US2791708A - X-ray tube - Google Patents

Description

y 7, 1957 J. T. SERDUKE 2,791,708

x-RAy TUBE Filed Feb. 6. 1955 IN MENTOR z/lwcs T SCROU/(fi United States Patent X-RAY TUBE James T. Serduke, El Cerrito, Calif.

Application February 6, 1953, Serial No. 335,610

2 Claims. (Cl. 313-55) (Granted under Title 35, U. S. Code (1952), sec. 266) This invention 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.

The invention relates to X-ray or gamma ray tubes and, in particular to tubes capable of developing high intensity rays.

As is well known, X-rays have many valuable uses, both in industry and in scientific research, and in av number of these uses it is both desirable and possible to vary or control the type of ray produced so as to render it most suitable for the particular job to be performed. For example, in various types of medical treatments, it is desirable to produce what is known as soft ray, while in other operations, such as industrial metallurgy, a high intensity hard ray is far more effective. Of course, much effort has been expended in the production and control of both general types of rays and these efforts have for the most part met with considerable success.

However, one major difiiculty has been experienced in the production of unusually high intensity rays and this difiiculty may be traced directly to the fact that such metals as are available for the X-ray targets or anticathodes are incapable of withstanding the tremendous heat generated upon their bombardment by the electrons of the cathode stream. It has been, of course, manifest to all that more effective means for dissipating or absorbing this heat would have to be developed, but even though some advances were made, the prior art apparently has been unable to efiectively dissipate the intense heat produced by currents of a magnitude required for the production of maximum intensities. In fact, the heat dissipation problem has not, so far as is presently known, been solved for currents in the neighborhood of milliamperes and power supplies around 50,000 volts for over one minute of exposure time. Compared to this, it might be noted that some operations employ currents in the neighborhood of 400 ma. For example, such currents are needed to produce the intensities desired for use in such increasingly important fields as the calibration of radioactive measuring instruments, as well as in research projects involving the biological orphysical study of specimens that have been subjected to radioactive dosages.

As has already been indicated, X-rays of such high intensities have not been made avail-able due to the fact that no suitable means has been provided for dissipating or carrying off the heat generated, and, further, no target material has been found that is capable of withstanding the heat to which it would be subjected. Such attempts as have been made principally were directed. along the line of utilizing a rotating target, the surfaces of which would be successively exposed to the cathode stream bombardment as the target is rotated and then immediately cooled by a passage through a coolant which normally was carried outside of the vacuumized area of the tube. However, one rather obvious difiiculty involved in such rotary, cooled targets is that some sealing means has to be provided to permit the target to pass through 2 the vacuum tube wall and into the coolant, and the provision of such a seal has proven an almost insurmountable barrier. In other types of rotary tubes, the target was mounted on a relatively large mass of conductive metal. In such tubes, no seal was required because the heat dissipating metal all was contained in the vacuum area of the tube, but, even so, there arose an attendant diiliculty in that the target and its supporting mass had to be mounted in a bearing and, as would be expected, it proved close to impossible to provide a suitable lubricant for a bearing surface that is disposed in a vacuum. Other attempts at dissipating the high heat caused by the cathode stream bombardment were directed along diiferent lines, but so far as is presently known, none of these attempts were successful in producing a tube capable of utilizing a maximum available voltage in a manner that would produce a maximum high intensity ray.

One of the objects of the present invention is, therefore, to provide an X-ray tube that is capable of producing rays of unusually high intensity or, viewed in another manner, a tube that is capable of withstanding the high currents and sustained voltage necessary to produce such high intensity rays.

A correlative object is to provide a means for dissipating extreme heat generated at the targets of X-ray tubes or, more specifically, to provide a means for effectively cooling targets subjected to currents of a magnitude of 400 or more milli-amperes.

A further object, which will be clarified by the ensuing description, is to provide an X-ray tube in which the ray emanations are capable of being concentrated upon a small object in such a manner as to utilize the maximum cumulative ray intensity.

Yet another important object is to provide a simple, effective and entirely practicable means for increasing the presently available X-ray tube ray intensity.

According to the present invention, such objects are achieved fundamentally by increasing the surface area of the anti-cathode or target and, further, by permitting the cathode stream to evenly distribute itself over the entire target surface area. Along with this arrangement, there also is provided a target cooling means that is capable of dissipating the heat evenly from the entire target surface area. As can be surmised, the net result of the arrangement is that the heat, which previously was concentrated on a small target surface area is, according to the present invention, distributed over a large surface area, each portion of which can be subjected to at least the same cooling action as was available for the small targets.

Preferably, -a circular target is employed and the cathode is disposed centrally or concentrically within it. Further, the target itself is mounted on a cooling jacket which, most suitably, is formed of a conductive metal and is provided with an inlet and outlet for a coolant such as water, Freon under pressure or liquid nitrogen under pressure.

As would be expected, the electron stream emanating from the cathode is projected in uninterrupted radial directions onto the concentrically spaced target which, when so bombarded, radiates an X-ray beam toward its objec tive. Further, although the electron stream, preferably, is unconfined in its radial ditfiusion, it is desirable to confine or limit its beamed width so as to assure that the major portions of its electrons strike the target. This may be accomplished quite simply by utilizing a ray-pro ducing ring and mounting this ring in a recess which has lips or a mouth of suitable constriction to project a beam of such a width that it covers, but does not spread beyond, the limited surface area width of the target.

Another important feature of this invention is that the target ring may be disposed at such a conical angle that the cathode stream rays emanating from the entire circular surface area, converge toward a central concentration area in which the object to be studied may be placed. This latter feature of concentrating or focusing the produced X-rays is most desirable when the tube is used to study small objects because, in such an event, the cumulative intensity of the major portion of the rays can be brought to bear on this object. Of course, such a focused or narrow-beam ray is desirable only in certain work, and, where a broad beam would be more effective, the disposition and mounting of the target can be varied.

The preferred embodiment of the invention is illustrated in the accompanying drawings of which Fig. l is a partially broken longitudinal section through the target end of an elongate X-ray tube, and Fig. 2 a transverse horizontal section along lines II-JI of Fig. 1.

Referring to the drawing, the tube illustrated has most of the conventional elements normally employed inX-ray tubes, although, of course, these elements are specially designed and arranged to accomplish the purposes of the invention. Thus, the tube is formed of the usual glass body wall 1, the lower portion of which is not shown because it may be formed in any conventional manner with suitable tines for coupling the tube into a power supply, as well as other well-known elements. Further, as might be anticipated, this tube is of a general type adapted to be heated by an external electric circuit and, in view of this, cathode 2, which extends axially of the elongate tube, is provided at its upper end with an enlarged head portion 3 in which is mounted a spiral heater filament 4. Filament 4, as may be noted in Fig. 2, is circular in shape and it is used to indirectly provide heat for a cathode stream emitting ring 6 dis-posed concentrically about filament 4 in axial alignment with both the filamerit and longitudinal axis of the cathode. Ring 6 may be formed of any suitable material, such, for instance, as lanthanum boride, which has been found most efieetive for the present purposes. Also, for reasons to be explained, this cathode stream emitting ring is mounted in a recess 7 formed on the periphery of head 3 and, as would be expected, the cathode stream emanating from the ring is capable of proceeding outwardly in an uninterrupted fashion throughout a 360 degree angle.

The remaining functional elements of the tube include a cooling jackets secured to the upper edges of body wall 1, an anti-cathode or target 9 and a hemispheric globe or cap 11, both of these latter elements being mounted on cooling jacket 8. Preferably, jacket 8 is coupled to glass wall 1 by means of a special ring member 12 formed of a metal that is capable of expanding and. contracting with the glass. Also, hemispheric cap 11 may be formed of a similar metal, and one such metal that is particularly suitable is that commonly referred to as Kovar.

As has been indicated, one of the important features of this invention is that the surface area of target 9 is enlarged to such an extent that it can be effectively cooled regardless of the electron bombardment to which it is subjected and the preferred manner in which this is accomplished can readily be appreciated in the drawings. Thus, as may be noted in Fig. 1, target 9 is formed of a circular metal plate, which may be gold or other suitable metal, and the plate is mounted in flush engagement with an inner wall 13 of cooling jacket 8, this inner wall being spaced concentrically from ring 6. Accordingly, the surface area of the target is enlarged to as great an extent as possible and, as would be expected, when the target is properly positioned on jacket 8, it is capable of intercepting the entire 360 degree projection of the electron stream issuing from cathode ring 6. In other words, both the electron stream and the target are expanded to as great a degree as possible with the obvious result that each surface portion of the target is bombarded by a minimum number of electrons. It, of course, follows that each such target portion will be heated to a correspondingly lesser degree than would be the case if the entire electron stream were concentrated on one small area. Such acondition is most desirable, because, with the bombardment so dispersed or distributed over the wide area, it is possible to effectively dissipate the heat from the target by providing means, such as jacket 8, to cool or evenly dissipate heat from the entire surface of the target. The increased heat dissipation results because the cooling at any particular spot on the target is at least as great as previously was available, while the heat generated at that spot is substantially less due to the distribution of the electron stream over a wide area.

Most suitably, jacket 8 is formed of a U-sh'aped copper plate, its interior chamber being closed by a suitable rass or copper ring 13 that may be soft soldered to the upper and lower legs of the U. Also, plate 13 is adapted to mount a plurality of coolant inlet and outlet pipes 14 and 1.6, while interiorly of the jacket is mounted a baffle plate 17 disposed to direct and regulate the flow of the coolant. As has been stated, the coolant may be water, although, where more extreme conditions are to be met, it may be Freon under pressure, liquid nitrogen under pressure, or other well-known fluids 'or materials.

It also, as might be expected, is desirable to assure that all of the electrons emanating from cathode ring 6 strike target 9 and do not spreadout beyond the width of the target so as to ineffectively bombard surrounding surfaces of the jacket or tube cap. Such assurance presently is achieved by mounting ring-6 in recess 7 which, as previously stated, is formedwith a mouth portion suitably constricted to narrow the issuing beam to such a width that it will just cover the target width. The shaping of the recess mouth will, of course, depend upon the size and spacing of the target, and such details will have to be worked-out for each different tube Yet another important feature of the invention is that the X-ray beams which emanate from the 360 degree tar get source, are projected toward a focus so as to permit substantially all of the rays produced to be concentrated on such small objects as are to be studied or tested. This particular featureis accomplished by'mounting target 19 at a suitable angle much in the same manner as the retlectors of a search light are mounted to focus the search light beam. However, it is appreciated that such a narrow focused beam is not desirable in some operations, and, if such'an operation is presented, target 9 can be disposed at any angle desired. However, in any rearrangement or modification of the illustrated structure, it should be borne in mind thatbecause of high voltage any sharp corners should be avoided and, in fact, it is for this reason that jacket 9 is provided at its bot-torn inner end with a rounded shield 18.

In the foregoing description, the emphasis primarily has been upon the provision of a circular target or anticathode disposed concentrically about a central cathode. However, as will be appreciated, the advantages obtained by the invention can be achieved, at least to a limited ex- .tent, by the use of targets shaped in other manners. Thus, if desired, a plurality of spaced-apart targets which, in total, form a ring, or a substantial portion of a ring,

could be utilized. Also, it conceivably might be desired to use a smaller semi-circular target and, to the extent that such a target would accomplish the purposes of this invention, it also is considered within the intended scope.

As has been stated, the tube provided is particularly beneficial for use Where unusually high X-ray intensities are desired or required. Thus, the target of the present tube is effectively cooled even under such electron bombardments as would be produced with sustained power supplies of 250 to 500'kv. and with currents in the neighborhood of 400 ma. However, the teachings of the invention may very well be useful in tubes which are not required to meet such high intensity conditions, so that there is no intent to limit the scope of the invention to high intensity applications. In fact, many applications of the present teachings might be anticipated because, regardless of the X-ray intensity produced, the structure of the tube provided is unusually simple and efiective and,

compared particularly with the difficulties experienced with the rotary-type targets, the present tube is unusuallypractical and uncomplicated.

Obviously, many modifications 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 specifically described.

I claim:

1. An X-ray tube comprising a stationary cathode formed with a continuous circumferential recess, a cathode ray-ernitting ring continuously mounted in said recess, a stationary circular disc-shaped target disposed radially-outwardly of and concentrically about said rayemitting ring, and a fluid-circulating coolant jacket, said recess being shaped to direct rays radially onto the full surface area of said target and said target being formed as a truncated cone obliquely diverging from said radial ray paths, said jacket being formed withv a thin-walled portion facing said ring and contiguously engaging and supporting a face of said target.

2. An X-ray tube comprising a stationary cathode formed with a continuous circumferential recess, a cathode ray-emitting ring continuously mounted in said recess, a stationary circular disc-shaped target disposed radiallyoutwardly of and concentrically about said ray-emitting ring, and a fluid-circulating coolant jacket shaped to pro vide an elongate interior chamber, said recess being shaped to direct rays radially onto the full surface area of said target and said target being formed as a truncated cone obliquely diverging from said radial ray paths,

said jacket including a circular thin-walled portion facing said ring and disposed in contiguous supporting engagement with a face of said target, a partition wall longitudinally dividing said chamber into inlet and outlet passages, and a plurality of radially-spaced inlet and outlet coolant ports for increasing the circulation rate through said chamber.

References Cited in the file of this patent UNITED STATES PATENTS

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