US2896105A - High capacity x-ray tube - Google Patents

Description

July 21, 1959 R. HOSEMANN HIGH CAPACITY X-RAY TUBE Filed Jan. 2, 1957 Fig.2

Inventor? ou HOSEMANA/ By ,MM

A Ilorneys United States Patent HIGH CAPACITY X-RAY TUBE Rolf Hosemann, Berlin-Grunewald, Germany Application January 2, 1957, Serial No. 632,322

8 Claims. (Cl. 313-56) The present invention relates to high-capacity X-ray tubes. More in particular, the present invention relates to high-capacity X-ray tubes for the purposes of radiotherapy and food preservation.

It is known that a radiation of high intensity is needed for the purposes of radio-therapy and food preservation. All known types of X-ray tubes, however, produce only radiation of a limited intensity. A further increase of the dosage yield of these types of X-ray tubes is checked by the unavoidable production of heat at the surface of the anode target whereupon the electrones emitted by the cathode impinge. Under normal conditions not more than kw. are attained. A further increase of this yield up to 50 kw. and higher can only be reached if X-ray tubes are used which are equipped with rotating anodes and wherein the excessive heat produced at the target is dissipated by water cooling.

These X-ray tubes are, however, extremely complicated both in regard to their construction and maintenance and are hence very expensive to build and to operate.

It has now been observed that for many'applications of X-rays in radio-therapy it is not necessary to produce a focal spot having the usual small area of but a few cmfi. Particularly for the purpose of food-preservation an X-ray tube producing a focal spot having a much larger area would be quite sufiicient.

On the other hand, focal spots having an area larger than the usual area cannot be produced with conventional X-ray tubes. The types of anodes used in the known X-ray tubes would. necessitate the construction of undesirably bulky tubes, if adopted to produce'large focal spots. The known types of X-ray tubes also suffer from the disadvantage that only a fraction of the X-rays produced at the anode emanates from the windows of the X-ray tube.

With the foregoing in mind, it is the general object of the present invention to provide for a high capacity X-ray tube which is specifically adapted to the particular needs of radio-therapy and food preservation.

It is another object of the present invention to provide for a high capacity X-ray tube with a large focal spot.

It is a further object of the present invention to provide for a high capacity X-ray tube having a comparatively simple construction, and which is uncomplicated and easy to maintain and which is at the same time comparatively inexpensive.

It'is still another object of the present invention to provide for a high capacity X-ray tube where a substantial amount and up to 50% of the X-rays emanate from the window of the tube.

It is still a further object of the present invention 'to provide for a' high capacity X-ray tube where the X-rays penetrate substantially the entire area. of the window of the tube.

' It is still another object of the present invention to provide for a high capacity X-ray tube wherein the stream of electrons radially emitted from the cathode ischannelled towards the anode-target.

These objects are achieved by the new high capacity X-ray tube of my invention which is based on the type of X-ray tubes having an anode assembly comprising a Wehnelt-cylinder drum, further comprising a hot cathode, and in which at a total load of the anode of at least two kw. the anode is given the form of a membrane which simultaneously serves as the ray-transmissive window of the tube. The anode heat created at the anode membrane by the impinging electrons is dissipated by cooling the anode from outside. According to the present invention this X-ray tube is so constructed that the specific electric load across the entire area of the window assumes a substantially constant value of not more than 40 watt/mmfi. As the membrane-anode functions simultaneously as the ray-transmissive window of the tube, almost half of the X-rays produced at the drum anode reaches the outside.

While anode assemblies comprising a 'drum cylinder are known in the art, these known types of X-ray tubes produce only a very small focal spot and the yield of the tube therefore does not substantially exceed 2 kw. According to the present invention the form of the hot cathode and the Wehnelt-cylinder are so chosen that a largefocal spot is created upon the anode and the entire area of the ray-transmissive window is evenly covered with a regular density of the electron stream.

The invention will be better understood by the following detailed description of the accompanying drawings in which like reference numerals designate like parts and wherein' Figure l is a cross sectional view of the X-ray tube of the invention;

Figure la is a cross sectional view of the heating filament of the cathode forming a part of the X-ray tube shown in Figure 1;

Figure 2 is a cross sectional view of a preferred embodiment of the X-ray tube of the invention;

Figure 2a is a cross sectional view of the heating filament of the cathode forming a part of the X-ray tube shown in Figure 2;

Referring now to the drawings somewhat more in detail, the glass basis 1 of the cathode encloses and sup ports the supply wires 2, 3 for the heating filaments 5 and 6, respectively and the support wire 4 for the Wehnelt-cylinder 20. In the embodiment shown in Figure l of the drawings the cathode consists of an outwardly bulged flat spiral 5 having a surface like a spherical calotte. The Wehnelt-cylinder 20 circularly encloses this calotte all around in such a manner that the equipotential surfaces 8 assume the shape of a spherical calotte only in the immediate vicinity of the heating filament whereas they are flattened starting with their respective edges in the direction of the anode due to the influence of the Wehnelt-cylinder 20. The electrons projected from the hot filament first are shot in all directions; however, at the edges of the equipotential surfaces 8 they are increasingly concentrated and directed along a central ray and are thus channelled towards the anode-target.

The drum anode consists of a disk shaped membrane 9 which is vacuum tightly fitted against the casing wall 21 so as'to form one uninterrupted and uniform structure with the latter. Since the voltages employed exceed 80 kv. and only hard rays are created the membrane 9 may be composed of copper or fernico-sheet metal having a thickness of approximately 2 mm. In that case the wall' constituting the drum anode is simultaneously used as a preliminary filter. The wall 21 is joined to the cathode portion at 19 by a glass fusion, the joint being screened electrostatically by the metal cylinder 25. Against the inner side of the anode within the range of the window there is welded a thin sheet 10 of a heavy metal. An

other, water-tight wall 17 surrounds the anode portion of the X-ray tube of the invention. This wall 17 may be composed of material having a light atom weight as, for instance, plastics. Thereby, the absorption, of useful X-rays can be reduced. The cooling liquid 13 is supplied and abducted through the tubular protrusions 14 and 15 adapted for a rubber connection.

Due to the above described field distribution in the interior of the X-ray tube the electrons emitted by 'the hot filament-cathode hit the anode sheet metal at an almost uniform and even energy density. The window frame 21 although also being cooled by the cooling liquid 13 is subjected to but a fraction of the density of radiation hitting the anode sheet metal 10. 3 Figure 2 shows a preferred embodiment of the present invention, in which the anode rather'tha'n being of the type of a circular drum anodeformspart ofa cylinder surface 11. a

The axis of this cylinder having a surface 11 extends vertically to the plane of the drawing of Figure 2. The hot cathode is composed of several, spirals 6 located parallel to the cylinder axis and having axes upon a cylinder surface which is situated concentrically relative to the first mentioned cylinder. 20 confines the radially extending parts of the electrons. As a consequence, only few electrons hit the window frame 21 while the bulk of theelectrons hit the anode target.

The Wehnelt-cylinder The anode window 11 is reenforced and mechanically stabilized by a plurality of reinforcing portionsor ribs 12 which are located parallel to the cylinder axis belonging to the cylinder having surfaces 11. The ribs are applied to the anode window 11 at the vacuum side of the latter and thus divide thesame into several partial cylinders. The anode window and the ribs may be both constructed of one piece of metal. At the vacuumside this thin metal sheet can be covered with a thin layer of a metal having a heavy atomic weight. Within each partial window defined by the ribs 12 the density of the electron stream emitted by the heating spirals 6 and impinging upon the anode-window is sub stantially constant. The heating spirals are arranged at a distance from each other, and therefore there is an intermediate space with a low density of the electron stream between the two neighboring electron streams 23, 24 produced by two neighboring spirals of the heating spirals 6. The ribs 12 are located in the range of this intermediate space of low density of the electron stream. Therefore the specific surface load of the partial windows 11 can be fully utilized without subjecting the less intensely cooled ribs 12 to the danger of evaporizing under the impact of heat created by the impinging electrons. As set forth above, a tube of this type is designedfor a load of at least 2 kilowatts and the specific load on the anode should be not more than watts/mm. Consequently, the total area of the anode, exclusive of thetreinforcing ribs, is at least mmF. a

The number of ribs and thereby the number of partial windows as well as the number of heating spirals can of course be varied. Howevenpreferably the number of heating spirals corresponds to the number of partial windows so that there is a heating spiral for each partial window, the latter being defined by two ribs.

The cooling liquid circulates between the windows '11 V and the water-tight, cylindrical exterior wall 18. At the points indicated in Figure 2'of the drawings'by'the small crosses 16 every partial window may be equipped with its own tubular-protrusions adapted for a rubber connection similar to those designated by reference numerals 14 and 15-of Figure l for supplying and abducting the cooling liquid 13. The ribs may'slightly protrude into the vacuum space of the X-ray tube. In order to increase the mechanical stabilization of the'anode window 11 theribs 12.can also be extended down to the exterior wall 18 (not shown). In that 'case the anode window can be inserted mm. so that at a total load from the outside. The anode window can also be composed of several pieces and these pieces can be inserted in the tube structure from the outside so as to form the anode window.

The heating spirals 6 are switched in parallel or in series by the wires 7. All other features of this embodiment are analogous to the features described in regard to the basic embodiment of the invention shown in Figure l of the drawings.

It is also possible to combine the embodiments shown in Figures 1 and 2, respectively. For example, the raytransmissive anode window may have a disk shaped configuration bulged outwardly in the form of a spherical calotte or, the rib-'nforced window of the embodiment shown in Figure 2 may be made planar rather than being bulged outwardly.

It will be understood that this invention is susceptible to modification in order to adapt it to different usages and conditions, and, accordingly, it is desired to comprehend such modifications within this invention as may fall within the scope of the appended claims.

What I claim is:

1. A high-capacity X-ray tube comprising, in combination, drum anode means incorporating a membrane which is ray-transmissive and serves as the ray-transmissive window of the X-ray tube, and which membrane is formed with reinforcing portions, and ray-transmissive means located outwardly of said membrane and forming therewith a cooling chamber adapted to receive a coolant; and cathode means for directing electrons toward substantially the entire area of said membrane except said reinforcing portions thereof, said membrane exclusive of said reinforcing portions, having an area of at least 50 of at least two kilowatts the specific electric load across the entire area of said membrane, except at said reinforcing portions thereof, assumesa constant value of not more than forty watts per square millimeter. v

2. A high-capacity X-ray tube comprising, in combination, drum anode means incorporating an inner membrane which is ray-transmissive and serves as the raytransmissive window of the X-ray tube, and which inner membrane is formed with reinforcing portions that divide the surface area of said inner membrane into a plurality of membrane-portions, and a ray-transmissive outer membrane spaced outwardly from said inner membrane and forming therewith a cooling chamber adapted to receive a coolant; and cathode means comprising a plurality of cathode elements equal in number to the number of membrane portions and positioned for directing electron beams toward said plurality of membrane portions,.respectively, so that electrons are directed toward substantially the entire surface area of said inner membrane with no electrons being directed toward said reinforcing portions, said plurality of membrane portions having a total area of at least fifty square m'llimeters so that at a total load of at least two kilowats the specific electric lo'ad across the entire area of said inner membrane, except at said reinforcing portions thereof, assumes a constant value of not more than forty watts per square millimeter. f r

3. A high-capacity X-ray tube comprising, in combination, drum anode means incorporating an inner membrane which is ray-transmissive and serves as the ray transmissive window of the X-ray tube, and which inner membrane is formed with reinforcing ribs that divide the surfacegarea of said inner; membrane into a plurality of membrane portions, and. a ray-transmissive outer membrane spaced outwardly from said inner membrane and forming therewith a cooling chamber adapted to receive a coolant; and cathode means comprising a plurality of cathode elements equal in number to the number of membrane portions and positioned for directing electron beams toward said plurality of membrane portions, respectively,

trons being directed toward said reinforcing ribs, said plurality of membrane portions having a total area of at least fifty square millimeters so that at a total load of at least two kilowatts the specific electric load across the entire area of said inner membrane, except at said reinforcing ribs thereof, assumes a constant value of not more than forty watts per square millimeter.

4. A high-capacity X-ray tube as defined in claim 3 wherein said inner membrane is concave.

5. A high-capacity X-ray tube as defined in claim 4 wherein said ribs project from the inner surface of said inner membrane into the interior of the X-ray tube.

6. A high-capacity X-ray tube comprising, in combination, drum anode means incorporating a concave inner membrane which is ray-transmissive and serves as the raytransmissive window of the X-ray tube, and which inner membrane is formed with reinforcing ribs that extend substantially parallel to each other and divide the surface area of said inner membrane into a plurality of strips, and a ray-transmissive outer membrane spaced outwardly from said inner membrane and forming therewith a cooling chamber adapted to receive a coolant; and cathode means comprising a plurality of substantially parallel elongated filaments which extend in the direction of said strips, said filaments being equal in number to the numher of surface strips and being so positioned that each filament directs an electron beam toward a corresponding surface strip so that electrons are directed toward substantially the entire area of said inner membrane except said reinforcing ribs thereof, said inner membrane being so dimensioned that at a total load of at least two kilowatts the specific electric load across the entire area of said inner membrane, except at said reinforcing ribs thereof, assumes a constant value of not more than forty watts per square millimeter.

7. A high-capacity X-ray tube as defined in claim 6 wherein said filaments are arranged along an arcuate path which is substantially coaxial with said concave inner membrane.

8. A high capacity X-ray tube as defined in claim 7 wherein said cathode means further include a Wehnelt cylinder.

References Cited in the file of this patent UNITED STATES PATENTS 1,657,292 Williamson Ian. 24, 1928 2,107,520 Schade Feb. 8, 1938 2,517,260 Van de Graalf et a1. Aug. 1, 19 50

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