X-ray tube with distributed filaments

An x-ray generating unit includes an x-ray tube that is substantially transparent to x-rays and that defines a vacuum therein. A cathode is disposed within the x-ray tube and defines a plurality of spaced apart cavities. An anode is spaced apart from the cathode and includes a material that emits x-rays when impacted by electrons. A plurality of filaments is each disposed in a different one of the cavities defined by the cathode and each is electrically coupled to the cathode. Each filament emits a focused electron beam directed to a different predetermined spot on the anode upon application of a predetermined voltage between the cathode and the anode, thereby causing the anode to generate x-rays.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to x-ray generating tubes and, more specifically, to x-ray tubes adapted for irradiating products.

2. Description of the Related Art

X-rays are used in a variety of applications such as imaging and product irradiation. Imaging applications include producing x-rays for computer aided tomography (CAT) scans. Irradiation applications include producing x-rays used to sterilize packaged food and other products. Imaging applications tend to require relatively less x-ray power than do high throughput irradiation applications.

Existing x-ray tubes include a hot or cold cathode, a filament (such as a tungsten filament in hot cathode embodiments) that is electrically coupled to the cathode, an anode that is spaced away from the filament and a target (such as a gold or tungsten target). In some embodiments, the anode also acts as the target. Certain x-ray tubes employ a very pointy cathode, without a separate filament, to generate electrons. Such cathodes are referred to as “cold cathodes.” The space between the cathode and the anode is substantially a vacuum. With sufficient voltage applied between the cathode and the anode, then the cathode (either cold or hot) will emit electrons which are accelerated toward the anode and strike the target, thereby generating x-rays.

The impingement of the electrons on the target generates heat. Any given x-ray power output from a single cathode will result in the generation of a certain amount of heat at this single location. Because of this, many x-ray tubes use a cooling system through which flows a coolant (such as water or an oil) to carry off heat or a rotary anode target. The tube is limited to a maximum x-ray output by the maximum amount of heat that can be concentrated at the single location on the target given the efficiency of the cooling system. Excessive heat can lead to the destruction of the anode as well as a loss of vacuum, leading to high voltage arcs.

Because the power output required for irradiation applications is limited by the amount of heat at the electron impingement point of the x-ray tube, such applications often require multiple tubes operating simultaneously to generate enough x-rays for successful irradiation or extensively long cycle times. Use of multiple tubes can be expensive and can require extra apparatus for powering, cooling and controlling all of the tubes. Long cycle times reduce overall throughput of the machine

Therefore, there is a need for a single high power x-ray tube for generating x-rays used in irradiation processes.

SUMMARY OF THE INVENTION

In one aspect, the invention is an x-ray generating unit that includes an x-ray tube that is substantially transparent to x-rays and that defines a vacuum therein. A cathode is disposed within the x-ray tube and defines a plurality of spaced apart cavities. An anode is spaced apart from the cathode and includes a material that emits x-rays when impacted by electrons. A plurality of filaments is each disposed in a different one of the cavities defined by the cathode and each is electrically coupled to the cathode. Each filament emits a focused electron beam directed to a different predetermined spot on the anode upon application of a predetermined voltage between the cathode and the anode, thereby causing the anode to generate x-rays.

In another aspect, the invention is an x-ray generator that includes an elongated linear x-ray tube, having a center, that is substantially transparent to x-rays and that defines a vacuum therein. The x-ray tube has a circular cross section. A cathode includes an elongated rod that extends along the center of the elongated tube and defines a plurality of spaced apart cavities. An anode is spaced apart from the cathode and includes a material that emits x-rays when impacted by electrons. The anode has an arcuate cross section that is less than 180°. A plurality of filaments, each disposed in a different one of the cavities defined by the cathode, each emit a focused electron beam directed to a different predetermined spot on the anode upon application of a predetermined voltage between the cathode and the anode, thereby causing the anode to generate x-rays. An outer tube is disposed about the x-ray tube and defines a gap therebetween through which a cooling fluid flows.

In yet another aspect, the invention is an x-ray generator that includes a toroidal x-ray tube, having a center, that is substantially transparent to x-rays and that defines a vacuum therein. The x-ray tube has a circular cross section. A circular cathode is disposed along the center of the toroidal x-ray tube and defines a plurality of spaced apart cavities. An anode is spaced apart from the cathode and includes a material that emits x-rays when impacted by electrons. The anode has an arcuate cross section that is less than 180°. A plurality of filaments are each disposed in a different one of the cavities defined by the cathode along a circular line running on one side of the circular structure. Each of the plurality of filaments is configured to emit a focused electron beam directed to a different predetermined spot on the anode upon application of a predetermined voltage between the cathode and the anode, thereby causing the anode to generate x-rays. An outer tube is disposed about the x-ray tube and defines a gap therebetween through which a cooling fluid flows.

DETAILED DESCRIPTION OF THE INVENTION

A preferred embodiment of the invention is now described in detail. Referring to the drawings, like numbers indicate like parts throughout the views. Unless otherwise specifically indicated in the disclosure that follows, the drawings are not necessarily drawn to scale. The present disclosure should in no way be limited to the exemplary implementations and techniques illustrated in the drawings and described below. As used in the description herein and throughout the claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise: the meaning of “a,” “an,” and “the” includes plural reference, the meaning of “in” includes “in” and “on.”

As shown inFIG. 1, one embodiment of an x-ray tube100includes a plurality of filaments112, each of which is disposed in a cavity114in a common cathode110. A target/anode120is spaced apart from the filaments112. When a sufficient voltage from a voltage source140is applied between the filaments112and the target120, the filaments112emit corresponding electron beams118that are focused by the cavities114. Typically, the filaments are connected in series to an activating voltage source142that applies a voltage across the filaments112to heat them as a result of resistance heating so as to reduce the work function in giving off electrons. The cavities114focuses an electron beam118from each of the filaments112to different spots on a target/anode120so that each spot on the target/anode120is separated from each other spot by a gap119that is not impacted by an electron beam118. Each of the filaments112generates electron beams114simultaneously in substantially the same amount. When the electron beams118hit the target120, the target120produces x-rays122. A vacuum tube130surrounds these elements and a vacuum is maintained inside the vacuum tube130. An external cooling tube132surrounds the vacuum tube130and allows a cooling fluid to flow around the vacuum tube130to remove heat therefrom. The tubes130and132can include any of the materials out of which x-ray tubes are typically made (e.g., glass, ceramics and certain metals).

The filaments112are distributed so that heat is generated at different locations on the target/anode120. As a result, the x-ray tube100can generate multiple times the power output of a single-filament x-ray tube using better cooling efficiency than the single-filament x-ray tube. For example, a four-filament system can generate the same amount of x-rays at each location on the anode as a single-filament tube—which cumulatively generates four times the x-ray power level as a single-filament tube, heating each electron impingement spot on the target to the same temperature as a single-filament tube, thereby increasing the cooling efficiency.

As shown inFIGS. 2A-2B, a toroidal embodiment of an x-ray tube200employs a toroidal vacuum tube230in which is disposed a circular cathode210to which several evenly spaced-apart filaments212are affixed. (FIG. 2Adoes not show the cooling tube for the sake of simplicity. The cooling tube232is shown inFIG. 2B.) X-ray emission radiates in all directions from the target220. The cathode shape and angle determine the location that the electron beam will hit on the target220.

As shown inFIG. 3A, one method of irradiating a product302includes passing the product202between two toroidal x-ray tubes200. This embodiment irradiates both sides of the product302simultaneously. As shown inFIG. 3B, in a second method of irradiating a product302, the product302is passed through a singlet toroidal x-ray tube200. This method can be applied when the product302is small enough so that it can fit inside of the toroidal x-ray tube200.

A spherical embodiment of an x-ray tube400is shown inFIGS. 4A-4B. Similarly, a domed embodiment may be used. In this embodiment, filaments430are distributed evenly about a portion of an outer surface of a spherical end424of the cathode420. Filament projections422can extend from the spherical end424and can define the focusing cavities for the filaments430. The target414is applied to an inner surface of the spherical portion of the x-ray tube410. A cooling jacket tube412surrounds the spherical portion of the x-ray tube410. This embodiment can generate x-rays that are distributed in the volume around the spherical portion of the x-ray tube410. This embodiment can apply x-rays to the inside surface of a hollow object or slurry.

The invention can include a linear cathode with the filaments spaced apart along a line. It can also include filaments that are distributed evenly around a cathode with a two-dimensional or three-dimensional shape, such as a toroid or a sphere.

One advantage of this system includes that it is able to generate a higher x-ray power level with the same form factor and about same cost as a prior art x-ray tube.

In one embodiment, each location of desired electron Emission has more than one filament but with only one as the active and the others as Spares. If a filament breaks or has undesired characteristics, a jumper on the tube in changed thereby activating one of the spare filaments instead. (More than one filament in a single location can also be activated at once if desired.)

In a typical embodiment used to irradiate objects does not include any shielded windows (of the type used in many imaging x-ray tubes) to allow a maximum amount of x-rays to irradiate the objects.

Although specific advantages have been enumerated above, various embodiments may include some, none, or all of the enumerated advantages. Other technical advantages may become readily apparent to one of ordinary skill in the art after review of the following figures and description. It is understood that, although exemplary embodiments are illustrated in the figures and described below, the principles of the present disclosure may be implemented using any number of techniques, whether currently known or not. Modifications, additions, or omissions may be made to the systems, apparatuses, and methods described herein without departing from the scope of the invention. The components of the systems and apparatuses may be integrated or separated. The operations of the systems and apparatuses disclosed herein may be performed by more, fewer, or other components and the methods described may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order. As used in this document, “each” refers to each member of a set or each member of a subset of a set. It is intended that the claims and claim elements recited below do not invoke 35 U.S.C. § 112(f) unless the words “means for” or “step for” are explicitly used in the particular claim. The above described embodiments, while including the preferred embodiment and the best mode of the invention known to the inventor at the time of filing, are given as illustrative examples only. It will be readily appreciated that many deviations may be made from the specific embodiments disclosed in this specification without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is to be determined by the claims below rather than being limited to the specifically described embodiments above.