US2836757A - X-ray generator target construction - Google Patents

Description

May 27, 1958 2. J. ATLEE X-RAY GENERATOR TARGET CONSTRUCTION Filed Feb. 11, 1957 INVENTOR. ZED J. ATLEE A T TORNEY5 2,836,757 Patented May 27, 1958 X-RAY GENERATOR TARGET CONSTRUCTION Zed J. Atlee, Chicago, 111., assignor to Dunlee Corp., Chicago, Ill., a corporation of Illinois Application February 11, 1957, Serial No. 639,350

Claims. (Cl. 313-330) The present invention relates to X-ray generators and more particularly to a new and improved anode structure for X-ray generators.

In making a radiograph wherein X-rays are generated by exciting an X-ray emissive element, generally termed a target element, with a beam of electrons, the object being radiographed is positioned between the source of X- rays and an X-ray sensitive medium so as to secure a shadow picture of the object. Obviously, the best definition in the picture would be obtained with a point source of X-rays. However, because of the heat generated by the impingement of electrons upon a target element, it is the practice to distribute the electrons over a relatively elongate rectangular area of the target and to tilt the target relative to the object being X-rayed so as to foreshorten the target area and, in effect, concentrate the X-ray source area. This is known as the line-focus principle.

To X-ray an object of relatively large area requires a source of greater intensity than is necessary for objects of lesser area, and, so that overloading of the target element does not occur, it is necessary in providing sources of relatively greater intensity to distribute the exciting electrons over a larger area than is required for forming sources of lesser intensity.

Now, many users of an X-ray generator have occasion for using X-ray sources of large intensity and other occasions for using a source of smaller intensity and of smaller effective area so as to secure shadow graphs of greater definition. To accommodate this dual demand, so-called double focus generators such as shown in my prior Patent No. 2,767,341 have been provided. The double focus generators provided heretofore have a pair of electron generating means capable of forming rectangular target areas of different size upon different portions of an anode target. Heretofore the target inclination to obtain the line-focus effect mentioned above has been the same for both portions of the target with the result that full utilization of the value of the linefocus principle has not been realized.

it is, therefore, an object of the present invention to provide a new and improved double focus X-ray generator.

A more particular object of the invention is to provide a new and improved X-ray generator anode.

A specific object of the invention is to provide an X- ray generator having means for providing a source of X-rays of relatively high intensity and further means for providing a source of lower intensity and concentrated area so that the generator may be used as desired for X-raying objects of relatively large thickness or area or alternatively for X-raying thinner objects or smaller areas with better definition.

Other objects and advantages will become more apparent hereinafter.

In accordance with the illustrated embodiment of the invention, I have provided an X-ray generator having a cathode unit including means for generating a pair of electron beams of rectangular cross section, The beams are focussed upon an anode target element having separate target portions for each beam. Both target portions are tilted so as to foreshorten the target area relative to an object being X-rayed, the target portion for the smaller beam being tilted so as to obtain a relatively greater foreshortening of the target area, thus providing a small, concentrated focal spot.

For a more detailed description of the invention, reference is made to the accompanying drawings wherein:

Fig. l is a side elevational view of an X-ray generator made in accordance with the invention;

Fig. 2 is a fragmentary view looking in the direction of the arrows 2-2 of Fig. 1;

Fig. 3 is an end View of the cathode of the generator, looking in the direction of the arrows 3-3 of Fig. 2;

Fig. 4 is an end view of the anode looking in the direction of the arrows 4-4 of Fig. 2;

Fig. 5 is a fragmentary, sectional view taken generally along line 55 of Fig. 1;

Fig. 6 is a sectional view of the anode taken along the line 6-6 of Fig. 4;

Fig. 7 is a sectional view of the anode taken along line 7-7 of Fig. 4;

Fig. 8 is a sectional view of the anode taken substantially along line 88 of Fig. 1; and

Fig. 9 is an enlarged, perspective view of the anode target element removed from the anode body. I

The present invention is illustrated in'connection with an X-ray generator comprising an envelope 10 of glass or other suitable material, a cathode unit 12 suitably mounted in one end of the envelope and a coaxial anode unit 14 suitably mounted in the other end of the envelope. The envelope 1% may be provided with a window portion 15 for the emission of X-rays.

Referring particularly to Fig. 3, the cathode unit 12 is preferably formed with two plane faces 16, 18 facing the adjacent end of the anode unit 14. The faces 16, it; are disposed at a large obtuse angle with respect to one another and intersect along a line 19 perpendicular to the longitudinal axis of the cathode head. .Formed in the face 16 is an elongated focussing cup recess 20 in which is mounted an elongated filament 22 for generating and focussing upon the anode face a rectangular electron beam 23. Formed in the face 18 isa smaller electron focussing cup 24 in which is mounted a shorter filament 26 for generating and focussing upon the facing end of the anode a rectangular electron beam 27 of smaller dimensions than the electron beam 23, as will be explained in greater detail hereinafter. The electron beams 23, 27 are focussed upon the anode with their longer cross sectional axes, indicated in Fig. 4 at 29, 31, respectively, substantially parallel. The filaments 22, 2e are connected to suitable leads indicated at 28 for connecting the filaments to a source of energy. 7

The anode unit 14 comprises a body 17 preferably formed of a metal relatively high heatconductivity such as copper. The end of the anode facing the cathode unit 12 is recessed or indented and embedded therein is a unitary re-entrant target element of tungsten or other metal of high atomic number formed with two planar face portions 32, 34 defining separate target areas for the electron beams 23, 27, respectively. A unitary rather than a two piece target element is preferred since in the case of a two piece target element the small strip of copper between the embedded pieces tends to overheat and penetrate or overfiow the edges of the target pieces, destroying their utility. Viewing the anode end as shown in Fig. 4, the electron beam 23 impinges on the target portion 32 over a rectangular area or focal spot 36 whereas the beam 27 impinges on the target portime 34 eve; a smallerrectan picture obtained,

'4 ar area or' focal spot 38.

Referring-particularly to-Eigseland-5, ina self-rectifying generator the face. portions .-;32,,34 of the target element 7 are preferably inclined at an angle A towards each other relativetoa plane perpendi'cnlarto the axis of the anode,

as -indicatedih Fig, 5, and -for the reasons set forthin my, p'rior Patent No. 2,767,341 The angle A may-be, for'example, '20 degrees, butit is to be understood that the {degree ofrinclinationis not critical and may be varied. It will be furthertunderjstood that in the case of generators-operated with direct current, the face portions 32,34 need not be inclined toward each other.

*-;In addition to 'being inclined toward one anotherythe target portions 32, 34 are each inclined at an acute angle with-respect to the cross sectional axis of the beam focussed thereon, ;and,-in accordance with the invention,

the a'ngles of incl-ination'of the target faces with respect to the beam focu ssed thereon are different from 'one another Inf the illustrated embodiment of the invention, the target portion 32 upon which the electron beam -23 is focussed isinclined'at an angle of 73 degrees with respect to the beam axis 29,-or at'an angle of 17 degrees with respect to aplane normalto the axis of the anode unit, as indicated in Fig. 7; As c omparedrto this, the

targetportion 34 is'inclined at an angle of 78 degrees 7 with respect to the axis 31 of the electron beam 27, or

at angle of 12 degrees with respect to a plane normal to the axis of the anode unit as indicated in Fig-6;

These angles-are, of course, tobe taken as merely illustrative and it is tobe understood'that the angles of inclination may be varied to meet'the conditions desired. To better illustrate the relation of the target portions velope axis and substantially parallel to the direction of the cathodefilamentsyand through the envelope window l5. Thus, viewed from the object being photographed, the target areas 36, 38 are each foreshortened, as shown in-Fig. 2, to a small, nearly square, rhombus.

It will be appreciated that, though as mentioned before apoint source is theoretically the ideal, a square or nearly square source'of X-rays is the preferred practical configuration'in an X-ray generator of the class described so as to 'obtain the best. possible definitionin the shadow ,Itwill also be apparent that to X-ray a large area ,will require more X-raysthan would be required to X-ray a'smaller area. 'While a single source may be utilized to X-ray Iarge and small areas by varying the total time of exposure, this is not desirable for various reasons which.

need not be. mentioned here. Instead it is preferred to provide ardouble focus generator such as shown in'my prior Patent No. 2,767,341, mentioned previously, which maybe operated to provide a small source of X-rays capable of generating a given number. of X-rays per unit of time for X-raying a small area, or to provide a larger of the target were then established. This generallyjre sulted-in-providing--an angle of tilt on -thetargetof-be-' tween about 17' degrees to 20 degrees. I

Next the shape of the smaller target area was considered. With the desired intensity of the smaller source established, the necessary shape of the target area to obtain the smallest possible square, i. .e., rhombic, projection was determined. "'A principal advantage of, the present invention arises at this point, for with the steeper angle of tilt provided in a generator of the invention, the target'area for the small focal spot can be so shaped as to produce a smallerprojection capable of producing the same number of X-rays as compared to the size of the projection of the smaller target areas which could, be secured in the generator construction heretofore employed. This is becausethe steeper. positioning of the target portion 32 results in greater foreshortening of the projection of the focal spot toward the object being. X

rayed. a consequence, the focal spot38 may" be made relatively narrower than could be done in thecase of generators as designed heretofore. Therefore, it"is.

possible with thegenerator of the invention to secure -X-ray'shadow"graphs, with better detail becausefofthe V smaller-size of-the'focal spot 38. j i "This-is'of extreme value, for example, to radiologists making X-ray examinations of parts of thetbod y. "Inmaking the initial exploratory examinations, the genershadow graph of the area in question with greater detail.

Similar advantages accrue to other. users of the invention.

Having illustrated and described a preferred embodiment ofthe invention, it should be apparent to those skilled in the art that the inventionpermits of modification in arrangementand detail. I claim, as my invention all such modifications as come within the true spirit and scope of the appended 'claims.

I claim:' r

1. An X-ray generator comprising cooperating anode and cathode units facing each other in spaced apart relation, said cathode unit having a pair of laterally spaced apart electron generating means for generating and focussing a pair of substantially parallel beams of electrons upon the facing end of said anode unit with said beams each having a rectangular cross section but being of differentcross sectional length with the longercross sectional axes of the beams substantially parallel to one another, said anode unit having a unitary target element isf ocus'sed being inclined at an angle of about 12 degrees with respect to the longer cross sectional axis of the beam focussed thereon, the other of said face portions being inclined at an angle of about 17 degrees with respect to source capable of generating a larger number of .X-rays for the same unit of time for X-raying larger areas and also capable of generating more intense X-rays for X-ray- 7 ing thicker bodies.

. The double'focus generators provided heretofore have had the same angle of tilt provided for the target portions for both the large and the small focal spot, but the angle of tilt has; been largely determined'by the requirement to-get a square projection of the large focal spot. Indesigning the generator/the intensity desired for the larger source was first decided. Having decided the intensity of the source, the most ideal angle of tilt and theshape of thetarget area to obtain the. smallest possible .square .projectignlwithfthe..maximurrr safe loading the longer cross sectional axis of the beam focussed thereon a i 2. An X-ray generator comprising cooperating anode and cathode units facing each other in spaced apart relation, said cathode unit having a pair of laterally spaced apart electron generating means for generating and tron bearns, one of said face portions being inclined at an angleof about 12 degrees with respect to the longer cross sectional axis of the beam focussed thereon, the other of said faceportions being inclined 'at an angle of abont 17 degrees with respect to the longer cross sectional axis of the beam focussed thereon.

3. An X-ray generator comprising cooperating'anode and cathode units facing each other in spaced apart relation, said cathode unit having a pair of laterally spaced apart electron generating means for generating and focussing a pair of substantially parallel beams of electrons upon the facing end of said anode unit with said beams each having a rectangular cross section and with the longer cross sectional axes of the beams substantially parallel to one another, said anode unit having a unitary target element having two planar face portions each defining separate target areas for each of said electron beams, each of said face portions being inclined at an acute angle with respect to the longer cross sectional axis of the beam focussed thereon, the angle of inclination of said face portions being different from one another.

4. An X-ray generator comprising cooperating anode and cathode units facing each other in spaced apart relation, said cathode unit having a pair of laterally spaced apart electron generating means for generating and focus sing a pair of substantially parallel beams of electrons upon the facing end of said anode unit, with said beams each having a rectangular cross section but being of different cross sectional lengths, said anode unit having two planar faced target element portions each defining a separate target area for one of said electron beams, said face portions being inclined at small acute angles with respect to the longer cross sectional axis of the beams focussed thereon, the face portion upon which the beam of the smaller cross sectional length is focussed being inclined at a steeper angle relative to the cross sectional axis of said beam than the angle of inclination of the other face portion relative to the cross sectional axis of the beam focussed thereon.

5. An X-ray generator comprising cooperating anode and cathode units facing each other in spaced apart relation, said cathode unit having a pair of laterally spaced apart electron generating means for generating and focussing a pair of substantially parallel beams of electrons upon the 'facing end of said anode unit, with said beams each having a rectangular cross section, said anode unit having a unitary target element having two planar faced portions each defining a separate target area for one of said electron beams, each of said face portions being inclined at a small acute angle with respect to the longer cross sectional axis of the beam focussed thereon, the angles of inclination of the face portions relative to the corresponding cross sectional axis diifering on the order of 5 degrees.

References (Iited in the file of this patent UNITED STATES PATENTS 2,767,341 Atlee Oct. 16, 1956

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