Embodiment variants of the present invention will be described in the following with reference to examples. The examples of the embodiments are illustrated by the following enclosed figures:
FIG. 1 shows a block diagram illustrating schematically an X-ray tube 10 of the state of the art. Electrons e− are thereby emitted from a cathode 20, and X-rays γ radiated from an anode 30 through a window 301.
FIG. 2 shows a block diagram, illustrating schematically the architecture of one embodiment variant of an X-ray tube 11 according to the invention. Electrons e− are thereby emitted by a transmission cathode 21, and X rays y radiated from an anode 31, the cathode 21 forming the cylinder barrel of a cylindrical tube core, and closing the vacuumized internal chamber 41.
FIG. 3 shows a block diagram, illustrating schematically the architecture of an embodiment variant of an X-ray tube 12 according to the invention. Electrons e− are thereby emitted from a transmission cathode 22, and X rays γ emitted from an anode 32, the cathode 32 closing the vacuumized internal chamber 42 toward the outside. The anode 32 is designed as a round or angular surface, and is irradiated by a transmission cathode 22 of laminar, reticulate, or linear form.
FIGS. 2/3 illustrate architectures as they can be used to achieve the invention. In these embodiment examples for an X-ray tube 11/12 with high dose rate, or respectively for a method for generating X rays with high dose rate, an anode 31/32 and a cathode 21/22 are disposed opposite each other in a vacuumized internal chamber 41/42. By means of impressible high voltage, electrons e− are accelerated to the anode 31/32 through the vacuumized internal chamber 41/42. In other words, the electrons are focused by the cathode 21/22 on a large surface of the anode 31/32 or on the entire anode 31/32, and generate X-ray radiation γ there. The vacuumized internal chamber 41/42 can be enclosed e.g. by a metal housing 52, for instance a cylindrical metal housing. The metal housing 52 can have e.g. a minimal wall thickness of 2 mm. It is likewise conceivable for the metal housing 50/52 facing the vacuumized internal chamber 41/42 to be electropolished and/or mechanically polished. The anode 31/32 and/or the cathode 21/22 can be electrically insulated by means of an annular and/or discoidal insulator 62. The insulator can e.g. be composed substantially of an insulating ceramic material. Conceivable as ceramic material is e.g. ceramic material of at least 95% Al2O3. Sintered on the ceramic can be a single or multiple layer of an alloy, for example. The alloy can comprise e.g. an MoMnNi alloy. Conceivable moreover is that the vacuumized internal chamber is enclosed by a ceramic housing, which at the same time insulates the cathode from the anode. The cathode 21/22 comprises a substrate substantially transparent for X-ray radiation γ. The cathode 21/22 can further comprise e.g. a thermionic cathode material (tungsten, tantalum, lanthanum hexaboride or barium mixed oxide) or a cold emitter. If the cathode 21/22 comprises a cold emitter, it can contain e.g. metal tips and/or graphite tips and/or carbon nano tubes. Through this configuration, the cathode 21/22 acts as the transmission cathode 21/22 for the γ-radiation. As mentioned, the substrate, such as e.g. Be (beryllium), Al (aluminum) or graphite, in particular pyrolytic graphite, is preferably as transparent as possible for X-ray radiation γ. According to the invention, the vacuumized internal chamber 41/42 of the X-ray tube 11/12 can be closed off by the transmission cathode 31/32 toward the outside, or respectively toward the inside, for example. The radiation goes through the transmission cathode 21/22, and behind it hits the material to be irradiated. The anode 31/32 comprises a layer of a metal with a high atomic number, e.g. gold and/or molybdenum and/or tungsten and/or a compound of the metals, allowing an efficient conversion into X-ray radiation γ. The anode 31/32 further comprises a cooling for cooling the thermal energy being created. The anode 31/32 must be cooled since typically only about 1% of the electric capacity is converted into X-ray radiation, and the rest must be given off as heat. The cooling can take place using water or with forced air. Through the configuration according to the invention, the entire radiation can be made use of in the outer half space. In contrast, in the conventional configuration, only about 10% of the radiation can be used in the half space (with 50° angle of opening of the window). A second advantage is that the area irradiated-by the electrons e− is considerably larger in the design according to the invention than in the conventional configuration. Assuming an irradiated area (anode) of 20×20 cm2 and a possible cooling capacity in this area of 200 W/cm2, there results a possible total electrical power of 80 kW, in contrast to 6 kW with the conventional tube. That is a further increase by a factor of 10. A transmission cathode 21/22 possibly absorbs, however, more radiation than a Be window in a conventional tube, depending upon the design. The output radiation is can <sic.> be thereby reduced by about half, depending upon wavelength. A dose rate increased overall by a factor of 50 still nevertheless results from this on a area of about 20×20 cm2, compared with the configuration with a conventional X-ray emitter. This increase in dosing capacity makes it possible, for example, to carry out sterilization with X rays in very short time periods.
FIG. 1 shows schematically an architecture of such a conventional X-ray tube 10 of the state of the art. Electrons e− are thereby emitted from an electron emitter, i.e. a cathode 20, as a rule a hot tungsten coil, are accelerated to a target through impressed high voltage, X rays γ being emitted from the target, i.e. from the anode 30, through a window 301. In other words, with the impingement of the electrons e− on the target, X-ray radiation γ is generated at the thus arising focal spot. The X-ray radiation emerges into the outer space through a window 301, and is used for irradiation purposes. Of the radiation generated on the target, only a small portion reaches the material to be irradiated. For reasons of geometry, the major part of the radiation is absorbed in the tube itself. For this reason, in order to irradiate the object completely, a particular irradiation spacing must be selected, depending upon the size of the object. In conventional configurations, typically, only about 10% of the radiation can be used in the half space of the target surface. FIG. 1 shows an emission window 301 with an opening of 50°.
FIG. 2 shows schematically the architecture of one embodiment variant of an X-ray tube 11 according to the invention. Electrons e− are thereby emitted from a transmission cathode 21, and X rays γ are emitted from an anode 31, the cathode 21 forming the cylinder barrel of a cylindrical tube core, and closing the vacuumized internal chamber 41. In other words, the X-ray tube 11 is designed as anode hollow cylinder 31 with a coaxial cathode hollow cylinder 21 inside. Anode 31 and cathode 21 can be achieved as described in more detail further above, for example. The electrons e− are accelerated from the transmission cathode 21 to the anode 31, and generate there X-ray radiation γ. The X-ray radiation γ penetrates the cathode 21 transparent for X-ray radiation γ. A uniform and very high 4π-gamma radiation, for example, can thus be achieved inside the cathode hollow cylinder 21. The material to be irradiated can be placed inside the cathode hollow cylinder 31. This ensures an even irradiation of the object from all sides, which would hardly be possible otherwise. This can be especially expedient for sterilization. It can be said that this embodiment variant is particularly suitable for sterilization with continuous conveyance of the material to be sterilized, and thereby for high throughput. A further advantage of this embodiment example is that since the anode does not have to be selected to be transparent for X-ray radiation, the cooling of the anode can be optimized compared with an embodiment variant with an anode transparent for X rays.
FIG. 3 shows schematically an architecture of another embodiment example of an X-ray tube 12 according to the invention. Electrons e− are thereby emitted from thermionic or cold emitters 72 in a transmission cathode 22, and X rays γ are radiated from an anode 32, the cathode 32 closing the vacuumized internal chamber 42 toward the outside. The cathode 32 is designed as a round or angular surface, the anode 32 being irradiated by the emitters 72 of laminar, reticular or linear design, for example. Like reference numeral 50, reference numeral 52 designates e.g. a metallic cylindrical housing 52, which comprises the vacuumized internal chamber 42, and reference numeral 62 designates an insulator, which separates the potential of the cathode and of the anode. It is also conceivable, however, for the housing 52 to be produced out of an insulating material, and for the insulator 62 to then be omitted. It is to be pointed out that the embodiment variants described by means of FIGS. 2 and 3 are especially intended for use of cold emitters, through the use of large-surface electron emitter configurations. Configurations with thermal cathodes are of course also conceivable, however.
Patent Application
20080049902
