DIAPHRAGM FOR AN X-RAY TUBE AND X-RAY TUBE WITH SUCH A DIAPHRAGM

Abstract

A diaphragm for restricting a cross section of an electron beam of an X-ray tube includes a base body made of a first material, which has a first cylindrical or conical diaphragm aperture, and an additional body made of a second material, which has a second cylindrical or conical diaphragm aperture. The additional body in the installed state is arranged on the side near the electron source, wherein the atomic number of the first material is greater than the atomic number of the second material. The diameters of the diaphragm apertures at the end far from the electron source are not smaller than at the end near the electron source, and the second diaphragm aperture at its end far from the electron source lies completely inside the first diaphragm aperture at its end near the electron source.

Claims

1. A diaphragm for restricting a cross section of an electron beam of an X-ray tube with a base body made of a first material, which has a first cylindrical or conical diaphragm aperture, and with an additional body made of a second material, which has a second cylindrical or conical diaphragm aperture, wherein the additional body in the installed state is arranged on the side near the electron source, wherein the atomic number of the first material is greater than the atomic number of the second material, wherein the diameters of the diaphragm apertures at the end far from the electron source are not smaller than at the end near the electron source, wherein the second diaphragm aperture at its end far from the electron source lies completely inside the first diaphragm aperture at its end near the electron source.

2. A diaphragm according to claim 1, wherein the first diaphragm aperture and the second diaphragm aperture are arranged concentrically relative to each other.

3. A diaphragm according to claim 1, wherein the first diaphragm aperture and the second diaphragm aperture are in each case conical and the diameter of the first diaphragm aperture at its end near the electron source, the first diaphragm entrance aperture, is greater than the diameter of the second diaphragm aperture at its end far from the electron source, the second diaphragm exit aperture.

4. A diaphragm according to claim 1, wherein the additional body, on its surface far from the electron source, and the base body, on its surface near the electron source, are in contact with each other, in particular over their entire surface.

5. A diaphragm according to claim 1, wherein the first material is a metal, in particular molybdenum, tungsten or titanium, and the second material is aluminium, beryllium, silicon, carbon, in particular in the form of graphite, boron or a chemical compound of one or more of these elements.

6. A diaphragm according to claim 1, wherein the difference between the atomic numbers of first material and second material is at least sixteen, preferably at least thirty six.

7. A diaphragm according to claim 1, wherein the base body, on its surface near the electron source, has a recess with a first bearing surface, which corresponds to the outer contour of the surface far from the electron source, the second bearing surface, of the additional body and is slightly larger than this.

8. A diaphragm according to claim 1, wherein the additional body, on its surface near the electron source, has the shape of a concave spherical surface segment.

9. An X-ray tube, in particular microfocus X-ray tube, with means for directing an electron beam onto a target and a diaphragm according to claim 1 arranged in the propagation path of the electron beam.

10. An X-ray tube according to claim 9, wherein there is a diaphragm holder which surrounds both the additional body and the base body of the diaphragm at their radial ends such that additional body and base body are pressed against each other.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Further advantages and details of the invention are explained in more detail in the following with reference to the embodiment example represented in the figures. There are shown in:

[0018] FIG. 1 a perspective view of a base body according to the invention,

[0019] FIG. 2 a longitudinal section through the base body of FIG. 1,

[0020] FIG. 3 a perspective view of an additional body according to the invention,

[0021] FIG. 4 a longitudinal section through the additional body of FIG. 3,

[0022] FIG. 5 a longitudinal section through a diaphragm with base body and additional body according to FIG. 6,

[0023] FIG. 6 a perspective view of a diaphragm according to the invention with the base body of FIGS. 1 and 2 and the additional body of FIGS. 3 and 4 and

[0024] FIG. 7 a schematic sectional drawing of a diaphragm according to the invention in a part of an X-ray tube.

DETAILED DESCRIPTION OF THE INVENTION

[0025] A base body 1 according to the invention of a diaphragm for an X-ray tube is represented in FIGS. 1 and 2, wherein the perspective view of FIG. 1 shows the base body 1 from a direction at an angle from below in relation to the cross section of FIG. 2.

[0026] The base body 1 is formed axisymmetric about its longitudinal centre axis 7. It is part of a diaphragm for restricting an electron beam 5 (see FIG. 7) which, in the X-ray tube, serves to generate X-radiation at a target 9 (see FIG. 7).

[0027] The base body 1 is made of a first material, which must be heat-resistant to a high degree due to its position in the X-ray tube and must have a high thermal conductivity in order to remove the heat being generated in it. Moreover, as far as possible, it must not exert a magnetic influence, in order not to interfere with the electric fields in the X-ray tube. It is preferably made of a metal, as are the diaphragms known in the state of the art, in particular of molybdenum, tungsten or titanium.

[0028] Along its longitudinal centre axis 7, there is a first diaphragm aperture 10 which widens conically from a first diaphragm entrance aperture 11, which is located on the side near the electron source in the installed state, to a first diaphragm exit aperture 12, which is located on the side far from the electron source in the installed state.

[0029] On the side near the electron source the base body 1 has a circumferential flange 14 with a recess formed concentrically about the longitudinal centre axis, which recess forms a flat first locating surface 15.

[0030] On its side far from the electron source the base body 1 has a short hollow cylindrical extension which is at a large radial distance from the first diaphragm exit aperture 12.

[0031] An additional body 2 according to the invention of the diaphragm is represented in FIGS. 3 and 4, wherein the perspective view of FIG. 3 shows the additional body 2 from a direction at an angle from above in relation to the cross section of FIG. 4, It is represented enlarged in relation to the base body 1 of FIGS. 1 and 2.

[0032] The additional body 2 is formed axisymmetric about its longitudinal centre axis 7. It is part of the diaphragm for restricting the electron beam 5 (see FIG. 7).

[0033] The additional body 2 is also made of a second material, which must be heat-resistant to a high degree due to its position in the X-ray tube and must have a high thermal conductivity in order to remove the heat being generated in it. Moreover, as far as possible, it must not exert a magnetic influence, in order not to interfere with the electric fields in the X-ray tube. It is preferably made of graphite, a carbon compound, beryllium or aluminium.

[0034] Along its longitudinal centre axis 7, there is a second diaphragm aperture 20 which widens conically from a second diaphragm entrance aperture 21, which is located on the side near the electron source in the installed state, to a second diaphragm exit aperture 22, which is located on the side far from the electron source in the installed state.

[0035] The radial outer surface is formed cylindrical in its lower part and as a conical jacket 25 in the upper part.

[0036] On the side near the electron source the additional body 2 has the shape of a concave spherical surface segment. On the side far from the electron source, in contrast, it has a fiat second bearing surface 24.

[0037] A cross sectioncomparable to the cross sections of FIGS. 2 and 4through the entire diaphragm is represented in FIG. 5. The two individual parts base body 1 and additional body 2 are represented in the correct size ratio relative to each other; compared with FIGS. 1 to 4, however, the scale is changed.

[0038] Base body 1 and additional body 2 are joined to each other such that their flat locating surfaces 15, 24 abut against each other and the lower end of the additional body 2 lies in the recess 13 of the base body 1. A radial invariability of the two parts with respect to each other is thus ensured. The alignment of the two parts is such that their respective longitudinal centre axes 7 coincide and form a common longitudinal centre axis 7, about which the entire obtained structure is axisymmetric.

[0039] The aperture angle of the cone of the second diaphragm aperture 20 is much smaller than the aperture angle of the cone of the first diaphragm aperture 10. In the represented embodiment example, the limiting case is represented, where second diaphragm exit aperture 22 and first diaphragm entrance aperture 11 have the same diameter. Within the framework of the invention, it is also possible for the diameter of the second diaphragm exit aperture 22 to be smaller than the diameter of the first diaphragm entrance aperture 11 (see FIG. 7).

[0040] FIG. 6 shows the diaphragm with base body 1 and additional body 2 in a perspective representation, as corresponds to FIG. 4 in terms of the direction; FIG. 5 is the longitudinal section of FIG. 6. In order to achieve not only a radial positional change of the two parts of the diaphragmbase body 1 and additional body 2but also an axial positional change along the longitudinal centre axis 7, there is a diaphragm holder (not represented). The diaphragm holder presses, from above in FIG. 6, on a part of the conical jacket 25 of the additional body 2 and butts against a diaphragm holder bearing surface 8 facing the electron source (see also FIGS. 2 and 5) of the flange 14 of the base body 1. It thus prevents an axial movement of the two parts base body 1 and additional body 2 relative to each other.

[0041] FIG. 7 shows a schematic representation of a part of an X-ray tube in the region of the target 9 in section. The target 9 is a target 9 known from the state of the art with a support material 3 and, applied thereto, target material 4 which the electron beam 5, which comes from an electron source (not shown), strikes and there produces X-radiation 6, The represented. X-ray tube is a transmission tube. without this limiting the invention.

[0042] The diaphragm serves to restrict the size of the focus of the X-ray tube, which means that the focus is only as large as electrons come through the first and second diaphragm apertures 10, 20.

[0043] In order to prevent the electrons of the electron beam 5 which strike the diaphragm from generating interfering X-radiation 6, the additional body 2 must be made of a material such that as little as possible and preferably much softer X-radiation than that which is produced at the target material 4 forms. For this purposein contrast to the state of the art, where the diaphragm material is a metal (in the case of the invention this only applies to the base body 1 of the diaphragm)the additional body 2 is manufactured from graphite. As graphite has a low atomic number, the proportion of short-wave X-radiation is reduced, with the result that only a very small portion of stray radiation penetrates the target 9 and can cause image errors.

[0044] In order that electrons of the electron beam 5, which do not fly parallel to the longitudinal centre axis 7. do not also strike the metallic material of the base body 1in the embodiment example it consists of molybdenum (with a high atomic number) and produce stray radiation, the first diaphragm aperture 10 has a cone shape widening towards the target 9. The base body 1 also has the function of shielding against the stray radiation being formed in the interior of the X-ray tube. For this a high atomic number and density is advantageous.

[0045] The aperture angle of the cone of the second diaphragm aperture 20 is chosen to be small in order to prevent astigmatic effects.

[0046] While the foregoing is directed to embodiments of the present invention, other and further embodiments and advantages of the invention can be envisioned by those of ordinary skill in the art based on this description without departing from the basic scope of the invention, which is to be determined by the claims that follow.

LIST OF REFERENCE NUMBERS

[0047] 1 base body [0048] 2 additional body [0049] 3 support material [0050] 4 target material [0051] 5 electron beam [0052] 6 X-radiation [0053] 7 longitudinal centre axis [0054] 8 diaphragm holder bearing surface [0055] 9 target [0056] 10 first diaphragm aperture [0057] 11 first diaphragm entrance aperture [0058] 12 first diaphragm exit aperture [0059] 13 recess [0060] 14 flange [0061] 15 first bearing surface [0062] 20 second diaphragm aperture [0063] 21 second diaphragm entrance aperture [0064] 22 second diaphragm exit aperture [0065] 23 surface near the electron source [0066] 24 second bearing surface [0067] 25 conical jacket