DE102009033607A1 - X-ray tube and anode for an X-ray tube - Google Patents

Abstract

The anode (3) has a barrier layer (9) arranged between a carrier (8) and an emitter layer (10) and made from material e.g. rhenium, osmium or hafnium, where the anode is arranged above an X-ray radiation emitting window. The carrier is made from material e.g. beryllium or aluminum, having smaller atomic number or made from carbon fiber-reinforced graphite. The carrier has thickness of 90 micrometers to 3 mm, and the emitter layer has thickness of 10 micrometers. The emitter layer is made from material e.g. tungsten, copper, molybdenum or tantalum, having large atomic number. An independent claim is also included for an X-ray device comprising an anode.

Description

The The invention relates to an X-ray tube and a Anode for an X-ray tube as well X-ray machine with such an X-ray tube.

X-ray tubes are used to generate X-radiation. X-rays is used, among others, in medical imaging used, in the examination of materials, or in fluoroscopy as part of safety investigations.

X-rays is typically generated in the form of bremsstrahlung, which at the absorption of high-energy electrons in an anode arises. For this purpose, electrons are generated by a cathode in a vacuum and accelerated by means of high voltage in the direction of an anode. Of the Electron beam is focused on the anode. In the anode will be the electrons are decelerated by the anode material, which is why typically one High atomic number material is used as the anode material. Materials or elements with high atomic number cause sufficient strong deceleration of the electrons. When braking arises as the Brake radiation generated X-rays, which for Investigation purposes is used.

the one Energy of the electrons that are not converted into Bremsstrahlung is partially absorbed by the anode material and among others converted into heat. Therefore, the anode heats up when Operation of an X-ray tube to a high degree. The anode material should therefore expediently thermally stable so as not to be bombarded by electron bombardment to be destroyed or eroded. At the same time, the Thermal conductivity of the anode material as possible be high to the excess heat derive as effectively as possible. In particular, heat especially in the so-called focal spot on which the electron beam focused, generated. To point overheating in the focal spot To avoid high thermal conductivity is extraordinary important. The thermal conductivity thus helps to minimize the thermal load on the anode.

Also desirable is a good thermal shock resistance. Temperature change occur on the one hand when turning on and off the electrode beam of the cathode of the X-ray tube. On the other hand becomes the anode of the x-ray tube typically not permanently bombarded with electrons in a single focal spot, to a point thermal destruction of the anode in the focal spot to avoid. Instead, for example, so-called. Rotary anodes be used, which rotate around itself and thus the electron bombardment from a singular focal spot to a through the Distribute rotation resulting kerf. Or it can X-ray tubes are used in which the Electron beam during operation on changing points the anode is focused; an example are so-called Drehkolbenröntgenröhren, which rotate as a whole, and where a fixed x-ray beam is generated by the fact that the focal spot regardless of the rotation of the x-ray tube always at the same stationary point is generated. The constantly changing admission of the Anode by electron bombardment at alternating points of the anode also causes frequent temperature changes, so too Therefore, a high Temperaturwechselbelastbarheit desirable is.

One Material that meets the requirements explained above sufficient for practical use, is, for example, metallic tungsten (W). Therefore, in commercial available x-ray tubes usually metallic tungsten used as the anode material. The common embodiment is the rotary anode, the thermal load and wear of the anode material is minimized. Because rotary anodes for better cooling and heat dissipation made massive and voluminous are currently used mainly the backscattered Bremsstrahlung or laterally radiated Bremsstrahlung, wherein a lateral radiation through a special bevelled Form of the anode is achieved. A disadvantage of these embodiments is the low efficiency in terms of per electric power generated X-ray quanta. Much of the used Performance is converted into heat, which is also time-consuming must be dissipated.

From the publication DE 2653547 An anode is previously known which consists of thin tungsten plates. The generated X-radiation is not emitted laterally or backscattered, but instead emitted in a forward direction through the tungsten plate.

From the publication WO 96/29723 An anode is known in which the emitter layer consists of a thin layer of a high atomic number material, e.g. As tungsten, copper, molybdenum exists. It is arranged on a support (or substrate) with low absorption but good thermal conductivity, for. Berryllium, aluminum. The emitter layer is designed so that the material melts targeted at electron bombardment in the focal spot. Once the melting process begins, the electron beam is turned off and either the anode or the focus of the electron beam is moved so that the focal spot on the anode surface changes to another location. Then the electron beam is turned on again. In this way, the x-ray tube is used in a pulsed mode and every pulse hits a new spot on the anode.

The previously known emitter geometries in which the X-radiation is emitted in the forward direction, a achieve improved efficiency. However, due to the relatively thin emitter layer and relatively thin Carrier the risk of melting of the anode material relatively high. By a melting in the focal spot it comes to mixing between the material of the Emitter layer and the material of the carrier, resulting in a Degradation of the anode material leads. For example, you can form low-melting eutectics, which is a much lower Have temperature resistance, as the starting materials. This is especially true for the carrier materials Aluminum and berrylium, which may be typically provided.

Instead, however, carbon may also be chosen as the material for the carrier, since carbon, due to its low atomic number, only weakly absorbs the resulting forward X-rays as well as aluminum and beryllium. Particularly suitable are high temperature resistant and very good heat conducting graphite support, z. As pure graphite or carbon fiber reinforced graphite. Even with carbon, the materials of the emitter layer can form low-melting compounds when melting in the focal spot, z. B. can arise when using tungsten as the emitter layer W ₂ C and tungsten carbide (WC). Tungsten carbide already melts at temperatures between 1,400 ° and 2,000 ° Celsius, while pure metallic tungsten melts only at 3,422 ° Celsius. The same applies to molybdenum and tantalum. Therefore, emitter layers of tungsten, molybdenum or tantalum, especially if they are arranged on graphite carriers, are exposed to potentially high thermal wear, although they have extremely high melting points in pure form.

The The object of the invention is an anode and a corresponding X-ray tube and a corresponding X-ray device in which a degradation of the anode material and a concomitant deterioration of the temperature behavior prevented is.

The Invention solves this problem by an anode with the features of the independent first claim and by a X-ray tube and an X-ray machine with the features of the further independent claims.

One The basic idea of the invention consists in an anode for a X-ray tube comprising a support and an emitter layer, wherein between carrier and emitter layer a barrier layer is arranged.

By inserted between the carrier and the emitter layer Barrier layer can be mixed connections between the material prevents the emitter layer and the material of the carrier become. Instead, though, blends between the Material of the emitter layer and the barrier layer occur, with a suitable choice of the material of the barrier layer must However, these do not lead to degradation. If appropriate Choice of the barrier material can therefore a permanently stable temperature behavior the anode can be guaranteed. Such a concept Anode can with sufficiently thin emitter layers and Carriers will be built to move forward in an efficient manner operating mode to be operated. She can, however in a backward or sideways emitting Operating mode can be used advantageously.

A advantageous development of the basic idea is that the barrier layer mostly of one material there is no or the least possible inclination for the formation of chemical compounds or mixed compounds with the material of the wearer or for the installation of components of the material of the carrier, in particular of rhenium (Rh) or osmium (Os).

Thereby, that the material of the barrier layer has little or no connections received with the material of the wearer are in particular thermal adverse mixed compounds such as eutectics or peretectics or the like avoided.

A Another advantageous development is that the barrier layer mostly consists of a material that with Components of the material of the carrier mainly high-melting compounds forms, in particular with melting points above 4,000 K, in particular from hafnium (Hf).

Thereby, that the material of the barrier layer with the material of the wearer if necessary, high-melting compounds are involved, is a degradation avoided and the thermal melting behavior can even be improved become.

A further advantageous development is that the carrier consists largely of a material with a low atomic number, in particular with atomic numbers smaller than 14 , in particular of beryllium (Be, atomic number 4 ) or aluminum (Al, atomic number 13 ).

One Low atomic number material allows the passage of X-radiation, without absorbing them to a great extent. Therefore, it will allows an operating mode in which the X-ray radiation passes through the carrier and in the forward direction is emitted.

A further advantageous development is that the carrier consists largely of carbon (C, atomic number 6 ), in particular of graphite or carbon fiber reinforced graphite.

Graphite- and carbon fiber reinforced graphite have particularly high Temperature resistance and conduct heat particularly well. In particular, carbon fiber reinforced graphite is extraordinary stable. Because of the low atomic number of carbon is about it In addition, a largely absorption-free passage of X-radiation possible in the context of a forward-emitting operating mode.

Further advantageous developments are the subject of the dependent Claims or are in the following description of exemplary embodiments explained with reference to figures. Show it:

1 X-ray tube with fixed anode,

2 X-ray tube with rotary anode, and

3 X-ray machine.

In 1 is an x-ray tube 1 with fixed anode 3 shown schematically. The x-ray tube 1 includes a vacuum container 4 , which can be designed for example as a glass cylinder. Inside the vacuum container 4 are the essential components of the x-ray tube 1 arranged to generate X-rays.

A cathode 2 serves to generate electrons. It is located at one compared to the anode 3 strong negative potential. Due to the high potential difference between cathode 2 and anode 3 escaping electrons are accelerated towards the anode. The cathode may also be heated, either indirectly or through the current flowing through it, to promote the escape of electrons. An increase in electron yield can also be achieved by using field emitter cathodes, e.g. B. based on CNT (Carbon Nano Tubes) can be achieved.

The electron beam indicated by arrows in the figure is focused onto the anode by means of deflection coils. These are several coils or pairs of coils 5 . 6 intended. On the anode 3 the focused electron beam hits the so-called focal spot.

The anode 3 is above the X-ray exit window 7 arranged. The exit window 7 is part of the vacuum body 4 and is made of a high X-ray transmissivity material, e.g. B. Berrilium. Other embodiments of the exit window 7 may consist of other materials of high X-ray transmittance, ie with low atomic numbers, for example of aluminum or carbon.

The from the cathode 2 coming electrons first hit the emitter layer 10 the anode 3 on. The emitter layer 10 consists, at least predominantly, of a material of high atomic number, for example tungsten. Other materials with sufficiently high atomic numbers for the emitter layer 10 are copper, molybdenum or tantalum. The emitter layer 10 is in principle on the carrier 8th arranged at the same time the exit window 7 forms.

To a mixing of emitter layer with constituents of the material of the carrier 8th due to reflow upon severe heating by electron bombardment in the focal spot, is between emitter layer 10 and carriers 8th a barrier layer 9 arranged. The barrier layer 9 its purpose is to prevent such mixtures with the result of degraded thermal behavior.

For this purpose, for the barrier layer 9 either materials are chosen, the blends with the material of the carrier 8th prevent or at least greatly reduce. For example, rhenium or osmium can be used for this purpose. Or a material is used in which only mixtures are to be expected, which have a high or compared to the starting material even increased melting point. For this z. For example, hafnium, which would contribute to the formation of hafnium carbide (HfC) on a carbon support during melting, whose melting point of more than 3,890 ° C would be significantly higher than that of tungsten at 3,422 ° C. Hafnium carbide is the binary compound with the highest known melting temperature.

Additionally, the material becomes the barrier layer 9 chosen so that when melting in the focal spot and no mixed compounds with the material of the emitter layer 10 occur, which would cause a deterioration of the thermal properties.

The layer thicknesses of the exit window 7 , the barrier layer 9 as well as the carrier 8th are chosen so that in the emitter layer 8th generated X-rays, which is indicated in the figure by arrows, can pass through without strong absorption. The X-ray radiation is thus on the cathode 2 opposite sides of the anode 3 emitted in the direction of that of the cathode 2 coming X-ray beam, ie in the forward direction. For the emitter layer is preferably a layer thickness in the order of at most 10 microns selected, particularly advantageously on the order of three to five microns. For the wearer 8th , the same time the exit window 7 forms, preferably a layer thickness in the order of 100 microns is selected. It should be noted that on the one hand a possible absorption-free passage of X-rays should be ensured, which due to the low atomic number of the material of the carrier 8th or the exit window 7 is given, and that on the other hand, a sufficient mechanical stability must be ensured that the negative pressure in the vacuum vessel 4 withstand.

In 2 is a similarly designed x-ray tube 21 represented, however, unlike the above-explained a rotary anode 31 having. A cathode 22 is used to release electrons, which due to the high potential difference between the cathode 22 and the rotary anode 31 in the direction of the rotary anode 31 be accelerated, which is indicated in the figure by arrows. The electron beam is passed through several deflection coil pairs 25 . 26 on the rotary anode 31 focused in the focal spot.

In the focal spot, the electron beam first strikes the emitter layer 30 , which consists of one of the aforementioned materials of high atomic number. The emitter layer 30 is basically from the carrier 28 , worn here so the anode plate. The carrier 28 is made of a material of low atomic number, as explained above. To avoid mixing due to melting in the focal spot, lies between the emitter layer 30 and the carrier 28 a barrier layer 29 whose materials and functions are as described above, designed.

The layer thicknesses of the emitter layer 30 , the barrier layer 29 , as well as the carrier 28 are as also explained above chosen so that X-rays can pass largely without absorption. The transmitted, ie emitted in the forward direction, X-radiation passes through the X-ray emission window 27 from what is indicated by arrows. The X-ray exit window 27 exists as well as the carrier 28 made of a material of low atomic number to ensure low X-ray absorption. At the same time the layer thickness of the exit window 27 chosen so that one for the negative pressure in the vacuum tank 24 sufficient mechanical stability results.

To thermal overload in a consistent focal spot on the anode 31 is avoided during operation of the X-ray tube 21 the rotary anode 31 rotates, so that the focal spot on a so-called focal path on the rotary anode 31 emigrated.

In 3 is another embodiment with a sideways emitting X-ray tube 61 shown. The x-ray tube 61 includes a vacuum body 64 , which is intended for fixed installation in an X-ray machine. From the cathode 62 generated electrons are in the direction of a rotary anode 65 accelerated, which is indicated by arrows. The rotary gear 65 has a beveled area 66 on. The electrons become on the bevelled area 66 focused so that results in the focal spot on this. Due to the chamfer results for the emitted X-radiation sideways emission, which is indicated by arrows. The sideward emitted X-radiation passes through the side of the vacuum body 64 arranged X-ray exit window 67 therethrough.

In 4 is another embodiment with a sideways emitting rotary piston X-ray tube 51 shown. The rotary piston x-ray tube 51 includes a vacuum body 54 which is provided for a rotatably mounted installation in an X-ray apparatus. From the cathode 52 generated electrons are in the direction of an anode 58 accelerated. The anode 58 is fixed to the vacuum body 54 connected, so that during a rotational movement of the vacuum body 54 also the anode 58 rotated with this. The electron beam is transmitted through deflection coils 55 distracted, which is represented by arrows. The electron beam is deflected so that it is on a beveled area 59 the anode 58 is focused so that the focal spot on the beveled area 59 lies. Due to the chamfer results a sideways emission of X-rays by the entire vacuum body 54 circumferential X-ray exit windows 57 therethrough.

In operation, the rotary piston X-ray tube 51 during the electron bombardment of the anode 58 turned. As stated above, the anode rotates 58 together with the rotary piston x-ray tube 51 , At the same time, however, the electron beam is passing through the deflection coils 55 deflected so that the focal spot remains stationary regardless of the rotational movement of the rotary piston. Consequently, the anode rotates 58 through the focal spot. This results in the surface of the anode 58 instead of a punctiform focal spot, a burning trace, which allows selective overheating can be avoided. The fixed focal spot or focus of the electron beam simultaneously results in a stationary emission direction for the emitted X-ray radiation through the rotating X-ray emission window 57 ,

Suitable layer thicknesses for the carrier 8th . 28 can range from 0.1 mm to 3 mm. Suitable layer thicknesses for the barrier layer 9 . 29 may be in the range of 10 nm to 50 nm. Suitable layer thicknesses for the emitter layer 10 . 30 can be in the range of 1 to 10 micrometers, layer thicknesses of 3 to 5 micrometers can be particularly advantageous. For applying the layers, in particular the barrier layer 9 . 29 and the emitter layer 10 . 30 on the carrier 8th . 28 , conventional thin-film methods can be used, for. As sputtering, in particular magnetron PVD (Physical Vapor Deposition), or CVD (Chemical Vapor Deposition, vapor deposition). In particular, in view of the desired high layer thicknesses, more efficient deposition methods could be desirable, but for example, vaporization would be problematic because of the high melting points of the materials.

In 5 is an imaging X-ray machine 40 for medical diagnostics shown schematically. A so-called C-arm 41 carries the x-ray tube 42 equipped with an anode as previously explained. Next carries the C-arm 41 an X-ray image receiver 43 , The C-arm 41 is powered by a movable tripod 44 held by a controller 45 is moved to the desired position. A high voltage supply 46 represents the operation of the X-ray tube 42 required high voltage available. To examine a patient is a patient bed 47 provided on which a patient can lie to an imaging examination with the C-arm X-ray machine 40 to be subjected to.

A basic idea of the invention can be summarized as follows: The invention relates to an X-ray tube and an anode for an X-ray tube and to an X-ray device having such an X-ray tube. The object of the invention is to provide an anode and a corresponding x-ray tube and a corresponding x-ray device, in which a degradation of the anode material and a concomitant deterioration of the temperature behavior is prevented. A basic idea of the invention consists in an anode 3 . 31 . 58 . 65 for an x-ray tube 1 . 21 . 42 . 51 . 61 with a carrier 8th . 28 and an emitter layer 10 . 30 , where between carriers 8th . 28 and emitter layer 10 . 30 a barrier layer 9 . 29 is arranged. Through the barrier layer 9 . 29 can mixed connections between the material of the emitter layer 10 . 30 and the material of the wearer 8th . 28 be prevented. By suitable choice of material and mixed connections between the barrier layer 9 . 29 and the material of the wearer 8th . 28 or barrier layer 9 . 29 and emitter layer 10 . 30 are either prevented or lead to mixed compounds with respect to the starting materials equal to or higher melting points. This is a permanently stable temperature behavior of the anode 3 . 31 . 58 . 65 guaranteed. Such a thermally stable designed anode 3 . 31 . 58 . 65 can with sufficiently thin emitter layers or carriers 8th . 10 . 28 . 30 designed to operate in an efficient forward emitting mode.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 2653547 [0007]
• WO 96/29723 [0008]

Claims (13)

Anode ( 3 . 31 . 58 . 65 ) for an X-ray tube ( 1 . 21 . 42 . 51 . 61 ) comprising a support ( 8th . 28 ) and an emitter layer ( 10 . 30 ), characterized in that between supports ( 8th . 28 ) and emitter layer ( 10 . 30 ) a barrier layer ( 9 . 29 ) is arranged. Anode ( 3 . 31 . 58 . 65 ) according to claim 1, characterized in that the barrier layer ( 9 . 29 ) consists largely of a material which has no or minimal tendency to form chemical compounds or mixed compounds with the material of the carrier ( 8th . 28 ) or for incorporation of constituents of the material of the carrier ( 8th . 28 ), in particular of rhenium (Rh) or osmium (Os). Anode ( 3 . 31 . 58 . 65 ) according to one of the preceding claims, characterized in that the barrier layer ( 9 . 29 ) consists largely of a material that is compatible with constituents of the wearer's material ( 8th . 28 ) predominantly forms high-melting compounds, in particular with melting points above 4,000 K, in particular hafnium (Hf). Anode ( 3 . 31 . 58 . 65 ) according to one of claims 1 to 3, characterized in that the barrier layer ( 9 . 29 ) consists mostly of rhenium (Rh) or osmium (Os). Anode ( 3 . 31 . 58 . 65 ) according to one of claims 1 to 3, characterized in that the barrier layer ( 9 . 29 ) consists mostly of hafnium (Hf). Anode ( 3 . 31 . 58 . 65 ) according to one of the preceding claims, characterized in that the carrier ( 8th . 28 ) consists largely of a material with a low atomic number, in particular with atomic numbers less than 14, in particular beryllium (Be, atomic number 4 ) or aluminum (Al, atomic number 13 ). Anode ( 3 . 31 . 58 . 65 ) according to one of the preceding claims, characterized in that the carrier ( 8th . 28 ) mostly of carbon (C, atomic number 6 ), in particular of graphite or carbon fiber reinforced graphite. Anode ( 3 . 31 . 58 . 65 ) according to one of the preceding claims, characterized in that the carrier ( 8th . 28 ) has a thickness of from 90 microns to 3 millimeters. Anode ( 3 . 31 . 58 . 65 ) according to one of the preceding claims, characterized in that the emitter layer ( 10 . 30 ) consists largely of a material with a high atomic number, in particular atomic numbers greater than 28, in particular tungsten (W, atomic number 74 ), Copper (Cu, atomic number 29 ), Molybdenum (Mo, atomic number 42 ) or tantalum (Ta, atomic number 73 ). Anode ( 3 . 31 . 58 . 65 ) according to one of the preceding claims, characterized in that the emitter layer ( 10 . 30 ) has a thickness of at most a few micrometers, in particular of at most 10 micrometers. X-ray tube ( 1 . 21 . 42 . 51 . 61 ) with an anode ( 3 . 31 . 58 . 65 ) according to any one of the preceding claims. X-ray tube ( 1 . 21 ) according to claim 11 comprising a cathode ( 2 . 22 ) and an X-ray exit window ( 7 . 27 ), wherein the anode ( 3 . 31 ), the cathode ( 2 . 22 ) and the X-ray exit window ( 7 . 27 ) are arranged so that the X-radiation on the cathode ( 2 . 22 ) opposite side of the anode ( 3 . 31 ) is emitted. Imaging x-ray device ( 40 ) with an x-ray tube ( 1 . 21 . 42 . 51 . 61 ) according to one of the preceding claims 11 or 12.

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