WO2009098027A1

WO2009098027A1 - X-ray target

Info

Publication number: WO2009098027A1
Application number: PCT/EP2009/000706
Authority: WO
Inventors: Frank Sukowski; Norman Uhlmann; Gisela Anton; Anja Loehr; Randolf Hank
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2008-02-04
Filing date: 2009-02-03
Publication date: 2009-08-13
Also published as: DE102008007413A1

Abstract

An X-ray target for producing X-rays (110) in a region of incidence (M) of an electron beam (120) onto the X-ray target comprises an X-ray source layer (130) and a substrate (140). The X-ray source layer (130) comprises a high atomic number material and the substrate (140) comprises a low atomic number material. The X-ray source layer (130) is formed on the substrate (140) and the substrate (140) has a layer thickness (D) in the direction of a surface normal (150) in the region of incidence (M) of at least 1 cm.

Description

Röntgentargβt

description

The present invention relates to an X-ray source for generating X-ray radiation at an impact region of an electron beam on the X-ray target, and more particularly to a reflection X-ray target with a thin X-ray source layer of high atomic number and a substrate of low atomic number.

X-rays are not only of great importance in medical technology, but are also used in material testing, eg in As regards the detection of defects in materials, a diverse application. X-ray radiation can be generated, for example, by means of an electron beam which is shot at a target, so that the incident electrons are strongly decelerated by emitting a Bremsstrahlung and deliver their remaining energy in the form of heat to the target. The Bremsstrahlung has a continuous spectrum ranging from a low energy range to a high energy range. The high radiation energy is caused by the fact that the electrons are abruptly decelerated in the sudden impact on the target within a very short range. The braking effect is achieved by interaction of the electrons with the atoms with the emission of X-rays (or generally of photons with the corresponding energy).

The angle of the outgoing X-ray radiation depends on the one hand on the energy of the radiating electron and on the angle at which the electrons hit the X-ray target. It is thereby possible to operate X-ray targets both as a transmission X-ray target and as a reflection X-ray target. For transmission targets, the X-radiation, which is reflected in motion In the case of reflection X-ray targets, the X-ray radiation which propagates from the surface on which the electron beam impinges is used (in the direction of reflection).

Since the incident electrons release their energy as bremsstrahlung (X-radiation) and in the form of elastic and inelastic collisions to the material and heat up the material, the X-ray targets are usually constructed in a two-layer system. In a first layer, the electron beam is decelerated while emitting the X-ray radiation and in the second layer, the conversion of the remaining kinetic energy of the electrons into heat energy, which is then derived as efficiently as possible.

Layered-target X-ray tubes are described in the prior art in DE 27 29 833, in US 20 90 636, in US 3 894 239, EP 0 584 871, DE 10 2005 018 342 A1 and EP 0 432 568. The x-ray radiation in the transmission direction is used in the x-ray tubes or x-ray targets known from these publications, with the x-ray radiation being used both in the transmission direction and in the reflection direction in the case of the document EP 0 432 568.

The operation of the X-ray target in the transmission direction, ie the use of X-radiation propagating in the direction of the electron beam, is disadvantageous in that the X-ray target may have only a (limited) layer thickness, otherwise the X-ray radiation will be completely absorbed by the target would become. However, the limited upper layer thickness simultaneously has a greatly limited heat-absorbing capacity and heat dissipation capability. This leads to a considerable heating of the X-ray target. However, it is important, especially when producing a high-intensity X-ray radiation, which can be generated, for example, by a high-intensity electron beam which impinges on the X-ray tube, that the additionally generated heat quantity be efficiently diverted so that the material of the X-ray target is only limited is exposed to thermal stress. Since the electrons release their kinetic energy predominantly into heat and emit only a small percentage range (for example about 1%) in the form of bremsstrahlung, a large amount of heat is generated during the operation of the x-ray tube. Thus, if an increase in the power of the X-radiation is achieved by an increase in the power of the electron beam, this simultaneously leads to a significant increase in the amount of heat to be derived from the X-ray target or the X-ray tube. On the other hand, if the x-ray target is to be operated in the transmission direction, as already mentioned above, it must have only a limited thickness (maximum layer thickness) so that the x-ray radiation is not or hardly absorbed by the x-ray target. Thus, these conventional X-ray targets always require a compromise with respect to the dimensioning of the X-ray target.

Starting from this prior art, the present invention has the object to provide an X-ray target, which allows a large-volume distribution and thus an efficient dissipation of the heat caused by the electron radiation.

This object is achieved by an X-ray target according to claim 1, a use according to claim 12, an X-ray tube according to claim 13 and a method of manufacturing according to claim 15.

The present invention is based on the finding to provide an X-ray target by a substrate and an X-ray source layer formed thereon, wherein the Substrate has a minimum thickness. The minimum thickness is chosen to efficiently dissipate the amount of heat caused by the electron beam incident on the X-ray target. The minimum layer thickness of the substrate may be at least 1 cm or at least 2 cm measured along the surface normal to the surface on which the electron beam impinges. Furthermore, the present invention is based on the finding that the X-ray target thus created is used in the reflection mode and the radiation in a small target angle (the 90 ° complementary angle between the surface normal of the X-ray source layer and the emitted X-radiation).

The subject of the present invention thus comprises an X-ray target for generating X-ray radiation in an incident region of an electron beam onto the X-ray target. The X-ray target comprises an X-ray source layer comprising a high atomic number material and a substrate having a low atomic number material, wherein the high atomic number of the X-ray source layer is at least twice the low atomic number of the substrate. The x-ray source layer is formed on the substrate, and the substrate has a thickness in the direction of a surface normal of an interface between the x-ray source layer and the substrate at the impact region of at least 1 cm. The substrate has a first major surface on which the x-ray source layer is formed and a second major surface on the side opposite the x-ray source layer, wherein surface normals of the first and second major surfaces intersect at an inclination angle and the inclination angle is between 0 ° and 45 ° ,

In its simplest form, the x-ray source layer is formed directly on the substrate without the need for additional intermediate layers. Such a 2-layer X-ray target can be optimized so that Excitation energies of more than 30 keV or a range between 30 keV and 100 keV in the direction of reflection as many photons as possible (as intense as possible X-radiation) at a thermal limit load of the target (Röntgentar- get) are generated. The diameter of the optical focal spot is for example between 1 .mu.m and 1000 .mu.m or between 50 .mu.m and 500 .mu.m or between 100 .mu.m and 300 .mu.m.

The x-ray source layer (upper layer on which the electron beam strikes) has, for example, tungsten as a material of a higher atomic number. In this layer, the X-radiation is generated, while in the lower layer, the substrate, the electrons release their residual energy as heat to the solid.

The physical background to using a layered target is the relationship between the type of interactions over which the electrons in the electron beam lose their energy into a material, the interaction in particular being dependent on the kinetic energy of the electrons E and the atomic number Z of the electron Material depends. For the energy loss by Bremsstrahlung generally the following qualitative context applies (numerical factors are omitted):

_Breras or Z ^• E In E

The remaining energy, d. H. the energy that the electrons do not emit in the form of photons (bremsstrahlung) is converted as heat in the target material. The highest possible emission of X-radiation is thus achieved with the highest possible atomic number of the target material and with a high kinetic energy of the electrons.

In order to achieve the most efficient implementation of the energy of the electron beam in X-rays, it is very important to choose the material of the x-ray source layer as well as the material of the substrate suitable. Criteria for the choice of material for the x-ray source layer are, for example:

High atomic number,

High melting point and

High thermal conductivity.

However, the amount of energy that is converted into X-rays is generally very low. For example, even using tungsten as the target (x-ray source layer) and energy for the electron beam of 100 keV, only about 1% of the energy is converted to x-rays, so that the remaining 99% will be converted to thermal energy, and hence the anode, as the the x-ray target in an x-ray tube generally serves to receive the remaining energy of the electron beam and thereby strongly heat. For this reason, increasing the power of the X-radiation by increasing the power of the electron beam is limited (because of the enormous amount of heat additionally produced).

Due to the high atomic number, the (X-ray) beam generation in the X-ray source layer is efficient, but the generated heat is deposited to a very small volume. Accordingly, the thickness of the x-ray source layer is chosen such that electrons which have lost part of their kinetic energy and thus have a low probability of producing further x-ray radiation leave this layer again. The remaining or remaining energy is then deposited in the substrate. The heat-deposition density in the substrate is lower by a factor of 3 to 30 or 5 to 10 compared to the heat-deposit density in the x-ray source layer in the x-ray source layer, which, as stated, reduces the substrate significantly less (the amount of heat becomes larger) volume distributed or derived). This is realized by a small atomic number of the substrate. In addition, the substrate serves to quickly dissipate the heat from the x-ray source layer to a cooling bottom.

Criteria for the choice of material for the substrate are thus:

Low atomic number, high melting point and - high thermal conductivity.

For example, carbon configurations, such as. As graphite or diamond, suitable as materials.

Another object of the present invention is the use of the X-ray target in the reflection mode - instead of in the transmission mode, as used in the prior art described above. The advantage of the reflection mode is that the substrate can in principle be arbitrarily thick in order to absorb as much heat as possible. In addition, efficient cooling mechanisms can be realized on the side of the substrate remote from the electron beam (e.g., cooling bottom, copper plate, etc.).

Furthermore, very small focal spots are possible with larger electric focal spots due to small target angles during reflection. This means that in reflection mode, the electron beam does not need to be focused on a single point, and nevertheless the X-ray radiation can be focussed as far as possible within small angular deviations.

As described above, during operation, the electron beam radiation causes the X-ray target to strongly heat up during operation, with the x-ray source layer becoming significantly warmer than the underlying substrate. In order to protect the X-ray source layer (preventing melting), the X-ray source layer should not be too thick be chosen so that a large proportion of the energy of the electron beam is given in the form of heat to the underlying substrate and the X-ray source layer is essentially the generation of X-rays, but not the conversion of the kinetic energy of the electrons into heat energy. The thickness of the X-ray source layer can be selected, for example, such that the heat input into the X-ray source layer amounts to a maximum of 20% of the total heat deposited in the anode (X-ray target). This means that the large amount of energy that is released into the substrate in the form of heat should be at least 80%.

In order to ensure efficient reflection operation, the X-ray target in embodiments of the present invention, on the one hand, formed wedge-shaped, so that the electron beams impinge on the X-ray target at an acute angle and, secondly, the substrate may be formed on an underlying cooling floor. The cooling floor can, for example, have a copper plate, which can efficiently transport heat.

Embodiments of the present invention will be explained below with reference to the accompanying drawings. Show it:

1 is a cross-sectional view of an X-ray target according to an embodiment of the present invention;

Figs. 2A, B are top views of the X-ray source layer with a labeled electric focal spot;

3 is a cross-sectional view through the X-ray target illustrating the geometric dimensions of the substrate; 4 shows a cross-sectional view through the X-ray target and the cone-shaped X-ray radiation;

5 shows a cross-sectional view through the X-ray target with a large electric focal spot; and

Fig. 6 is a cross-sectional view through an X-ray tube with the X-ray target according to the present invention.

With regard to the following description, it should be noted that in the different embodiments, identical or equivalent functional elements have the same reference numerals and thus the description of these functional elements in the various embodiments are interchangeable.

FIG. 1 shows a cross-sectional view through the X-ray target, wherein X-ray radiation 110 is impinged by an electron beam which impinges on an X-ray source layer 130 at an angle of incidence α and the X-ray source layer is formed on a substrate 140. The angle of incidence α is determined relative to a surface normal 150, the surface normal 150 having been determined at the point of incidence M of the electron radiation 120 on the x-ray source layer 130. The x-ray radiation 110 generated by the electron beam 120 is generated almost uniformly in all directions starting from the impact point M. The used X-radiation 110 forms a cone. The opening angle of the cone is defined by the size of the exit window and the distance of the exit window (or aperture) to the impact point M.

When generating the X-ray radiation, the electrons of the electron beam 120 first penetrate into the X-ray source layer 130, are decelerated there by emitting the Bremsstrahlung, the Bremsstrahlung emitted as X-radiation 110 from the X-ray source layer 130 becomes. The Bremsstrahlung has a continuous spectrum with a high energy X-ray content. The remaining kinetic energy of the electrons is usually released to the substrate 140 in the form of heat. In order to eventually dissipate the electrons that have penetrated the substrate 140, the substrate 140 may further include a terminal (not shown in the figure).

In this case, the substrate 140 is designed in such a way that X-ray radiation 110 is emitted substantially only as reflection beams from the X-ray source layer 130-but not as transmission beams through the substrate 140. The operation of the X-ray target in the reflection mode makes it possible to make the substrate 140 sufficiently thick (in the one-beam direction), so that the heat generated there can be dissipated efficiently. By way of example, the layer thickness D of the substrate 140-measured along the surface normal 150-can have a value which is at least 1 cm or at least 1.5 cm or at least 2 cm.

FIGS. 2A and 2B are plan views of the x-ray source layer 130, with the impact point M of the x-rays 120 shown as a geometric center. However, the impact point M may also deviate from the geometric center of the surface facing the electron beam 120 and be located in a region G. In order to avoid "burn-in" (local melting), it may be advantageous not to focus the electron beam to a point and instead to distribute the electron beam to the region G or a part of the region G, so that a larger electrical focal spot Alternatively, the electron beam may also travel in the region G, so that uniform heating of the region G occurs and not a particular point is heated particularly strongly.

In Fig. 2A, the area G is shown as a circle concentrically arranged around the geometric center M. is. The geometric center M can be formed, for example, by minimizing the sum of the mean square distances to all points on the surface of the x-ray source layer 130. In the simple case of a rectangle or a circle, the geometric center can be determined by the intersection of the diagonals of opposite corner points. It is also possible for the region G to comprise either the entire surface of the x-ray source layer 130 or only part of the x-ray source layer 130. For example, the area G may comprise at least 5% or at most 70% or a value between 20% and 60% of the area of the x-ray source layer 130.

In Fig. 2B, the region G is obtained by simply scaling the surface of the x-ray source layer 130, wherein the surface of the x-ray source layer 130 again has a rectangular (or square) shape. The scaling is effected by a scale factor by which the surface of the x-ray source layer 130 is reduced to the geometric center point M. The scaling factor may be in a range between 1.5 and 10, for example. Other embodiments for the area G are also possible and it may be advantageous to choose the area G as large as possible, so that the x-ray source layer 130 is loaded as evenly as possible by the electron beam.

3 again shows a cross-sectional view through the X-ray target, wherein the region G, on which the electron beam 110 impinges on the X-ray source layer 130, is centered. In the cross-sectional view shown in FIG. 3, the region G thus appears as a line segment between a first boundary point Ma with a first surface normal 150a and a second boundary point Mb with a second surface normal 150b, wherein the surface normals in turn relate to the surface of the x-ray source layer 130. The first and second surface normals 150a and 150b are traversed by the substrate 140 having a first major surface 142 and a second major surface 144, where the x-ray source layer 130 is formed on the first major surface 142.

The first surface normal 150a has a first length Da measured along the first surface normal 150a between the first and second main surfaces 142 and 144. In an analogous manner, the second surface normal 150b has a second length Db for a portion extending within the substrate 140. Thus, in the embodiment shown in FIG. 3, all the surface normals that can be drawn in the region G have distances between the first and second main surfaces 142 and 144 that lie between the first length Da and the second length Db.

In embodiments of the present invention, the described length range of the surface normal is selected such that the minimum value (= first length Da in FIG. 3) has at least a value of 1 cm or at least a value of 2 cm.

Further, in Fig. 3, a circle K is drawn around the first boundary point Ma, the circle K having a radius R selected so that the circle K contacts the second major surface 144 of the substrate 140, but does not intersect it. In further embodiments, the substrate 140 is selected such that for all points of incidence M in the region G, the respective radii have a value that is at least 1 cm or preferably at least 2 cm (ie, R> 1 cm or R> in FIG. 3) 2cm). The region G may, as explained in FIG. 2, comprise part of the first main surface 142 or may also comprise the entire first main surface 142. Thus, the substrate 140 is selected such that it has a layer thickness that exceeds a minimum value. 4 shows a cross-sectional view through an X-ray target with the substrate 140 and the X-ray source layer 130, which is hit by the electron beam 120 and emits cone-shaped X-ray radiation 110 at a target angle β, the cone tip being the point of impact M of the electron beam 120 on the X-ray source layer 130 , The target angle β is thus the 90 ° complementary angle between the surface normal at the point of impingement M and the axis of the cone which the generated X-radiation 110 spans. Insofar as the X-radiation 110 is radiated at a right angle from the direction of the electron beam, the angle of incidence α is equal to the target angle β (β = α).

Furthermore, as shown in FIG. 4, the embodiment has an aperture 160 which blocks out part of the X-radiation 110. This makes it possible for the X-ray radiation 110 to exit the X-ray tube only in a directional area and not to spread uncontrollably in a space located around it. In addition, the diaphragm can also be used to influence by an appropriate choice of the aperture 160, the emerging intensity of the X-ray radiation 110 (the energy and intensity distribution of the Bremsstrahlung is angle-dependent).

In the embodiment shown in FIG. 4, the first main surface 142 is inclined relative to the second main surface 144 of the substrate 140 by an inclination angle Y, so that the X-ray target has a wedge-shaped structure. In the present exemplary embodiment, in which the electron beam 120 is incident perpendicular to the second main surface 144, the angle of inclination Y is also simultaneously the angle of incidence α (α = γ) with which the electron beam 120 impinges on the x-ray source layer 130. However, in other embodiments this need not be the case. The inclination angle Y may be, for example, greater than 0 ° or greater than 5 ° or in a range between 0 and 30 °. The X-ray radiation is in turn emitted into a target angle β (measured from a tangent to the X-ray source layer 130).

The shape of the X-ray target may be chosen differently in other embodiments, so that in addition to the wedge-shaped arrangement (or trapezoidal configuration) other shapes are possible -. B. that the first major surface 142 is parallel to the second major surface 144 or that the first major surface 142 is not linearly formed compared to the second major surface 144 (eg, parabolic).

FIG. 5 again shows a cross-sectional view of the X-ray target, in which the electron beam 120 in FIG. 5 is fanned onto the X-ray source layer 130 via an electric focal spot B and the electron beam 120 fanned out by a first electron beam 120 a and a second electron beam 120 b in the Cross-sectional view of Fig. 5 is limited. In the cross-sectional view shown, the fanned-out electron beam 120 is therefore delimited by a first edge point Ma and a second edge point Mb, which in turn are the starting point for the generated X-ray radiation 110. Thus, first conical spanned X-rays 110a are generated at the first edge point Ma, and second conical spanned X-rays 110b are also generated at the second edge point Mb. As shown in FIG. 5, the X-ray radiation 110a and 110b spanned by an X-ray focal spot .DELTA. During which the incident electron beam 120 forms an electric focal spot B on the X-ray source layer 130 is.

The X-ray focal spot Δ is essentially dependent on the angle of inclination Y, ie, at a smaller angle of inclination Y, the X-ray focal spot Δ also decreases for the constant electric focal spot B of the incident electron beam 120. This offers the advantage In the case of X-ray targets according to the present invention, the X-ray focal spot Δ, does not increase significantly when the electron beam 120 is fanned out and the electron beam 120 is distributed over an electrical focal spot B. It can thereby be achieved that the x-ray source layer 130 heats up less, since the electrons can impinge on the x-ray source layer 130 over a larger area and need not be focused on a narrow space.

Fig. 6 shows an embodiment of an X-ray tube with an X-ray target according to the present invention. Electrons are released from a cathode 180 and accelerated to the X-ray target having the X-ray source layer 130 with the substrate 140 and serving as an anode as the electron beam 120. The electrons may optionally be focused by lateral deflection electrodes 182a and 182b such that they strike the x-ray source layer 130 in the region G or be focused on the x-ray source layer 130 via an electric focal spot B. The x-ray radiation 110 generated in the x-ray source layer 130 leaves the x-ray source layer 130 from the side facing the electron beam 120 and leaves the x-ray tube through a stop 160. The x-ray tube further has a cooling bottom 170 and a housing 190, wherein the cooling bottom 170 is designed to fix the x-ray target along the second main surface 144 and to absorb and dissipate the heat generated in the substrate 140.

The cooling bottom 170 can be formed, for example, by a copper block or have another material that ensures efficient heat transport as well as a discharge of the electrons that have penetrated into the substrate 140. In further exemplary embodiments, the thickness of the substrate 140 may be selected such that a residual part of the kinetic energy of the electrons is emitted in the cooling bottom 170, so that the braking of the electrons can take place as follows: via the Bremsstrahlung in the X-ray genquellschicht 130, a first thermal cooling of the electrons in the substrate 140 and in a final thermal cooling of the electrons in the cooling bottom 170th

For the various angles, the following ranges can be selected by way of example. The angle of incidence α can be, for example, in a range between 0 ° and 70 ° or between 5 ° and 45 ° or between 10 ° and 30 °. The angle of inclination Y may, for example, be in a range between 0 ° and 70 ° or between 5 ° and 45 ° or between 10 ° and 30 °. The target angle β may, for example, be in a range between 0 ° and 70 ° or between 5 ° and 45 ° or between 10 ° and 30 °.

In summary, the present invention describes a layered x-ray tube target which radiates the used x-ray radiation 120 in the direction of reflection. In further embodiments, the X-ray tube target or simply X-ray target comprises two layers of different material, wherein the layer (X-ray source layer 130) facing the electron beam 120 is made of a high atomic number material, while the layer (substrate 140) facing away from the electron beam is a lower material Ordnungszahl has. By way of example, the material of the x-ray source layer 130 may have an atomic number that is greater than (or at least twice as large as) the ordinal number of the material of the substrate 140.

For example, the x-ray source layer may comprise the following materials: molybdenum (Mo), rhodium (Rh), tungsten (W), rhenium (Re), platinum (Pt), gold (Au). The substrate 140 may include, for example, the following materials: beryllium, graphite, diamond, silicon carbide, etc.

The thickness of the x-ray source layer 130 should be sufficiently small so that at most 20% of the heat deposited in the anode is deposited in the x-ray source layer 130 becomes. For example, the thickness of the x-ray source layer 130 may also be determined by the energy range of the electron beam 120 (the higher the energy range of the electron beam 120, the thicker the x-ray source layer 130 should be). On the other hand, the substrate 140 should be so thick that the surface of the substrate 140 (cooling floor) remote from the electron beam 120 can be kept at room temperature. The corresponding values for the thicknesses can be determined, for example, for an electron beam 120 with an energy between 30 keV and 100 keV or of more than 30 keV. Corresponding measurements for determining the layer thicknesses can be made, for example, in a stationary operation of the x-ray tube (in which the x-ray tube and in particular the x-ray target have reached their operating temperatures).

Claims

claims

An X-ray target for generating an X-radiation (110) in an incident region (M) of an electron beam (120) on the X-ray target, comprising:

an x-ray source layer (130) comprising a high atomic number material; and

a substrate (140) comprising a low atomic number material, wherein the high atomic number of the x-ray source layer (130) is at least twice as large as the low atomic number of the substrate (140)

wherein the x-ray source layer (130) is formed on the substrate (140) and the substrate (140) has a thickness (D) in the direction of a surface normal (150) of an interface between the x-ray source layer (130) and the substrate (140) at the impingement region ( M) of at least 1 cm,

and wherein the substrate (140) has a first main surface (142) on which the x-ray source layer (130) is formed, and a second main surface (144) on the side facing away from the x-ray source layer (130), wherein surface normals of the first and second major surfaces (142) 142, 144) intersect at an inclination angle (Y) and the inclination angle (y) has a value between 0 ° and 45 °.

2. X-ray target according to claim 1, wherein the layer thickness (D) of the substrate (140) at least 1.5 cm or at least 2 cm.

3. X-ray target according to one of the preceding claims, wherein the impact region (M) within a region (G) on the X-ray source layer (130) and the region (G) by scaling one through the X-ray source layer (130) formed surface, which faces away from the substrate (140) is formed by a predetermined factor,

and wherein the substrate (120) is formed to have a layer thickness (D) of at least 1 cm for each impinging region (M) in the region (G).

4. X-ray target according to one of the preceding claims, wherein the angle of inclination (Y) is set such that the electron beam (120) forms an electric focal spot (B) on the x-ray source layer (130) with normal incidence with respect to the second main surface (144) and the X-radiation (110) forms an X-ray focal spot (Δ) on the X-ray source layer (130),

wherein the X-ray focal spot (Δ) is in a range between 1 micron and 500 microns.

5. X-ray target according to one of the preceding claims, wherein the material of the x-ray source layer (130) molybdenum or gold or platinum or tungsten and / or the substrate (140) beryllium or graphite o- has the diamond or silicon carbide.

6. X-ray target according to one of the preceding claims, wherein the substrate (140) has a first main surface

(142) and a second major surface (144), wherein on the first major surface (142) the x-ray source layer (130) is formed, and wherein the second major surface (144) is connectable to a cooling bottom (170).

The X-ray target according to claim 6, wherein the surface normals of the first main surface (142) and the second main surface (144) intersect at an inclination angle (γ) and the inclination angle (Y) is greater than zero or greater than 5 ° or in a range between 0 ° and 30 °.

8. X-ray target according to one of the preceding claims, in which the x-ray source layer (130) has a further

Has layer thickness and the further layer thickness is below a maximum value, wherein the maximum value is determined such that upon irradiation of the X-ray target with an electron beam in an energy range of more 30 keV 20% of the amount of heat generated in the X-ray target in the X-ray source layer (130) is deposited ,

9. X-ray target according to claim 8, wherein the energy range is between 30 keV and 100 keV.

10. X-ray target according to one of the preceding claims, wherein the layer thickness (D) of the substrate (140) has a minimum layer thickness and the Mindestschichtdi- bridge is selected such that upon irradiation of the X-ray target with an electron beam (110) with an energy between 30 keV and 100 keV, the surface of the substrate (140) facing away from the electron beam is heated to a temperature of 40 ^° C.

11. Use of an X-ray target according to one of claims 1 to 10 in reflection mode in an X-ray tube.

12. X-ray tube for generating an X-ray beam (110) by an electron beam (120) in an impact region (M) of the electron beam (120), comprising:

an anode comprising a substrate (140) and an x-ray source layer (130) formed on the substrate (140), the substrate (140) having a thickness (D) in the direction of a surface normal (150) of an interface between the x-ray source layer (130) and the substrate (140) at the impact region (M) of at least 1 cm;

a cathode (180) configured to release electrons of the electron beam (120);

a cooling floor (170) on which the substrate (140) of the X-ray target is arranged; and

a housing (190) having an exit window (160),

wherein the exit window (160) is disposed in the housing (190) so as to be passable to the x-ray radiation (110), and wherein the anode is configured to emit x-ray radiation (110) from the x-ray source layer (130).

13. X-ray tube according to claim 12, in which the substrate (140) and the cooling bottom (170) are impermeable to X-ray radiation.

14. A method for producing an X-ray target for generating an X-radiation (110) in an impact region (M) of an electron beam (120) on the X-ray target, comprising the following steps:

Providing a substrate (140) comprising a low atomic number material; and

Forming an x-ray source layer (130) on the substrate (140), wherein the x-ray source layer (130) comprises a high atomic number material, wherein the high atomic number of the x-ray source layer (130) is at least twice the low atomic number of the substrate (140)

and wherein the substrate (140) has a layer thickness (D) in the direction of a surface normal (150) at the impact surface. region (M) of at least 1 cm, and the substrate (140) has a first major surface (142) on which the x-ray source layer (130) is formed and a second major surface (144) on the x-ray source layer (130) Side, wherein surface normals of the first and second main surfaces (142, 144) intersect at an inclination angle (Y) and the inclination angle (γ> has a value between 0 ° and 45 °.