Component or electron capture sleeve for an X-ray tube and X-ray tube having such a device

Abstract

A component part in a vacuum area of an X-ray tube with an opening through which an electron beam is guided. The component part includes a base body made of a first material, wherein the first material is a metal. Arranged on a surface forming the opening is a second material having an atomic number which is smaller than an atomic number of the first material. A target support is attached to an end of the component part. The target support supports a target which is aligned with a lens diaphragm formed at the end of the component part. The target support has a base body made of a first material which is a metal, and a second material formed on a surface of the base body that is selectively exposed to the electron beam and which extends between the target and the lens diaphragm.

Claims

1. A component part in a vacuum area of an X-ray tube with an opening through which an electron beam is guided, the component part including a beam tube, the component part comprising: a base body made of a first material, wherein the first material is a metal and the beam tube is made from the first material, at least one of a core of a coil which forms at least a portion of the opening; and wherein arranged on a surface forming the opening which includes the beam tube, said surface being selectively exposed to the electron beam, is a second material having an atomic number which is smaller than an atomic number of the first material.

2. The component part according to claim 1, wherein the first material is one of molybdenum, iron, tungsten or titanium; and the second material is aluminum, beryllium, silicon, carbon, boron or a chemical compound of one or more of these elements of the second material.

3. The component part according to claim 1, wherein the atomic numbers of the first material and the second material differ by at least 16.

4. The component part according to claim 1, wherein the second material is formed as a separate additional body in a form of at least one tubular additional body.

5. The component part according to claim 4, wherein the at least one tubular additional body rests against an entire surface of the base body.

6. The component part according to claim 4, wherein the at least one tubular additional body covers several component parts exposed to the electron beam.

7. A microfocus X-ray tube configured to direct the electron beam onto a target, and the component part according to claim 1 arranged in a propagation path of the electron beam.

8. The microfocus X-ray tube according to claim 7, wherein the X-ray tube is constructed such that the electron beam cannot strike the first material, but only the second material at any point along the propagation path of the electron beam from a cathode to the target.

9. The component part according to claim 1, wherein the second material is graphite.

10. The component part according to claim 1, wherein the atomic numbers of the first material and the second material differ by at least 36.

11. The component part according to claim 1, wherein the second material is applied in a form of a coating or a foil on a surface of the first material.

12. A microfocus X-ray tube including the component part of claim 1, the microfocus X-ray tube configured to direct the electron beam onto a target which is attached to an end of the component part, the target being made from the first material with the second material provided thereon, wherein the target and the component part are arranged in a propagation path of the electron beam.

13. An apparatus comprising: a component part suitable for implementation in a vacuum area of an X-ray tube with an opening through which an electron beam is guided, the component part including: a beam tube for directing the electron beam to a target; a base body made of a first material, wherein the first material is a metal; wherein arranged on an interior surface forming the opening, is a second material having an atomic number which is smaller than an atomic number of the first material; and the apparatus further comprising: a target support attached to an end of the component part, the target support supporting the target which is aligned with a lens diaphragm formed at an end of the beam tube, the target support having a second base body made of the first material, and the second material being formed on a surface of the second base body that is selectively exposed to the electron beam and which extends between the target and the lens diaphragm.

14. A microfocus X-ray tube including the apparatus of claim 13, the microfocus X-ray tube configured to direct the electron beam onto the target which is attached to the end of the component part by the target support, the target and the target support being made from the first material with the second material provided thereon, wherein the target, the target support and the component part are arranged in a propagation path of the electron beam.

15. The apparatus according to claim 13, wherein the first material is one of molybdenum, iron, tungsten or titanium; and the second material is aluminum, beryllium, silicon, carbon, boron or a chemical compound of one or more of these elements of the second material.

16. The apparatus according to claim 13, wherein the second material is graphite.

17. The apparatus according to claim 13, wherein the atomic numbers of the first material and the second material differ by at least 16.

18. The apparatus according to claim 13, wherein the atomic numbers of the first material and the second material differ by at least 36.

19. The apparatus according to claim 13, wherein the second material is applied in a form of a coating or a foil on a surface of the first material.

20. The apparatus according to claim 13, wherein the second material is formed as a separate additional body in a form of at least one tubular additional body.

21. The apparatus according to claim 20, wherein the separate additional body rests against an entire surface of the base body.

22. The apparatus according to claim 20, wherein the at least one tubular additional body covers several component parts exposed to the electron beam.

23. A microfocus X-ray tube including the apparatus of claim 13, the microfocus X-ray tube configured to direct the electron beam onto the target, and wherein the component part is arranged in a propagation path of the electron beam.

24. The microfocus X-ray tube according to claim 23, wherein the X-ray tube is constructed such that the electron beam cannot strike the first material, but only the second material at any point along the propagation path of the electron beam from a cathode to the target.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The single FIG. shows: a drawing of a longitudinal section through a part of an X-ray tube with an additional body according to the invention.

DETAILED DESCRIPTION

(2) A detail of a microfocus X-ray tube according to the invention in the area of its condenser 1 and its objective 2 up to a target 5 is represented in a schematic longitudinal section in the FIG. The rest of the microfocus X-ray tube, not represented, corresponds to the state of the art and is not relevant to the invention. Instead of a microfocus X-ray tube, it can also be another type of X-ray tube.

(3) Condenser 1 and objective 2 are arranged around a beam tube 3 for an electron beam 13shown as a dashed line. The condenser 1 lies in front of the objective 2 in the direction of the electron beam 13.

(4) The condenser 1 contains a condenser coil only the condenser core 8 of which is represented. The objective 2 is connected to the condenser coil in the propagation direction of the electron beam 13. The objective 2 contains an objective coil only the objective core 9 of which is represented.

(5) The beam tube 3 extends in the propagation direction of the electron beam 13 beyond the end of the condenser 1 into the area of the objective 2.

(6) A lens diaphragm 4 is connected to the objective 2 in the propagation direction of the electron beam 13.

(7) In order to prevent electrons of the electron beam 13 from striking the beam tube 3, which is made of a metal, or the surfaces, facing the electron beam 13, of the condenser core 8 as well as the objective core 9, which both consist of iron, and thereby generating stray radiation because of the high atomic number of the materials used, there is arranged between these surfaces and the electron beam 13 an additional body 10 which consists of graphite. Because graphite with a low atomic number is used in the additional body 10, if the latter is struck by electrons of the electron beam 13 only long-wave X-radiation forms. Thus the proportion of short-wave X-radiation is reduced, with the result that no stray radiation, or only a very small portion of it, can form.

(8) The additional body 10 extends in longitudinal direction over the whole length of the beam tube 3 and of the objective 2 up to the lens diaphragm 4. It is formed in one piece and rests with its outer surface against the opening 14 of the beam tube 3 and against the opening 15 of the objective core 9. Its inner surface is formed cylindrical. Because of the step between the end of the beam tube 3 and the objective core 9, its outer surface is formed as a cylinder with a step and has a tubular shape.

(9) The lens diaphragm 4 has a lens diaphragm-base body 7 and arranged in front of it a lens diaphragm-additional body 11 in the propagation direction of the electron beam 13. The lens diaphragm 4 serves with its opening 16 to restrict the electron beam 13, and thus the focus which serves to generate X-radiation on a target 5 in the X-ray tube.

(10) The lens diaphragm-base body 7 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 generated in it. Moreover, it must as far as possible exert no 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.

(11) The lens diaphragm-additional body 11 is made of a second material which must alsolike the first materialbe 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 generated in it. Moreover, it must as far as possible exert no magnetic influence in order not to interfere with the electric fields in the X-ray tube. In order to prevent the electrons of the electron beam 13, which strike the lens diaphragm 4, from generating interfering X-radiation, the lens diaphragm-additional body 11 must be made of a material which generates as little as possible and preferably considerably softer X-radiation than that which is generated in the target 5. It is therefore manufactured from a carbon compound, beryllium or aluminiumparticularly preferably 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 5 and can cause image errors.

(12) The opening 16 of the lens diaphragm 4 widens conically in the propagation direction of the electron beam 13, so that any electrons of the electron beam 13 scattered on the lens diaphragm-additional body 11 cannot strike the metal of the lens diaphragm-base body 7, which would result in the generation of stray radiation.

(13) Such a lens diaphragm is described in DE 10 2016 013 747.

(14) As an alternative to the represented lens diaphragm 4 with a division in the propagation direction of the electron beam 13 into lens diaphragm-base body 7 and lens diaphragm-additional body 11 shielding same, a lens diaphragm 4 according to the invention could be designed such that the shield of the lens diaphragm-additional body 11 is arranged in radial directionrelative to the electron beam 13around the lens diaphragm-base body 7, wherein the lens diaphragm-base body 7 does not project radially over the end of the tubular additional body 10 to which it is connected. It is also then achieved that no electrons of the electron beam 13 can strike the metal of the lens diaphragm-base body 7, which would generate stray radiation.

(15) The target 5a transmission target in the embodiment example representedwhich is secured to a target support 6 connected to the objective 2, is connected to the lens diaphragm 4 in the propagation direction of the electron beam 13.

(16) The target support 6 forms the vacuum seal between objective core 9 and target 5 in the front area of the microfocus X-ray tube. It serves to mechanically stabilize the target 5, as the latter is only approximately 300 m thick in some areas. It is helpful for the best possible removal of the heat that forms on the target 5 if the target support 6 consists of a metal such as for example brass. As a portion of the electrons are backscattered when the electron beam 13 strikes the target 5, these could strike the target support 6. Then stray radiation would form in the target support 6.

(17) In order to prevent this, the whole surface of the target support 6 between objective 2 and target 5 is covered with a body made of graphite which is denoted electron capture sleeve 12. The electron capture sleeve 12 is formed like the additional body 10 in one piece and rests against the whole surface of the target support 6 facing the electron beam 13. The electron capture sleeve 12 is at earth potential in order to be able to directly remove backscattered electrons. Because of the proximity to the target 5 and to the focal spot, the material of the electron capture sleeve 12 must tolerate high temperatures and must not interfere with the trajectory of the electrons. A metal such as for example molybdenum is often used for the electron capture sleeve 12. If a metal is used, the electron capture sleeve 12 would itself in turn generate stray radiation. Therefore a material with a low atomic number and density is to be preferred.

(18) Because of the additional parts according to the invention, additional body 10 and electron capture sleeve 12 in conjunction with the lens diaphragm-additional body 11, electrons of the electron beam 13 are prevented from generating stray radiation at any point, with the result that no image errors are caused by stray radiation.

LIST OF REFERENCE NUMBERS

(19) 1 condenser 2 objective 3 beam tube 4 lens diaphragm 5 target 6 target support 7 lens diaphragm-base body 8 condenser core 9 objective core 10 additional body 11 lens diaphragm-additional body 12 electron capture sleeve 13 electron beam 14 opening of the beam tube 15 opening of the objective core 16 opening of the lens diaphragm