US3135889A

US3135889A - Protected window x-ray tube

Info

Publication number: US3135889A
Application number: US196837A
Authority: US
Inventors: Jack A Soules
Original assignee: Individual
Current assignee: Individual
Priority date: 1962-05-22
Filing date: 1962-05-22
Publication date: 1964-06-02
Anticipated expiration: 1981-06-02

Description

June 2',

JACK- A; soULEs June 2, 1964 Filed May 22, 1962 J. A. SOULES PROTECTED WINDOW X-RAY TUBE 2 Sheets-Sheet 2 INVENTQR JLMZK A. SOU LES United States Patent O 3,135,889 PRGTECTED WINDW X-RAY TUBE .lack A. Seules, Arlington, Va. (Box l6i5, University Park, N. Mex.) Filed May 22, 1962, Ser. No. 196,837 3 Claims. (Cl. B13- 59) (Granted under Titi-e 35, US. @ode @952), sec. 255) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

r'he present invention relates to X-ray tubes useful as a source of soft X-rays and more particularly to a means for protecting the window of an X-ray tube usable in a high vacuum system.

Heretofore most usage of X-rays has been in the hard X-ray range below l angstroms which penetrate the subj ect being examined. More and more emphasis is being placed on research or studies which make use of the soft X-ray region between and 100 angstroms, in which the X-rays have a low penetrating power. The hardness of X-rays produced by an X-ray tube depends on the impressed voltage, and the amount of useful X- rays emanating from the tube depends on the exit window. Thick windows absorb most soft X-rays produced, therefore soft X-ray production requires very thin windows. Also, an extremely high vacuum is required in an X-ray tube to provide a clean anode and therefore a uniform and constant X-ray spectral distribution. Pressure dilerentials between the X-ray tube and the surrounding medium require suciently thick windows to prevent breakage thereof. Therefore, the production of soft X-rays depends strongly on the window which can be used in the X-ray tube, and the type of material and thickness of the tube window, as well as the X-ray tube, depends on their ability to withstand the high temperatures and vacuum pressure experienced in degasifying the metal parts within the tube and subsequent operation of the tube for continuous operation.

Heretofore, X-ray tubes have been used for spectrographic or crystalline analysis in which the X-ray tube and the vacuum chamber, in which the X-rays are used, are made into one integral system. In such a system, the X-ray tube and vacuum chamber are operated at the same vacuum pressure. This has the disadvantage that the X-ray anode cannot be kept clear and the spectral distribution is generally not uniform or constant.

The X-ray tube of the present invention makes use of a gate valve in combination with an X-ray tube which has a very thin tube window. The combination can be used to produce soft X-rays and to protect the window against damage if the tube is removed from the vacuum system within which the tube is normally used. The combination also permits evacuation of an X-ray tube to an ultra-high vacuum pressure of about l09 mm. Hg and baking of the combination at very high temperatures during degassing of the tube. Further, the combination permits operation of the X-ray tube at a pressure different from that of the vacuum system or chamber within which the X-ray tube is used.

It is therefore an object of the present invention to provide a soft X-ray tube with a means for protecting the window of the X-ray tube.

Another object is to provide a means by which an X- ray tube having a very thin window can be evacuated to an extremely high vacuum in atmospheric pressure.

Still another object is to provide an X-ray tube which will withstand high temperature during degassing or use without deleterious effects on the tube window.

Yet another object is to provide an X-ray tube with a protected window.

l Patented .lune 2, 1964 While still another object is to provide an X-ray tube operable in a vacuum system in which the pressure in the tube is much lower than that of the vacuum system within which the X-ray tube is operated.

The nature of this invention as well as other objects and advantages thereof will be readily apparent from consideration of the following speciiication relating to the annexed drawings, in which:

FIG. l is an exploded view shown in perspective which illustrates the relative parts of the invention;

FIG. 2 is a side View partly cut away to better illustrate the parts; and

PEG. 3 is an end view of the gate valve assembly.

Now, referring to the drawings, there is shown by illustration an X-ray tube l@ provided with a metal envelope ll, or any other suitable material, comprising a cathode unit l2 and an anode unit 13 positioned relative to each other and adjacent to an X-ray exit window 14. rihe anode comprises a suitable target such as tantalum molybdenum or tungsten to provide an X-ray source which is directed through a very thin foil window i4 of A1203 or other low X-ray absorbing material. The window is sealed in a special opening in one end of the tube which is formed with a sharp, shaped, right angular corner l5. The X-ray tube is provided with an electrical source of less than 10,000 volts, not shown, for simplification of the drawings, suitable for producing soft X-rays having wavelengths between two and one hundred angstrom units. The tube is also provided with suitable means for securing the cathode and anode in place and is provided with a tubular passage i6 to the anode through which water is forced to cool the anode during use. The base 17 of the X-ray tube is larger in diameter than the envelope and is provided with right-hand threads 18 of about thirty-two threads to the inch on the outer edge to which one end of a coupling 19 is secured by screw threads. The coupling 19 is provided with holes 20 therein within which a Spanner wrench fits to rotate the coupling. One end of a stainless steel bellows 21 is secured to the base between the envelope and the coupling and extends therebetween along the envelope.

A gate valve assembly 22 is secured within a housing having a cylindrical portion including a threaded end 23 which is provided with twenty-four threads to the inch and an outwardly extending rirn 24 with the cylindrical portion extending to an integral front Wall 25 which is a continuation of the ridge and which is provided with a central aperture 26. The gate valve assembly 22 is secured in the housing by suitable bolts 29 and includes a cylindrical structure Si) with a somewhat semicircular opening in the upper portion and solid portion at the bottom. The opening in the top portion is sufficiently large to receive therein a gate valve 27 of semicircular shape which has a radial upward movement sufficient to clear the central aperture 26 in the front wall of the housing and the X-ray exit window of the tube and a sulficient downward movement to entirely cover the aperture 26 and the X-ray exit window. The gate valve 27 can be made of copper or any other suitable material and is provided with parallel passages therein through which guide rods 28 are passed to secure the gate valve for radial movement within the gate valve assembly. The guide rods 2% are passed through the upper wall of the assembly and extended vdownwardly into the solid bottom portion of the circular structure Sil and secured therein by screw threads or any other suitable manner. The gate valve is moved relative to the guide rods by a draw rod 3l which passes through an aperture in the circular structure 30 and then through the ridge of the housing. The gate valve is moved parallel to the front wall of the housing and can be moved to a position above the X-ray tube methods, one of which will be explained.

3 window and the aperture in the housing and when lowered, the gate valve will rest on the solid bottom portion of the gate assembly and lie across the aperture and window. The gate is of such a size thatit is larger than the window opening in the X-ray tube but small enough in radius that it can be raised out of the path of X-rays emanating from the target on the anode of the X-ray tube.

The stainless steel bellows is soldered or welded to the face of the threaded cylindrical end 23 and the threaded end 23 is then secured to the coupling 19 by the threads thereon. When the gate assembly is secured to the coupling, the aperture 26 of the gate assembly is in axial alignment with the window 14 and the gate valve 27' is adapted to be moved across the window proximate thereto or stored in a position out of the path of any X-rays emanating from the X-ray tube.

The top portion 32 of the gate assembly housing through which the draw rod 31 passes is milled at and has a shallow hole`33 of larger diameter than the hole through which the draw rod passes. Any suitable gasket 34 is placed in theV shallow hole 33 to Yprovide a vacuum tight seal about the draw'rod. The vacuum seal gasket is held in place-by a plate 35 and screws 36 which screw into appropriately threaded holes 37 in the top at surface of the gate valve assembly. The draw rod can be moved by any desired method; however, it is shown as having a threaded end which passes through a knurled nut 38 which is held in place withinv a slot 4l of a slotted element 42 which is secured to the plate 35 that holds the vacuum seal in place. As the knurled nut is rotated the draw rod will be fed through the nut Ato either lower or raise the gate and the nut will be restrained by the slotted element.

For thepurpose of securing the X-ray tube-gate valve assembly to a vacuum system, the outer face of the solid end of the gate valve assem ly has a circular groove 43 therein for receiving'a gasket, not shown, and holes 44 in the outer portion through which bolts pass to secure the gate va1ve-X-ray`tube assembly to a matching surface in the vacuum system.

In assembling the X-ray tube-gate assembly into oneV unit, the X-ray tube is assembled by the usual process of securing the cathode, anode, window, etc., to make up the tube. The gate assembly can be assembled by many The gate valve is heldin place within the cylindrical structure, then the guide rods are passed through the holes therein and the cylindrical structure is secured in the housing by appropriate bolts. The draw rodY 3l is then passed through the hole in the rim and screwed into the threaded hole in the gate valve. The vacuum seal is positioned in place and then the vacuum seal plate is placed down over the draw rod and secured to the milled at portion of the rim. The knurled nut is held in position within the slot of the slotted element and screwed onto the draw rod until the slotted element reaches the vacuum seal hold down plate, then the slotted element is secured to the vacuum seal hold down plate. The gate valve assembly housing and X-ray tube are now separately assembled. The stainless steel bellows is secured to the X-ray tube base at one end and the coupling is slid over the bellows and screwed onto the threaded end of the X-ray tube. The other end of the bellows is then secured to the face of the gate valve assembly housing and the coupling is screwed onto the' be held in place against the guide bars by the force ap- I plied by the end of the X-ray tube on the gate valve.

Once the gate valve is secured in place in a vacuum tight seal by the sharp end of the X-ray tube about the thin window, the vacuum pressure within the area confined by the base of the X-ray tube, the gate valve and the stainless steel bellows will be about 10-5' mm. Hg. Also, the area conned by the sharp end of the X-ray tube between the gate valve and the Vthin window will have a vacuum pressure of l0d5 mm. Hg. This vacuum pressure will be maintained until the end of the X-ray tube is moved away from the gate valve. The knurled nut and slotted element, the vacuum seal hold downV plate, and the vacuum seal are removedfrom the gate valve assembly, then the X-ray tube-gate valve assembly is disconnected from the vacuum system. The X-ray tube will now have the same vacuum pressure on each side of the window due to the gate valve being in a vacuum tight seal with the end of the X-ray tube. The evacuation of the X-ray tube is continued and the tube is baked at a high temperature of about 250 C. to about 450 C., and pumped simultaneously until an ultra-high vacuum of about 10-g mm. Hg

moved from the baking oven, the vacuum seal and knurled nut, etc., is assembled back onto the gate valve assembly housing. The X-ray tube-gate valve assembly can now be secured to a vacuum system for operation wherein the vacuum system is pumped to l0-5 mm. Hg with the X-ray tube-gate assembly in place. Once 10-5 mm. Hg has been reached in the vacuum system, the gate valve can Vbe sure of about 10-9 mm. Hg within the tube envelope and a vacuum system which is operable at 10-5 mm. Hg.

Thus, there will be no harmful efects on the thin windowk during bakeout or operation and the X-ray tube can be removed from the vacuum system without any harmful effects on the thin window by properly securing the' gate valve relative to the X-ray tube window.

Such an operational system is beneficial wherein one may wish to use an X-ray tube that can be disassembled for some reason. In disassembling the X-ray tube, atmospheric pressure must be admitted intothe tubeY and vacuum system simultaneously at the same rate toprevent breakage of the thin window. Y

Thus, thedevice of this invention permits one vto use very, very thin windows which are useful in soft X-ray research and also provides a simple, convenient manner'forV making X-ray tubes with an ultra-high vacuum of about l0-9 mm. Hg. Thin windows referred to are of about to 100() angstroms, or l06 cm. to 10-5 cm. thickness.-

4 A1203 Windows as referredtto herein are well known in the art and are made by hot pressing aluminum onto a steel ring of a diameter just larger than the desired window opening in the X-ray tube envelope. The aluminum is oxidized to the desired thickness and then the aluminum is etched away by any well known process, leaving the oX- idized aluminum for the window. The steel ring affords a good material for securing the window to a metal envelope and the oxidized aluminum arlords a very, very thin window, as noted above.

Heretoiore, there was mentioned that the screw threads on the base of the X-ray tube are thirty-two threads to the inch and that the screw threads on the gate valve assembly housing are twenty-four threads per inch, each of which are right hand threads. The purpose for this arrangement is to advance the X-ray tube toward the gate valve at a very slow rate. As the coupling nut screws onto the cylindrical threaded portion drawing the gate valve toward the X-ray tube at a rate of twenty-four threads per inch, the coupling is simultaneously moving the X-ray tube away from the gate valve at a rate of thirty-two threads per inch. Thus, the advance of the X-ray tube toward the gate valve is very slow, approximately 0.01042 inch per revolution. rEhe slow advance of the gate valve toward the X-ray tube insures a good seat which is irnportant in making a good vacuum seal between the end of the X-ray tube and the gate valve. The gate valve is assembled proximate the sharp surface of the X-ray tube and therefore requires only a very short linear movement between the two surfaces to make a vacuum tight seal or to separate the end of the X-ray tube from the gate valve for operation of the tube Jor X-ray production.

As noted above, the gate valve housing and gate valve assembly are made separately. This provides for better engineering and since the gate valve moves along guide rods, these guide rod openings are on the inside of the housing and do not need any vacuum seals. t these guide rods extended through the housing, seals would be re quired. Since the only element that passes from the outside of the housing to the inside is the gate valve draw bar, there is a requirement for only one outside vacuum seal. lt is also noted that the vacuum seal can be removed without breaking the vacuum of the X-ray tube,

during balteout or during the time the X-ray tube is not assembled into a vacuum system by use of the gate valve.

Obviously many modcations and variations of the present invention are possible in the light of the above teachings. it is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specically described.

What is claimed is:

1. In combination an X-ray tube envelope including a window and a gate valve movable relative to said window, said gate valve being secured proximate said window perpendicular to an axis through said envelope and said window, means for moving said gate valve relative to said Window into separate positions across said window and out of line with said window, and means associated with said envelope and gate valve to move said envelope and gate valve linearly along the axis relative to each other such that the window end of said X-ray tube envelope is in a vacuum tight seal with said gate valve when moved to malte physical contact with each other and to linearly separate said X-ray tube envelope from said gate valve.

2. A gate valve for protecting the window of a highly evacuated X-ray tube when in a surrounding of atrnospheric pressure which comprises a gate valve housing adapted to be positioned adjacent to said X-ray tube window to be protected and in axial alignment therewith, a gate valve in said housing adapted to be guided from a position above said X-ray tube across said window perpendicular to the aYs and parallel with said window 1n proximity thereto, and a drive means for forcing said X-ray tube and said gate valve housing axially toward each other such that the window end of said X-ray tube may contact said gate valve to provide a vacuum seal therebetween and to move said X-ray tube and said gate valve housing away from each other such that said gate valve may be moved from a position across said X-ray tube window.

3. ln combination, an X-ray tube and a gate valve housing and gate valve assembly positioned relative to each other with axial movement relative to each other, said X-ray tube including a base, an envelope secured to said base, a thin window is axial alignrnent in said envelope with an envelope extension about said window and a cathode and anode positioned relative to each other within said envelope adjacent to said window, said gate valve housing and gate valve assembly including a cylindrical housing, a front wall, an axial aperture in said front Wall, said gate valve assembly being secured in said gate valve housing, said gate valve assembly including a gate valve movable within said housing paralle with said front wall and said window in said X-ray tube perpendicular to the axis of said tube and said housing, said gate valve being positioned proximate said window and adapted to be held in a position out of aiignrnent with said window and said aperture and also to be positioned across said Window, means for moving said X-ray tube and said gate valve housing in directions toward each other and in directions away from each, said X-ray envelope extension about said window adapted to engage said gate valve when in a position across said window to prevent pressures outside of said X-ray tube from aecting said window, and a bellows surrounding said X-ray tube envelope and connected to said X-ray tube base and to said gate valve housing.

References Cited in the le of this patent UNlTED STATES PATENTS 2,292,087 Ramo Aug. 4, 1942 2,340,362 Atlee et al. Feb. 1, 1944 2,375,223 Hansen et al May 8, 1945 2,522,062 Roovers Sept. 12, 1950 2,637,818 Gund et al. May 5, 1953 2,665,391 Bleeksma Jan. 5, 1954 2,749,203 Hardwick lune 5, 1956 FOREIGN PATENTS 183,721 Switzerland Apr. 30, 1936

Claims

1. IN COMBINATION AN X-RAY TUBE ENVELOPE INCLUDING A WINDOW AND A GATE VALVE MOVABLE RELATIVE TO SAID WINDOW, SAID GATE VALVE BEING SECURED PROXIMATE SAID WINDOW PERPENDICULAR TO AN AXIS THROUGH SAID ENVELOPE AND SAID WINDOW, MEANS FOR MOVING SAID GATE VALVE RELATIVE TO SAID WINDOW INTO SEPARATE POSITIONS ACROSS SAID WINDOW AND OUT OF LINE WITH SAID WINDOW, AND MEANS ASSOCIATED WITH SAID ENVELOPE AND GATE VALVE TO MOVE SAID ENVELOPE AND GATE VALVE LINEARLY ALONG THE AXIS RELATIVE TO EACH OTHER SUCH THAT THE WINDOW END OF SAID X-RAY TUBE ENVELOPE IS IN A VACUUM TIGHT SEAL WITH SAID GATE VALVE WHEN MOVED TO MAKE PHYSICAL CONTACT WITH EACH OTHER AND TO LINEARLY SEPARATE SAID X-RAY TUBE ENVELOPE FROM SAID GATE VALVE.