Abstract
An anode head for an anode of an X-ray generating device is provided. The anode head is made of an X-ray attenuating material and has a first opening with a first diameter for a primary electron beam, wherein a circular aperture of a secondary electron absorbing material and having a second opening which is arranged concentrically to the first aperture and has a second diameter which is smaller than the first diameter.
Claims
1. An anode head for an anode with: a target of an X-ray generating device, said anode head being made of an electrically conductive material and having a first opening with a first diameter (D1) for a primary electron beam (PES) directed to said target, and a circular aperture with a second opening concentric with said first opening and having a second diameter (D2) smaller than said first diameter (D1), the circular aperture made of an oxide ceramic to avoid influencing a primary electron beam passing through the circular aperture and to facilitate capturing secondary electrons generated by the anode.
2. The anode head according to claim 1, wherein the anode head is made of copper or an electrically conductive element having a high atomic number.
3. The anode head according to claim 2, wherein the anode head consists of tungsten, tantalum, or an alloy of copper with tungsten or tantalum.
4. The anode head according to claim 1, wherein the circular aperture is made completely or at least in one disc section in the form of a pinhole disc and is inserted into the anode head in an associated recess, wherein the recess is located on the side of the anode head facing the anode in an installation position or on the side of the anode head facing away from the anode in the installation position.
5. The anode head according to claim 1, wherein the circular aperture is made completely or in a cylinder section in the form of a hollow cylinder with an outside diameter equal to the first diameter (D1) and is arranged in the first opening of the anode head.
6. The anode head according to claim 1, wherein the circular aperture is made completely or in a cap portion in the form of a cap which is attached to the side of the anode head remote from the anode in an installation position.
7. The anode head according to claim 1, wherein the electrical conductivity of the circular aperture is adjusted by coating with an electrically conductive material and/or by doping the oxide ceramic in such a way that the circular aperture is not electrically charged during operation by trapped secondary electrons.
8. The anode head according to claim 1, wherein the material thickness of the circular aperture in the direction of the primary electron beam (PES) and/or the second diameter (D2) are designed such that a predetermined proportion of the secondary electrons produced on the target or the anode head during operation are captured by the circular aperture.
9. The anode head according to claim 1, wherein the circular aperture is electrically conductively connected to the anode head.
10. The anode head according to claim 1, wherein the second diameter (D2) of the second opening is adjusted such that the size of the focal spot of the primary electron beam (PES) on the target is unchanged compared to an anode head without the circular aperture.
11. The anode head according to claim 1, wherein the anode is a fixed anode or a rotating anode.
12. An X-ray generating device with an arrangement comprising a cathode and an anode, which has an anode head according to claim 1.
13. An X-ray inspection apparatus with an X-ray generating device according to claim 12.
14. A converting method for an X-ray inspection apparatus comprising a first X-ray generating device with an arrangement of a cathode and an anode having an anode head without a circular aperture for shielding secondary electrons, the method comprising the steps of dismounting said first X-ray generating device; and installing an X-ray generating device according to claim 12.
15. The anode head according to claim 1, wherein the anode head defines a chamber having a chamber diameter, wherein the chamber diameter is larger than both the first diameter and the second diameter, wherein the chamber is positioned between the anode and the first opening, wherein the chamber is positioned between the anode and the second opening, and wherein the chamber is concentric with both the first opening and the second opening.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) FIG. 1 shows a conventional X-ray generating device with a known anode head.
(2) FIG. 2 shows trajectories of simulated secondary electrons at the anode head without the aperture of the disclosure in FIG. 1.
(3) FIG. 3 shows an X-ray generating device with an example of an anode head of the disclosure.
(4) FIG. 4 shows trajectories of simulated secondary electrons on the anode head of the disclosure in FIG. 3.
(5) FIGS. 5A-5C non-exhaustively show different design examples for the anode head according to the disclosure.
(6) FIG. 6 shows a schematic cross-section of a side view of an exemplary X-ray inspection apparatus with an X-ray generating device, as shown in FIG. 3, for example.
(7) FIG. 7 shows a block diagram of a converting process according to the disclosure.
DETAILED DESCRIPTION
(8) Compared to FIG. 1, FIG. 3 shows a design example of an anode head 113, improved according to the disclosure, for an anode 108 of an X-ray generating device 100. The anode head 113 initially includes an electrically conductive material, for example copper, and has a first opening 114 with a first diameter D1 for a primary electron beam PES.
(9) In addition to the anode head 13 in FIG. 1, the anode head 113 is equipped with a circular aperture 116, which has a second opening 117 concentric with the first opening 114 in the anode head 113 and a second diameter D2. The second diameter D2 is smaller than the first diameter D1. The circular aperture 116 reduces the cross section of the first opening 114 and thus prevents a large proportion of the secondary electrons produced on the anode body 111 and/or target 112 during operation from leaving the anode head 113 through the first opening 114. This leads to a corresponding reduction of the undirected X-ray radiation occurring at the anode head 13 of FIG. 1.
(10) As in FIG. 1, the first opening 114, in intended combination with the anode body 111, is located above the focal spot located on the target 112 encased by the anode body 111, so that the primary electron beam PES, which is generated in a known manner by the heated cathode 107 and the high voltage applied between the cathode 107 and the anode 108, can pass through the first opening 114 and hit the target 112 to generate the desired X-ray radiation RS.
(11) As in FIG. 1, the anode head 113 contains an exit opening 115 for the generated X-ray radiation RS. The anode head 113 fulfils a collimator function with the exit opening 115 by only leaving the anode head 113 unaffected by X-rays directed to the exit area 106 in the housing 102 of the X-ray generating device 100.
(12) For an optimum shielding effect, the anode head 113 is made of an element with a high atomic number, such as a heavy metal or heavy metal alloy, for example tungsten, tantalum, or an alloy of one or both of these materials.
(13) In order not to influence the primary electron beam PES, the circular aperture 116 is made of a material with a high resistivity. In the design example, circular aperture 116 is made of an oxide ceramic, namely an alumina ceramic.
(14) In FIG. 3, the circular aperture 116 is monolithically designed in the form of a circular aperture disc (pinhole disc) and inserted in a corresponding recess in the anode head 113, which is located in the installation position on the side of the anode head 113 facing the anode 108. In other words, the circular aperture 113 is located on the inside of the first opening 114 of the anode head 113. The circular aperture 116 need not be monolithic, but can also be composed of several sections.
(15) The surface conductivity of the circular aperture 116 in the design example is adjusted by doping the base material, i.e. the aluminum oxide ceramic, of the circular aperture 116 in such a way that the circular aperture 116 cannot become electrically charged during operation by trapped secondary electrons. This prevents the formation of charge nests on the circular aperture 116 and a corresponding undesirable effect on the primary electron beam PES.
(16) Alternatively or additionally, the desired surface conductivity of the circular aperture 116 can also be adjusted by coating it with an electrically conductive material.
(17) The material thickness MD of the circular aperture 116, which is measured in the direction of the primary electron beam PES, and the second diameter D2 of the second opening 117 are designed in such a way that, compared to the anode head 13 without circular aperture 116 (FIG. 1), a predetermined proportion of the secondary electrons produced during operation on the anode body 111 and/or target 112 are trapped by the circular aperture 116 or prevented from leaving the anode head 113.
(18) The second diameter D2 of the second opening 116 of the circular aperture 116 is further adjusted so that the size of the focal spot of the primary electron beam PES on the target 112 is unchanged compared to the anode head 13 without circular aperture 116 (FIG. 1).
(19) The circular aperture 116 is permanently connected to the anode head 113 by soldering. An active soldering process was used as the soldering method. Alternatively or additionally, the circular aperture 116 can also be attached mechanically and electrically conductively by wedging it to the anode head 113.
(20) In the embodiment in FIG. 3, anode 108 is a fixed anode (standing anode). Basically, the principles of the disclosure proposed here can be easily transferred to an arrangement with a rotating anode.
(21) FIG. 4 shows the trajectories of simulated secondary electrons at the anode head 113 of the X-ray generating device 100 shown in FIG. 3, which is in accordance with the disclosure. In FIG. 4 it can be clearly seen that of the secondary electrons present in the chamber K formed by the anode head 113, circular aperture 116 and anode body 111, only a few can leave the anode head 113 through the first opening 114 of the anode head 113 in comparison with the situation in FIG. 2, since they are intercepted and captured by the circular aperture 116 with the smaller second opening 117. Since the circular aperture 116 has a predetermined surface conductivity, the captured secondary electrons can flow off via the electrically conductive anode head 113 to the anode 108.
(22) FIGS. 5A-5C non-exhaustively show further possible embodiments for an anode head according to the disclosure.
(23) In FIG. 5A, in comparison to the implementation in FIG. 3, the circular aperture 116 is designed in the form of a hollow cylinder with an outer diameter corresponding to the first diameter D1 of the first opening 114 and is inserted into the first opening 114 of the anode head 113 with a precise fit and connected to the anode head 113 mechanically (e.g. by wedging) and/or by active soldering. The effective material thickness MD of the circular aperture 116 for intercepting secondary electrons thus corresponds to the material thickness of the end face of the anode head 113.
(24) In FIG. 5B, circular aperture 116 is a combination of the implementations in FIGS. 3 and 5A, i.e. circular aperture 116 has a disc section S, which has the shape of a circular aperture disc (cf. FIG. 3), and a cylinder section Z, which has the shape of a hollow cylinder (cf. FIG. 5A). In the overall cross-section, the circular aperture 116 thus has the shape of a large letter “T”, the “T” in FIG. 5B being upside down. In FIG. 5B the circular aperture 116 is inserted from the inside into the corresponding recess on the anode head 113. The cylinder section Z is fitted into the already existing first opening 114 of the anode head 113 and the disc section S is inserted into the already existing recess for the anode body 111 from the inside of the anode head 113 and connected to the anode head 113 mechanically (e.g. by wedging) and/or by active soldering. The effective material thickness MD of the circular aperture 116 for intercepting secondary electrons thus corresponds to the material thickness of the front surface of the anode head 113 and additionally to the material thickness of the disc section S of the circular aperture 116.
(25) In FIG. 5C the circular aperture 116 is designed in the form of a cap which is attached to the side of the anode head 113 facing away from the anode 108 in the installation position, i.e. outside the front face of the anode head 113, and is connected to the anode head 113 mechanically (e.g. by wedging) and/or by active soldering. The effective material thickness MD of the circular aperture 116 for intercepting secondary electrons corresponds to the material thickness of the front side of the circular aperture 116.
(26) FIG. 6 shows a schematic cross-section of a side view of an exemplary X-ray inspection apparatus 200 with an X-ray generating device 100, as shown for example in FIG. 3. X-ray inspection apparatus 200 has two radiation protection curtains 201, 203, which are each located at an entrance and an exit of a radiation tunnel 202 of the X-ray inspection apparatus 200. Between the two radiation protection curtains 201, 203 there is a radiation area 205 inside the radiation tunnel 202. In the radiation area 205 at least one X-ray generating device 100 and at least one detector array 207 aligned with it are arranged. A conveyor system 209 is used to transport an inspection object, for example a piece of baggage 211, into and through the radiation tunnel 202. The mode of operation of the X-ray inspection apparatus 200 is known per se and need not be explained here.
(27) FIG. 7 shows a block diagram of a converting procedure for an X-ray inspection apparatus which has a first X-ray generating device 1, as shown in FIG. 1, for example, and which has an anode head 13 without the circular aperture 116, as required by the invention, for shielding secondary electrons. The conversion method includes at least the following steps. A first step S1 of dismounting the first X-ray generating device 1. A second step S2 of mounting an X-ray generating device 100 as shown for example in FIG. 3. Thus, existing X-ray inspection apparatus can obtain the advantages of the disclosure described here by a simple exchange.
