the substrate arrangement. For example, a direct contact between the target elements and the substrate arrangement can be provided and/or an indirect contact via intermediate material for attaching the target elements to the substrate arrangement, such as a layer of solder. The substrate arrangement can also comprise at least one substrate element, which is preferably essentially block-shaped and/or extends along the target element (in particular along its entire length).

The peripheral surface of the target elements can (for example in the case of a cylindrical and/or wire-shaped configuration explained below) be an outer peripheral surface which is curved at least in some areas. In the case of a layered target element as explained below, the peripheral surface may have one surface each on the top and bottom of the target element, and two side surfaces connecting these surfaces, i.e. side surfaces. In other words, in this case the peripheral surface can have two of the side surfaces of the essentially prismatic or cuboid target layer, which are connected by corresponding base and/or cover surfaces of the target layer. In this case, a front and a rear side surface of the target layer, one of which is arranged exposed for irradiation with particles, do not belong to the peripheral surface.

The thickness of the target element can be a layer thickness of this element or a diameter in the case of a wire-shaped configuration. In general, the thickness can relate to a dimension of the target element, which is to be measured in a direction essentially perpendicular to an impinging particle beam. The thickness can limit the focal spot. This is the case when the particle beam has a larger dimension in the thickness direction than the target element.

The end face of the target can also extend essentially perpendicularly to an impinging particle beam or also at an angle thereto. Furthermore, the end face can be arched and in particular convexly arched, with the arching being able to extend generally towards the impinging particle beam (i.e. towards the particle beam). The exposed side surfaces of the respective target elements can be flush with the remaining sections of the end surface and/or the entire end surface of the target can be essentially flat. An exposed side surface means that it is exposed to the particles and/or not shielded by other materials or elements.

The structure of the target defined above enables particle irradiation preferably exclusively on a single side surface of a respective target element. Over the longitudinal extent of the respective target element in the depth direction and over the peripheral surface of the respective tar getelements, the heat generated during the irradiation can be dissipated in depth and introduced into the substrate arrangement. Preferably, a majority of the peripheral surface, for example more than 90% and preferably more than 95%, is in contact with the substrate material of the substrate assembly. In each case, in which the peripheral surface is larger than the exposed side surface of a respective target element, as is preferred, the energy input via the exposed side surface can be transported away directly from the target element into the substrate arrangement through a comparatively large contact surface, without the energy input damaging the target leads. Consequently, the power density of the impinging particle beam can be increased without the particle beam having to be expanded. Furthermore, the structure according to the invention enables sufficient material volume to be available even when wear begins on the exposed side surface of the respective target element (eg in the event of burning) in order to avoid changes in the intensity of the electromagnetic radiation generated. Any amount of material can be located in the depth direction, ie in a direction transverse to the surface of the side surface, since a substrate is not required as a carrier of the target material in the depth direction. The service life and the available operating time of the target can thus be increased.

For example, in the case of a wire-shaped target element, the target element can be dimensioned so long in the depth direction 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 of a layered formation of the target element, the exposed side surface can likewise be shaped like a cross-sectional surface and/or have a comparatively narrow (in the direction of thickness) elongated (in the direction of width) extension. Due to a large ratio between the width and thickness of the exposed side surfaces, only a small dimension in the depth direction is required, so that the peripheral surface of such a target layer is larger than the exposed side surface.

According to a further embodiment, the respective target element has a polygonal outline with different side lengths. In this case, the side surface defines in particular a side of this floor plan that does not have the longest side length. The base area thus has sides of greater length, particularly in the depth direction. In particular, it can be a base that is rectangular.

In one embodiment, the floor plan 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 one variant, the respective target element is formed in layers. In particular, the exposed side surface of the respective target element defines a thickness and a width of the target element that is greater than the thickness, i.e. the respective target element has a greater width than the thickness, with a total length of the peripheral line being defined by the thickness and by the width . In the case of a rectangular face, the total length of the perimeter is equal to twice the thickness plus twice the width. However, the design with a layer-like target element is not limited to a rectangular side surface. The substrate arrangement is preferably in full-area contact with the circumferential surface on opposite sides of the circumferential surface in the direction of thickness. The heat generated in the respective target element is therefore quickly transported away to the substrate arrangement via the correspondingly large total contact area. However, with other shapes of the respective target element, such as the wire-like shape described below, it is preferred that the substrate arrangement is in contact with the peripheral surface on opposite sides of the latter, in particular over the entire length of the target element in the depth direction. In the case of the respective layered target element, it is preferred that the substrate arrangement is in full-surface contact with the peripheral surface, specifically preferably partially indirectly via solder material and partially directly via pressure contact. Optionally, only the side surfaces of the peripheral surface are excluded from the full-surface contact, i. H. those side surfaces which define the extent of the respective target element in the depth direction and thickness direction.

The thickness of the respective target element and in particular any layer thickness thereof can generally be selected to be less than a thickness of the substrate arrangement, the thickness of the substrate arrangement and the thickness of the layer being measured parallel to one another. Any of the thickness dimensions mentioned above can run parallel to or in the end face of the target and/or essentially perpendicular to a direction or beam axis of the impinging particle beam.

The respective layered target element can have a constant thickness in the width direction on the respective exposed side surface. The layer thickness can also be constant in the respective depth direction.

Alternatively, the thickness of the respective layer-like target element can increase in the direction of the width at the respective exposed side surface. In particular, the thickness can increase continuously and, for example, linearly in the direction of the width, so that the side surface has a trapezoidal shape. More generally, the respective layer-like target element can have a thickness that varies along its width on the respective uncovered side surface, for example a layer thickness that continuously increases or decreases over the entire extent in the width direction or part of it. The size of the focal spot can vary depending on which part of the exposed side surface the impacting particle beam is aimed at if the cross-section of the particle beam hits a part of the end face of the target in which an edge of the exposed side surface is located. The material of the target beyond the edge of each target element does not contribute to the generation of invasive radiation.

According to a further embodiment, the respective target element is cylindrical. The respective side surface can form an elliptical or circular end surface of the target elements in a front view of the respective target element. In this context, the respective target element can have a base area which is, for example, circular or oval, and a material volume extending along a longitudinal axis of the respective target element. The latter can in turn define a peripheral surface of the respective target element. In one variant, the respective target element is designed in the form of a wire, which in turn can be generally elongate in shape and preferably has a circular cross section. The respective exposed side surface may be shaped according to and/or define a cross-sectional shape of the respective cylindrical target element. In one variant, the respective exposed side surface is circular and defines a diameter and thus a thickness of the respective wire-shaped target element. The dimensions of the diameter can, for. B. between 3 microns and 200 microns and be, for example, up to 10 microns or up to 20 microns.

The respective wire-shaped target element can be accommodated at least in sections in a receiving structure of the substrate arrangement. The receiving structure may include a groove having a V-shaped or rectangular cross-sectional shape, for example. In the case of a multi-part configuration of the substrate arrangement explained below, a corresponding receiving structure (e.g. a groove) can be provided in a first substrate element, with a second substrate element closing the groove at least in sections (e.g. closing the cross section of the groove, which is open at least on one side, in sections). Alternatively, the receiving structure can include a bore, which in particular can run essentially transversely to the end face and/or into which the target element is inserted.

The invention provides that the target comprises a plurality of target elements with different thicknesses. The target elements can be made of an identical material and/or have substantially identical lengths, for example viewed orthogonally to the face of the target. The target elements can in turn each comprise uncovered side surfaces in an end face of the target and each be designed to emit invasive electromagnetic radiation when irradiated with particles, which can be used to create object transmission images. In order to vary the focal spot size, the electron beam can switch between the target elements or, in other words, irradiate target elements with different thicknesses. The exposed side surfaces can be arranged along a common and preferably rectilinear line. This allows the electron beam to be easily aimed at the various target elements, for example by means of a linear relative movement of the target and electron beam or a relative rotation in which the electron beam is moved linearly over the target.

In this context, it can also be provided that the target has a plurality of wire-shaped target elements with different thicknesses or diameters, which are preferably in turn arranged and exposed in a common row within the end face of the target. In this case, the focal spot size can be varied by alternating irradiation with the particle beam between the wire-shaped target elements (i.e. different target elements are irradiated in succession).

A development provides that the substrate arrangement encloses the respective target element at least in sections. This can be done by receiving a wire-shaped target element in a receiving structure (for example in a groove) as described above and covering this receiving structure with a further element of the substrate arrangement. To put it more generally, the respective target element can be sandwiched between individual substrate elements of the substrate arrangement.

According to the invention, the substrate arrangement comprises a first and a second substrate element, which receive at least a section of the respective target element between them. In this case, the substrate elements can preferably be pressed against one another, for example by means of mechanical fastening or clamping elements or by a heat dissipation element or heat dissipation arrangement explained below. The substrate elements can each be configured in the form of a block and/or configured in such a way that the respective target element bears against them over the entire surface (for example by means of at least one essentially complete base or top surface against them). In one variant, the substrate elements extend along the entire length of the respective target element in the depth direction.

A further development provides that the substrate arrangement is accommodated in a heat dissipation element or in a heat dissipation arrangement which is/is preferably connected or can be connected to a cooling device. The cooling device can be provided externally to the target and can be part of a radiation source explained below, for example. The heat dissipation element or the heat dissipation arrangement can be designed in the form of a block or tube and/or can comprise a receiving section for the substrate arrangement. Additionally or alternatively, the heat dissipation element or the heat dissipation 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 dissipation element or the heat dissipation arrangement can be set up to hold the substrate elements together and/or to press them against one another, e.g. by exerting a pressing or compressive force. In general, a contact between the heat dissipating element (or the heat dissipating arrangement) and the substrate arrangement can be provided, at least in sections, in order to enable good heat transfer to the heat dissipating element or the heat dissipating arrangement. The heat dissipation element or the heat dissipation arrangement can comprise a suitable connection area for connection to the cooling device. Additionally or alternatively, the heat dissipation element or the heat dissipation arrangement can comprise at least one cooling channel into which a coolant can be introduced.

The substrate arrangement can also be connected or connectable to a cooling device. For example, the substrate arrangement can also include a cooling channel and/or a receiving area in which a cooled line of the cooling device can be received. In one variant, the substrate arrangement is flooded and/or washed at least in sections with a coolant from the cooling device.

According to one embodiment, the target has a substrate arrangement which comprises diamond or a diamond-containing material and/or the target has a target element which comprises tungsten and/or the heat dissipation element or the heat dissipation arrangement comprises copper.

In the area of the end face, areas of the respective target element lying away from the exposed side face and in particular the side face of the substrate arrangement can be covered with a layer of material. The material of this layer can be selected in such a way that charging of electrons in the substrate arrangement is essentially suppressed or at least limited. In this way, the generation of an opposing electric field to the electron beam can be avoided. 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 also proposed in which tungsten particles are introduced into a light metal matrix. When such a composition cools down, the tungsten particles can be deposited on an underside of the target. The particle density should be selected in such a way that the particles make up approx. 10% of the underside area. This underside can then be irradiated with an electron beam to generate X-rays. However, the melting point of the light metal matrix can limit the beam power of the electron beam that can be used.

The invention further relates to a radiation source for generating invasive electromagnetic radiation, comprising a target according to one of the preceding aspects; a particle beam source configured to direct a particle beam onto the target; and a positioning device configured to variably align the target and the electron beam relative to one another such that the surface area of the target onto which the particle beam is directed can be varied. The particle beam can in turn include electrons. The particle beam source can include a filament for emitting the electrons. The particle beam and the target can, for example, be rotated relative to one another by the positioning device, for example about an axis running perpendicularly to the particle beam. In one variant, the target can be rotated relative to the particle beam, with the axis of rotation in turn being able to run orthogonally to the particle beam.

By means of the positioning device, the particle beam can be applied to different surface areas of the exposed side surface of the respective Target elements are directed. In the case of a constant thickness of the respective target element, this can be used to compensate for local wear (ie the particle beam can be directed to a section that has not yet been worn, if required). In the case of a varying thickness (for example in the case of a trapezoidal side surface of the respective target element), the focal spot size can also be varied by means of the positioning device.

• - Richten eines Teilchenstrahls auf einen ersten Oberflächenbereich der Stirnfläche des Targets;
• - Verändern einer Relativausrichtung von dem Target und dem Teilchenstrahl derart, dass der Teilchenstrahl auf einen zweiten Oberflächenbereich der Stirnfläche des Targets gerichtet ist;

wobei der erste und der zweite Oberflächenbereich der Stirnfläche unterschiedlich dicke Bereiche von freiliegenden Seitenflächen eines oder mehrerer Targetelemente aufweisen. Die Schrittfolge ist dabei zeitlich variierbar. Es versteht sich z.B., dass die letzten beiden Schritte auch in umgekehrter Reihenfolge und/oder zeitlich überlappend ausführbar sind.The invention also relates to the use of a radiation source of the type described above, comprising the steps:

• - directing a particle beam onto a first surface region of the front face of the target;
• - changing a relative orientation of the target and the particle beam such that the particle beam is directed onto a second surface area of the end face of the target;

wherein the first and the second surface area of the end face have areas of uncovered side faces of one or more target elements of different thicknesses. The sequence of steps can be varied over time. It goes without saying, for example, that the last two steps can also be carried out in reverse order and/or with a time overlap.

In the case of only one target element (which is not covered by the claims), the regions of different thickness can be defined by a trapezoidal shape of an exposed side surface of the target element. In the case of several target elements, as provided according to the invention, these can each have different thicknesses and thus each individually define one of the differently thick areas within the end face of the target. This can be achieved, for example, by the target comprising several wire-shaped target elements with different diameters from one another.

The use may generally include any further step and feature to provide any 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 any heat dissipation element or a heat dissipation arrangement.

• - wird wenigstens eine Mehrzahl von Targetelementen bereitgestellt, die dazu eingerichtet sind, bei einer Bestrahlung mit Teilchen eine invasive elektromagnetische Strahlung zu erzeugen,
• - weisen die Targetelemente jeweils eine Umfangsfläche auf, welche einen ersten Teil der Außenoberfläche des jeweiligen Targetelements bildet,
• - werden die Umfangsflächen mit einer Substratanordnung zur Ableitung von Wärme aus einem jeweiligen Targetelement in Kontakt gebracht,
• - wird die Außenoberfläche jedes Targetelements außerdem durch eine Seitenfläche jedes Targetelements gebildet, wobei eine Erstreckung der Seitenfläche eine Dicke jedes Targetelements definiert und wobei eine Umfangslinie der jeweiligen Seitenfläche eine Randlinie der jeweiligen Umfangsfläche bildet
• - wird die Seitenfläche jedes Targetelements zur Bestrahlung mit den Teilchen freiliegend angeordnet und bildet einen Teil der Stirnfläche des Targets,

wobei die Targetelemente unterschiedliche Dicken aufweisen und die freigelegten Seitenflächen dieser Targetelemente entlang einer gemeinsamen Linie angeordnet sind.The invention also 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. According to the procedure

• - at least one plurality of target elements is provided, which are set up to generate invasive electromagnetic radiation when irradiated with particles,
• - the target elements each have a peripheral surface which forms a first part of the outer surface of the respective target element,
• - the peripheral surfaces are brought into contact with a substrate arrangement for dissipating heat from a respective target element,
• - the outer surface of each target element is also formed by a side surface of each target element, an extent of the side surface defining a thickness of each target element and a perimeter of the respective side surface forming an edge line of the respective perimeter surface
• - the side surface of each target element is exposed for irradiation with the particles and forms part of the front surface of the target,

wherein the target elements have different thicknesses and the exposed side surfaces of these target elements are arranged along a common line.

Features of configurations of the method result from the description of configurations of the target.

Embodiments of the invention are explained below with reference to the accompanying schematic figures. Features that match in their type and function can be provided with the same reference symbols across embodiments.

• 1 schematisch eine Draufsicht auf eine erfindungsgemäße Strahlungsquelle, umfassend ein erfindungsgemäßes Target;
• 2 eine perspektivische Einzeldarstellung eines Targets gemäß einer ersten nicht erfindungsgemäßen Ausführungsform insbesondere zur prinzipiellen, aber nicht erfindungsgemäßen Verwendung in der Strahlungsquelle aus 1;
• 2a eine perspektivische schematische Darstellung eines Targetelements gemäß der in 2 gezeigten Ausführungsform;
• 3 eine Vorderansicht eines Targets gemäß einer zweiten nicht erfindungsgemäßen Ausführungsform insbesondere zur prinzipiellen, aber nicht erfindungsgemäßen Verwendung in der Strahlungsquelle aus 1;
• 4a, 4b schematische Ansichten zum Erläutern einer Brennfleckbegrenzung bei einem Target gemäß Stand der Technik (4a) und bei einem nicht erfindungsgemäßen Target (4b);
• 5 eine Vorderansicht eines Targets gemäß einer dritten nicht erfindungsgemäßen Ausführungsform zur prinzipiellen, aber nicht erfindungsgemäßen Verwendung in der Strahlungsquelle aus 1; und
• 6 eine Vorderansicht eines Targets gemäß einer erfindungsgemäßen vierten Ausführungsform zur erfindungsgemäßen Verwendung in der Strahlungsquelle aus 1.

They represent:

• 1 schematically a plan view of a radiation source according to the invention, comprising a target according to the invention;
• 2 a perspective individual representation of a target according to a first embodiment not according to the invention, in particular for use in principle but not according to the invention in the radiation source 1 ;
• 2a a perspective schematic representation of a target element according to in 2 embodiment shown;
• 3 a front view of a target according to a second embodiment not according to the invention, in particular for the principle, but non-inventive use in the radiation source 1 ;
• 4a , 4b schematic views to explain a focal spot limitation in a target according to the prior art ( 4a) and with a target not according to the invention ( 4b) ;
• 5 a front view of a target according to a third embodiment not according to the invention for use in principle but not according to the invention in the radiation source 1 ; and
• 6 a front view of a target according to a fourth embodiment according to the invention for use in the radiation source according to the invention 1 .

In 1 a plan view of a radiation source 1 according to the invention is shown, which comprises a target 10 according to the invention and with which a method according to the invention can be carried out.

The radiation source 1 comprises a schematically indicated electron beam source 12. The electron beam source 12 forms a particle beam source for emitting electrons. The electron beam source 12 is set up to emit particles in the form of electrons along a particle beam axis A and direct them onto the target 10 . Various coils for aligning and focusing the electron beam are positioned along the particle beam axis A. To put it more precisely, starting from the electron beam source 12 and viewed in the direction of the target 10, first and second beam deflection units 14, 16 are provided, with which the alignment of the beam axis A per se can be varied. A focus coil 18 is also provided, which includes an aperture 20 and with which a focus plane of the electron beam can be adjusted. In a known manner, this focal plane can be positioned in the area of the target 10 or slightly in front of or behind it. Also not shown is that at least in the area of the beam deflection units 14, 16 and the focus coil 18, a copper tube can be provided which surrounds the beam axis A.

The target 10 is in 1 also shown in plan view. An extension area 21, in which the target elements are arranged in particular according to one of the following embodiments, is indicated by dashed lines. An extension of the depth T of the target is also marked. This generally coincides with a longitudinal extension of the target elements explained below.

The target 10 has an end face 22 which faces the electron beam and is slightly convex. As discussed below, this face 22 is also inclined to the electron beam and relative to the plane of the page. If the electron beam hits the end face 22 and penetrates into the material of the target 10 and is decelerated, whereupon X-rays are emitted. A useful X-ray beam cone emerges along an axis SA through a diaphragm 24 into the environment and, after passing through an object, falls onto a detector device (not shown) in order to generate a through-radiation image of the object.

The target 10 is also coupled to a positioning device 26 (or adjustment mechanism). The positioning device 26 enables the target 10 to be rotated about an axis V which is perpendicular to the plane of the page. Consequently, the end face 22 of the target 10 can also be rotated relative to the electron beam. As from the view of 1 can be deduced, for example if the alignment of the electron beam axis A remains the same, the electron beam can thus be directed at different areas of the end face 22 of the target 10 and, in particular, be moved along a line along the end face 22 (e.g. in 1 from top left to bottom right or vice versa). As will be explained in more detail below, such a positioning option makes sense in order to react to local wear (eg burning off) of the target 10 . It is also possible in certain embodiments to vary the focal spot size. Additionally or alternatively, it is also possible according to the invention to achieve a slight change in the position of the focal spot by changing the alignment of the electron beam axis A (e.g. by means of the corresponding beam deflection units 14, 16 and/or by means of the focus coil 18 as part of a so-called beam adjustment).

As from the representation of 1 can also be derived, the curved end face 22 of the target 10 ensures that a constant distance between the end face 22 and the electron beam source 12 is maintained in the direction of the electron beam axis A even when rotating about the axis V. The consequence of this is that the arrangement of the end face 22 relative to the focal plane of the electron beam does not change significantly and the focal spot size also remains essentially constant.

In 2 FIG. 12 is a schematic perspective detail view of a target 10 for use in the radiation source 1 in particular 1 shown. The target 10 is designed according to a first embodiment. It comprises a layered target element 20, in the case of an electron beam an anode element, which has tungsten. The target element 20 is designed to be irradiated with electrons to emit bremsstrahlung in the form of X-rays.

The target element 20 is accommodated in a substrate arrangement 28 which consists of diamond produced, for example, by means of a CVD (Chemical Vapor Deposition) method. The substrate arrangement 28 comprises a first substrate element 30 and a second substrate element 32. In the representation of 2 The upper and lower surfaces of the target element 20 are each in mechanical contact with the substrate arrangement 28, preferably in full-area contact. Therefore, the target element 20 between the two substrate elements 30, 32 is arranged. In a specific embodiment, the target element 20 is applied by depositing its material on the first substrate element 30 and the second substrate element 32 is pressed against the surface of the target element 20 that is at the top in the illustration. The deposition of the material of the target element 20 has the advantage that a good thermally conductive connection to the first substrate element 30 can thereby be created. In addition, the deposition of material is well suited to create a layered target element. After the material has been deposited, the shape of the deposited material can still be changed, for example to 3 generate target element shown.

The substrate arrangement 28 itself is accommodated in a heat dissipation arrangement 34 which is in turn formed in two parts and is made, for example, of copper. More precisely, the heat dissipation arrangement 34 encloses the substrate arrangement 28 and bears against the substrate arrangement 28 over a large area on the largest outer surfaces thereof. At least one cooling channel 36 is also provided in the heat dissipation arrangement 34, through which a coolant flows for dissipating heat. The cooling channel 36 is connected to a cooling device (not shown) of the radiation source 1 .

In 2 and in the following figures, the target 10 is not shown with a curved end face 22 but with a planar end face 22 due to the simpler representation. This applies analogously to the target element 20 and the substrate arrangement 28. The curved end face 22 is advantageous for the reasons mentioned above, although the invention is not limited thereto, so that the end face 22 can also be flat.

The basic structure of the target 10 explained above is explained in more detail below. First you can see in 2 that in the end face 22 facing the electron beam, the substrate arrangement 28 and also the target element 20 are each uncovered and thus exposed. It is not shown that the in 2 The corresponding front surfaces of the substrate elements 30, 32 shown can also each be shielded with a suitable layer of material (for example made of carbon) in order to prevent the creation of an opposing electric field when irradiated with the electron beam.

The target element 20 is formed in layers. In the exemplary embodiment shown, the layer thickness D is constant. Furthermore, the layer thickness D is selected 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 can be seen that a respective thickness C of the substrate elements 30, 32 is the layer thickness D of the target element 20 by a multiple, e.g. B. at least five times and preferably at least ten times. All of the thickness dimensions C, D explained above run perpendicularly to the depth direction in which the target element extends with a depth T. If the target 10 is in an arrangement as in 1 is used, the electron beam axis A impinges on the exposed end face of the target element 20 inclined or angled to the depth direction.

Furthermore, in 2 indicated by dashed lines that the target element 20 extends with a length L into the target 10 . This length L corresponds to a depth T of the target 10 explained above (see FIG 1 ). The length L is preferably at least 10 μm, at least 20 μm or at least 40 μm, particularly preferably at least 100 μm. In practice, the length can be 200 μm, for example. Alternatively or additionally, the length L can be greater than the layer thickness D by a factor of at least 3 or 5, preferably by a factor of at least 10.

The width B is preferably at least 1 mm or at least 2 mm, more preferably at least 4 mm and in practice can be 5 mm, for example. The width B can therefore be greater than the layer thickness D by at least a factor of 20, 50 or 100. The size of a focal spot can thus be limited in the direction of the layer thickness D, while in the direction of the width B a large area for the focal spot, i . H. for generating X-rays. The size of the focal spot in the width B direction can be significantly smaller than the width B at any time. For example, the size of the focal spot in the width B direction can be larger than 10 μm or 20 μm and/or smaller than 200 μm or 100 µm and e.g. B. be 60 microns. The width B can, for example, be at least a factor of 5, 10 or 50 larger than the size of the focal spot in the direction of the width B.

The target element 20 is consequently accommodated in the substrate arrangement 28 along its entire length L, the substrate arrangement 28 also being accommodated in the heat dissipation arrangement 34 along its entire length. “Incorporated” means in particular that the surfaces of the adjacent layers of the target element and the substrate arrangement are in contact with one another over their entire surface. The resulting large-area contact areas enable a comprehensive heat exchange between these elements and in particular a heat dissipation from the target element 20 into the substrate arrangement 28 and from there into the heat dissipation arrangement 34.

In the exemplary embodiment, the target element 20 also has an essentially rectangular outline or, to put it another way, an essentially rectangular base area. This comprises two shorter sides 2 and two longer sides 3, each of which runs parallel, like the enlarged representation of only the target element 20 in 2a indicates. One of the shorter sides 2, namely the in 2 front and in 2a left front side, has an exposed side surface 38 arranged within the end face 22 of the target 10 and exposed for irradiation with electrons or other particles. The side surface 38 defines the thickness D and the comparatively larger width B of the layered target element 20.

Due to the layered design of the target element 20, the latter can be cuboid (as in 2a shown) or be prismatic. The uncovered side surface 38 and a further side surface 38a lying opposite it can consequently be understood as a cover surface and a base surface of this cuboid or prism. These side surfaces 38, 38a border on outer surfaces 39, 39a of the target element 20, which in the representation of 2a lie on an upper side and on an underside of the target element 20, cf. 2a . A side surface 37 and a side surface 37a opposite thereto run perpendicularly to the outer surfaces 39, 39a and to the exposed side surface 38 and the side surface 38a opposite thereto. The side surfaces 37, 37a and the outer surfaces 39, 39a together form a closed peripheral surface which encloses the material volume of the target element 20 in the sense of a cavity with a rectangular cross section. An edge line R of the peripheral surface that is closed in itself on one side forms a peripheral line of the exposed side surface 38. The edge line R and the peripheral line are therefore identical. If the target element 20 is designed as a cuboid, the outer surface 39 on the upper side and the outer surface 39a on the lower side run orthogonally to the end face 22 of the target 10. The surface area of the peripheral surface is preferably by a factor of at least 10, preferably by a factor of 50 or more preferably by a factor of 100 larger than the surface area of the exposed side surface 38.

The consequence of this is that a comparatively small proportion of the material of the target element 20 is exposed for irradiation with the electrons and that, on the other hand, a correspondingly large proportion of material adjoins and remains on the substrate material of the substrate arrangement 28 in order to dissipate heat directly into the substrate arrangement 28 and prevent any burning of the Target element 20 to compensate.

This relationship also becomes clear from a closer look at the substrate arrangement 28. As mentioned, the substrate elements 30, 32 of the substrate arrangement 28 are essentially block-shaped and are designed with a greater thickness C compared to the target element 20. FIG. You can see that an in 2 first lower substrate element 30 rests against an underside of target element 20 , while a second upper substrate element 32 rests against an upper side of target element 20 . The substrate elements 30 , 32 each extend into the target 10 with a length analogous to that of the target element 20 . The consequence of this is that the underside of the target element 20 rests against the substrate element 30 over its entire surface and the upper side of the target element 20 rests against the substrate element 32 over its entire surface. A focal spot position on the side surface 38 and a direct dissipation of the heat into the first substrate element 30 and second substrate element 32 are thus achieved.

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 a previously known solder material which comprises, for example, copper, silver, gold or tin and nickel. The remaining substrate element 30, 32 can then be pressed onto the remaining upper or lower side of the target element 20 in each case. A corresponding pressing force can be applied via mechanical fastening or clamping means that are not shown. These can also be provided to clamp the two parts of the two-part heat dissipation arrangement 34 to one another, with a corresponding contact pressure being able to be transmitted from the heat dissipation 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 dissipation arrangement 34 and also the exposed side surface 38 of the target element 20 with can align with each other, but this is not absolutely necessary. The end face 22 of the target 10 can thus have a substantially smooth surface, with an in 2 not separately shown curvature of the entire end face 22 or only the side surface 38 according to the plan view 1 can be provided.

As explained, the target element 20 is formed with a constant thickness D, which is shown in FIG 2 and the 2a a height of the side surface 38 corresponds. In particular, this thickness D is along a width B (see 2a) of the side surface 38 is constant, this width B being transverse to the length L of the base surface of the target element 20. A second embodiment of a target 10 that differs from this is described below with reference to FIG 3 explained. The basic structure of this target 10 essentially corresponds to that of FIG 2 , except as explained below.

3 12 shows a front view of the end face 22 of the target 10 according to a second embodiment. The end face 22 can be analogous to the top view 1 be convexly curved overall or only in the area of the exposed side surface of the target element. Furthermore, it can be designed with a flat surface and again comprises corresponding end faces of the heat dissipation arrangement 34, which is again divided into two, of the two substrate elements 30, 32, which sandwich a target element 20, and an exposed side surface 38 of the target element 20. The target element 20 is again layered and in plan view (corresponding to 1 ) rectangular (not recognizable in 3 ). The exposed side surface 38 in turn forms a shorter side of this rectangle.

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, this varies so that a cross-sectional shape of the target element 20 and thus a shape of the exposed side surface 38, as in 3 recognizable, trapezoidal. More precisely, one recognizes in 3 that the layer thickness D increases from left to right and thus along the width B of the exposed side surface 38 and even increases continuously or linearly in the embodiment shown. Depending on which section of the exposed side surface 38 the electron beam is directed onto, it hits an area of the target element 20 of different thickness. This interaction area or area of impact of the electron beam on the target element 20 is also referred to as the focal spot. Thus, by directing the electron beam at different portions of the exposed side surface 38, the focal spot size can be varied, as will be explained in more detail below. The changing of the orientation of the electron beam relative to the target 10 can in turn be carried out by means of the positioning device 26 1 take place.

Based on 4a and 4b the generation of X-ray radiation is explained in more detail below. 4a and 4b contain analog representations, but in 4a a target 10 according to the prior art and in 4b a target according to the second embodiment 3 is used.

Referring first to 4a is in the left pane of the 4a a plan view of part of the target 10 is shown, on the end face 22 of which an electron beam E with, for example, a circular cross-section impinges. The cross section of the electron beam E and also the cross section of the resulting X-ray beam, the formation of which will be described below, are shown rotated in the plane of the figure. In the right pane of 4a a left side view along AA is shown.

In this embodiment according to the prior art, the end face 22 is formed over its entire surface by an anode material (i.e. target material suitable for generating invasive radiation). This can be achieved, for example, in that a corresponding target element 20 is formed as a layer, but this layer completely covers an underlying substrate end face of the target 10 and is applied flatly to it.

The electron beam E impinges on the inclined end face 22 in an elliptical impact or interaction area, so that the right-hand side in 4a shown elliptical focal spot 40 is formed. As a result of the interaction of the anode material and the electron beam E, an X-ray beam S1 is emitted with a cross-section that is also elliptical and completely filled (see Fig 4a , lower area).

The representation in 4b shows in its left area a plan view of a target 10 according to FIG 3 . 4b shows in an analogous way how 4a the impingement of an electron beam E with a circular cross-section on an inclined end face 22 of the target 10. In this case, too, the impingement area of the electron beam E on the target 10 is elliptical due to the inclination of the end face 22. Since the material of the target element absorbs the impinging electron energy with clearly higher efficiency than the substrate elements 30, 32 converts into X-rays, X-rays are emitted in the area of the focal spot 40 only in the zone of the target element. From the elliptical Focal spot 40 is therefore cut off from the lateral edge areas, so that only a trapezoidal sub-area remains as a focal spot for the generation of X-rays. The radiation in the elliptical area of impact thus generates an X-ray radiation only in a trapezoidal sub-area of the area of impact, since the side surface 38 of the target element 20 is exposed only in the trapezoidal sub-area. In the right area of 4b FIG. 14 is a front view of the target 10 along arrows BB in the left portion of FIG 4b shown. This view corresponds to the front view of the embodiment according to FIG 3 . The focal spot 40 is thus limited in one dimension (namely in the dimension of the layer thickness D) by the layer thickness D, which in this embodiment is not constant in width. This is advantageous since the size of the resulting focal spot 40 can be adjusted by directing the electron beam onto regions of different thicknesses of the exposed side surface 38 of the target element 20 . An X-ray beam S2 is emitted from the target element 20 and has a cross-sectional area which is smaller than the cross-sectional area of the X-ray beam S1 according to the prior art, cf. 4a . This is advantageous because a higher resolution can be achieved (cf. 4b , left panel).

In summary, it becomes clear from 4b that with the target a relatively small cross-sectional area of the emitted x-ray radiation S2 can be achieved. This is achieved by irradiating the exposed side surface 38 of the target element 20 according to the embodiment in FIG 4b , instead of irradiating a target element 20 according to the prior art, in which there is no delimitation of the focal spot 40 in the area of incidence of the irradiation (see 4a) . However, since a comparatively large volume of material is available via the layer-like extension of the target element 20 into the target 10 explained above, heat that is produced can be transported away from the target element 20 with sufficient power. The electron beam E therefore does not have to be expanded significantly or even partially dimmed in order to avoid damage to the target element 20 . As a result, a small cross-sectional area of the emitted X-ray radiation is made possible while maintaining a high power density.

In 5 and 6 further embodiments of a target 10 for use in a radiation source 1 are shown 1 shown. The illustrations each show a front view of an end face area of the target 10, although an outer heat dissipation element or an outer heat dissipation arrangement 34 is not shown in each case, but is provided in principle. Instead, a substrate arrangement 28 with two block-shaped substrate elements 30, 32 is again shown. These each take at least one target element 20 between them.

The target elements 20 are wire-shaped and designed with a circular cross-section and extend analogously to the layer-like design according to FIG 2 shown embodiment along a respective longitudinal axis not shown separately in the target 10 inside. A sufficient volume of material is again made available to compensate for wear and to ensure high heat dissipation from the focal point directly into the substrate elements 30, 32. As in 5 shown, the exposed side surface 38 of a target element 20 is thus also circular. A diameter of the wire-shaped target element 20 consequently also defines a thickness D of the target element 20 and the exposed side surface 38 which is available for irradiation by electrons.

In the variant of 5 only one target element 20 is provided. This is accommodated in a receiving structure 42 in the form of a groove with a rectangular cross section open on one side. However, other receiving structures 42 and in particular cross-sectional shapes are also conceivable. For example, a U-shaped or a V-shaped groove can also be provided. The groove is formed in the lower first substrate member 30, while the in 5 shown upper second substrate element 32 closes the open side of the groove. For this purpose, the substrate elements 30, 32 are pressed against one another analogously to the above embodiments.

A focal spot size is thus decisively determined via the thickness D of the wire-shaped target element 20 when an electron beam impinges on the exposed side surface 38 . The thickness D can in turn be selected in such a way that small spot sizes or cross-sectional areas of the emitted x-ray radiation S2 can be achieved. If, for example, 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) limits the resulting focal spot 40 accordingly, which also limits the spot size of the emitted X-ray radiation S2 (cf. 4b) . If required, target material can be tracked via the additional material volume of the wire-shaped target element 20 running into the plane of the page.

Although in 5 only a single target element 20 is shown, a plurality of wire-shaped target elements 20 can also be provided, preferably within the end face 22 along a common line and preferably parallel are arranged to each other. The target elements 20 can be designed with the same thickness D, so that when one of the target elements 20 wears out, it is possible to switch to another, not yet worn out target element 20 by realigning the electron beam and the target 10 (e.g. by means of the positioning device 26 from 1 ).

In 6 On the other hand, an embodiment is shown in which a plurality of wire-shaped target elements 20 with different thicknesses D1, D2 and D3 of their side surfaces 38 are exposed within the end face 22 of a target 10. Depending on which target element 20 the electron beam is aimed at, a different focal spot size and thus a different cross section of the x-ray beam generated can be set. The exposed side surfaces 38 are arranged side by side with their upper outer edge points along an in 6 horizontally extending line are arranged, which is defined by the lower edge of the second substrate element 32. By means of suitable dimensions and/or shapes of the receiving structures, it can alternatively be achieved, for example, that the respective center points of the circular, exposed side surfaces 38 lie on a virtual straight line (not in 6 shown).

Since the focal spot size is decisively determined by the thickness of the target element 20 in the exemplary embodiments shown, the requirements for focusing the electron beam can also be reduced. For example, if the electron beam is not focused with high precision, it tends to affect the efficiency of the radiation source 1 in terms of a ratio of the power of the electron beam source 12 to the x-ray radiation achieved. The focal spot size, on the other hand, remains comparatively stable even with imprecise focusing, so that an essentially constant resolution can be achieved. This can be achieved in that an impingement area of the electron beam E on the target element 20 that is too large or too small due to imprecise focusing has no effect, since the resulting focal spot 40 is already predetermined and limited by the thickness D of the target element 20.

Claims (11)

Target (10) for a radiation source (1) of invasive electromagnetic radiation, having a plurality of target elements (20), which are each set up to generate invasive electromagnetic radiation when irradiated with particles, and each having a substrate arrangement (28) coupled for dissipating heat from a respective target element (20), each target element (20) having a peripheral surface forming a first portion of an outer surface of each target element (20), the outer surface of each target element (20) being further defined by a side surface ( 38) of the respective target element (20), an extension of the side surface (38) defining a thickness (D; D1, D2, D3) of the respective target element (20), a peripheral line of the side surface (38) being an edge line of the peripheral surface forms, wherein the target (10) has an end face (22), as part of which the side faces (38) of the target elements (20) for irradiation are arranged with the particles exposed, and wherein the substrate arrangement (28) is in contact with the peripheral surfaces of the target elements (20), the target elements (20) having different thicknesses (D1, D2, D3) and the exposed side surfaces (38) of the Target elements (20) are arranged along a common line, characterized in that the substrate arrangement (28) has a first substrate element (30) and a second substrate element (32) which receive at least a portion of the respective target elements (20) between them. Target (10) after claim 1 , wherein the peripheral surfaces of the target elements (20) are larger than the respective side surfaces (38). Target (10) after claim 1 or 2 , wherein each target element (20) has a polygonal outline with different side lengths and wherein the side surfaces (38) each define a side of this outline that does not have the longest side length. Target (10) according to one of the preceding claims, wherein the target elements (20) are each formed in layers and have a greater width (B) compared to the thickness (D), with a total length of the respective peripheral line passing through the thickness (D) and through the Width (B) is defined, wherein the substrate arrangement in the direction of thickness (D) opposite sides of the peripheral surfaces is in contact with them. Target (10) after claim 4 , wherein the thickness (D) of the respective layer-like target element (20) on the side surface (38) increases as it extends in the direction of the width (B). Target (10) after one of Claims 1 until 3 , wherein the target elements (20) are each cylindrical and wherein the respective side surfaces (38) form an elliptical or circular end surface of a respective target element (20). Target (10) according to one of the preceding claims, wherein the substrate arrangement (28) encloses the target elements (20) at least in sections. Target (10) according to one of the preceding claims, wherein the substrate arrangement (28) is accommodated in a heat dissipation element or heat dissipation arrangement (34) which is connected or connectable to a cooling device. Target (10) according to one of the preceding claims, wherein the substrate arrangement (28) comprises diamond or a diamond-containing material and/or wherein the target elements (20) comprise tungsten. Radiation source (1) for generating invasive electromagnetic radiation, comprising: - a target (10) according to any one of the preceding claims; - A particle beam source (12) which is set up to radiate a particle beam onto the target (10); and - A positioning device (26) which is set up to align the target (10) and the particle beam variably relative to one another, so that the surface area of the target (10) onto which the particle beam is directed can be varied. Method for producing a target (10) for a radiation source (1) of invasive electromagnetic radiation, wherein: - a plurality of target elements (20) are provided, which are each set up to generate invasive electromagnetic radiation when irradiated with particles, - the target elements (20) each have a peripheral surface which forms a first part of an outer surface of the respective target element (20), - the peripheral surfaces are brought into contact with a substrate arrangement (28) for dissipating heat from a respective target element (20), - the outer surface of each target element (20) is also formed by a side surface (38) of each target element (20), an extension of the side surface (38) defining a thickness (D) of each target element (20) and a peripheral line of the respective side surface (38 ) forms an edge line (R) of the respective peripheral surface, - the side surface (38) of each target element (20) is exposed for irradiation with the particles and forms part of the end face (22) of the target (10), the target elements (20) having different thicknesses (D1, D2, D3) and the exposed side faces (38) of these target elements (20 ) are arranged along a common line, characterized in that the substrate arrangement (28) comprises a first substrate element (30) and a second substrate element (32) which receive at least a portion of the respective target elements (20) between them.

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