US2850656A

US2850656A - X-ray tube structure

Info

Publication number: US2850656A
Application number: US457348A
Authority: US
Inventors: John P Lanefski
Original assignee: Machlett Laboratories Inc
Current assignee: Machlett Laboratories Inc
Priority date: 1954-09-21
Filing date: 1954-09-21
Publication date: 1958-09-02
Anticipated expiration: 1975-09-02

Description

p 2, 5 J. P. LANEFSKI 2,850,656

X-RAY TUBE STRUCTURE Filed Sept. 21, 1954 2 Sheets-Sheet 1 INVENTOR JOHN P. LANEFSKI l8 Flez BY g qgg ATTORNEY Sept. 2, 1958 J. P. LANEFSKI X-RAY TUBE STRUCTURE 2 Sheets-Sheet 2 Filed Sept. 21, 1954 FIG.3

INVENTOR.

JOHN P. LANEFSKI TORNEY States X-RAY TUBE STRUCTURE Application September 21, 1954, Serial No. 457,348

3 Claims. (Cl. 313-59) This invention relates to a novel X-ray permeable window for use in X-ray tubes. More specifically, this invention relates to an X-ray window which is bowed or corrugated in such a manner that it is able to change its shape in order to compensate differential expansion.

A high rate of failure of beryllium windows in certain types of X-ray tubes has been observed for some time. It has been found that changes in tube geometry will sometimes prevent destruction of the windows. However, changes in geometry also change characertistics in many instances, and often characteristics of the modified design are less desirable than those of the original.

My observations indicate that the principal cause of destruction of beryllium windows is the sudden, severe heating produced by bombardment of the windows by secondary electrons. More specifically, it is the nonuniform heating of various regions in the window and its support which results in the destruction. Beryllium is a material which has a relatively high expansion coefiicient and relatively low thermal conductivity. Consequently, regions removed from parts of the beryllium window which are heated by bombardment tend to become heated relatively slowly so that upon beginning tube operations extreme differences are encountered in the temperature of different regions in the window. In fact, it is possible for secondary electrons to generate a high surface temperature on the inside surface of the beryllium window while the rest of the window, including the outer surface, remains relatively cool for a period long enough for undesirable expansion effects to occur. Since the windows are rigidly fixed to the envelope structure in order to complete the vacuum envelope, the differential expansion which results will inevitably cause high internal stresses and possible deformation. If such is the case, the repetition of straining and relieving the strains during a period of use will cause cracks and fissures in the window and a consequent loss of vacuum.

My invention permits the relief of expansion-produced strains so that they will not cause window destruction. My invention permits adjustability in the window structure itself so that expansion effects may be relieved despite the fact that the window is rigidly affixed at all its edges to the relatively massive envelope structure. This adjustability is provided by shaping the window itself in such a manner that its expansion will merely exaggerate the shape which has already been provided in the window. Ordinarily, in accomplishing this end, the windown is convoluted in the same general pattern as the supported periphery of the window structure. For instance, when employing the invention with a conventional round disk window, the pattern of the convolution is circular wherein the circles are concentric with junction of the window and the support structure. In its simplest form, such a round window is providedwith a single slight bow in one direction or the other, but preferably extending away from the target. Despite the relative rigidity of its support at its periphery, which rigid support prevents outward expansion, such a w1ndow when atent G heated is able to absorb its expansion by increasing the gradient of the slopes of the convoluted or bowed part of the window. Thus, strains which would otherwise be produced by expansion are relieved without damaging the window structure.

For a better understanding of the present invention reference is made to the following drawings:

Fig. 1 illustrates in partial section an electron tube wherein one version of the present invention is employed;

Fig. 2 illustrates in cross-section a window construction of the present invention;

Fig. 3 illustrates schematically and in section an apparatus for forming the window structure shown in Fig. 2.

Referring to Fig. 1 an X-ray tube is illustrated wherein part of the vacuum envelope 10 is composed of a metal casing. The remainder of the envelope may be composed of glass or other suitable dielectric material through which leads from the cathode are brought out. Within the vacuum envelope are cathode 11 and anode 12. The cathode filament is not illustrated but is enclosed within the shielding and focusing member which is illustrated in elevation. The anode is a heavy copper block which, in this case, is kept at ground potential by directly coupling it to the envelope 10. Within the envelope the active surface of the anode is provided by a target block 13 of tungsten or other suitable dense material. The filament within focusing member 11 produces an electron focal spot on target 13. From this focal spot, in turn, originate X-rays which leave the vacuum envelope through beryllium window 14 in the end of the structure. Unfortunately, in addition to the X- rays, high energy secondary electrons are emitted from the target and impinge the beryllium window. These high energy electrons cause severe heating of the window and repetition of this heating in a conventional window may produce a recurrence of trains which will eventually cause breakage of the window. The window 14 is mounted in a pair of annular bezel members 15 which are fixed securely and vacuum tight to the metallic casing of vacuum envelope 10.

A casing 17 is provided to slip over the envelope portion 10. The space between the casing 17 and the envelope member is filled with insulating oil. Member 17 also provides a socket for connection to a terminal 19 on the end of cable 18. This terminal 19 may be partially viewed in Fig. l, but, for the most part, it extends inwardly into the socket provided for it in member 17.

As may be seen in Fig. 2, the X-ray permeable window 14 in accordance with this invention is provided with a slight convolution or bow in order to give it flexibility. This convolution or bow is located concentrically with the supported periphery of the window. Since the window 14 is located directly in the path of X-rays produced at target 13 and also in the path of secondary electrons, it is subjected to rapid heating to which its supporting structure is not subjected. This heating tends to produce expansion which, were no provision made to accommodate it,.would result in the build up of internal strains within the window structure. However, with the structure of the present invention expansion produces an increased bowing of window 14. In other words, the gradient of the bow increases or becomes exaggerated so that expansion is easily compensated.

An alternative construction of the window would be to make it corrugated with any number of convolutions arranged concentrically with the support for the window. The term convoluted shape is intended to include a single bow or multiple convolutions in a window.

The beryllium or other X-ray-permeable material may be formed into a window for use in accordance with this invention by the apparatus shown in Fig. 3. This apparatus is meant to be representative only and many other Patented Sept. 2, 1958 against platform .22 in such a manner that the bell jar maybeevacuated or -filled with a non-oxidizing gas. -Advantageously, the. structure basically consists of a pair ofv jaws generally designated 23 and Y24 between which the beryllium disk'25 to be formed is placed. Thejaws are the heating elements of a resistance heating system 7 which consis ts. of copper block members 27 and'28, stainless

steel die members

29 and 30 and

refractory memhers

31 and 32, of such material as graphite. The bottom copper block is made to fit a base piece 34 which holds it securely in place. The upper block 27 is urged downwardly' by spring member 35. 7 Electrical connections (not shown) :are employed to provide a current through the forming assembly. a

In operation of the assembly shown in Fig. 3 the region under the vacuum jar 21 is evacuated or filled with nonoxidizing atmosphere. Block 23 is acted upon by spring 35 and presses downward against disk 25 which it urges toward block 24. The spring pressure of spring 35 is sufiicient to urge the blocks into good electrical contact with disk 25 but not suflicient to deform the disk while cold. Current is then permitted to flow through the block. Because of the resistance encountered in

refractory material

31 and 32, the

die pieces

29 and 30 are heated and the heat is conducted to disk member 25. The heating is sufficient to soften the disk which then deformsunder the urging of spring 35 into the shape provided by the

die members

29 and 30. Inasmuch as pressure is retained on this disk until it is cool, the disk will retain the formed shape, as illustrated in Fig. 2, and may be employed in a tube assembly in accordance with the present'inv'ention.

' Die members of various shapes may be employed in order to obtain windows of shapes difierent from that illustrated in Fig. 2. Other changes in the apparatus and the geometry of the window illustrated will occur to those skilled in the art. All such changes or modifications Within the scope of the claims are intended to be within the scope and spirit of the present invention.

I claim:

1. An X-ray tube embodying an elongated housing containing a cathode and an anode and having in one end thereof an opening for exit of X-rays from the; anode, and within the opening a window formed of material having expansion characteristics different from those of the material of the housing adjacent the opening, the

window being of a metal relatively easily penetrated by X-rays and of relatively inflexible characteristics, the window further being a relatively rigid disclike member lying in a plane normal to the longitudinal axis of the. housing and having an annular. marginal, portion lying in said plane and vacuum-sealed throughout its periphery to the inner wallofthe opening, and further having its central portion integral with the annular marginal portion and formed with an outwardly bowed convolution whereby the central portion of the relatively rigid window may expand freely with respect to the housing.

2. An X-ray tube substantially as set forth in claim 1 wherein the window is beryllium.

3. An X-ray tube embodying a cylindrical housing containing a cathode and an anode and having in one end thereof a substantially circular opening for exit of X-rays from the anode, within the opening a relatively thick and rigid beryllium window having expansion characteristics different from those of the material of the housing, I

and an annular bezel vacuum-sealed throughout its periphery to the inner wall ofthe opening and having a groove formed in its inner peripheral edge, the window being a disclike member having a substantially planar annular marginal portion which is positioned within and vacuumsealed in the groove inthe bezel and further having its central portion integral with the annular marginal portionformed with an outwardly cupped shape whereby the central portion of the relatively rigid window may expand freely and unrestrictedly with respect to its supporting'structure. V

References Cited in 'the file of this patent Atlee Jan. 10, 1956 M rea -r