US2292859A

US2292859A - X-ray tube

Info

Publication number: US2292859A
Application number: US376633A
Authority: US
Inventors: Allibone Thomas Edward
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1939-11-02
Filing date: 1941-01-30
Publication date: 1942-08-11
Anticipated expiration: 1959-08-11
Also published as: GB536941A; BE468984A; FR930261A

Description

T. E. ALLIBONE X-RAY TUBE Filed Jan. 30, 1941 2 Sheets-Sheet l.

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of New York Qompany, a corporation Application January 30, 1941, Serial No. 376,633 In- Great Britain November 2, 1939 7 Claims,

This invention relates to X-ray tubes and concerns target or anti-cathode arrangements therefor.

In many X-ray tubes for-X-ray therapy the X- rays utilised for treatment are those which leave thefront surface of the target or anti-cathode, that is to say the surface thereof on which the cathode ray beam impinges. In a relatively few tubes, on the other hand, and especially in X-ray 7 tubes operatingat very high voltages, these tubes being necessarily the reverse of portable and often completely immobile and bulky, a transmission type of target has been incorporated. Such a target is comparatively thin so that as its name implies X-rays' generated near its front surface can be utilised after being transmitted through the target. Thus, with a transmission target it is possible to utilise for X-ray treatment two separate beams, the one from the front surface of the target, and the other from the reverse surface thereof in the direction of the cathode ray beam. Such two beams may be directed at any angle to each other, in practice usually at rightangles to each other. Thus for treatment purposes relatively immobile tubes of the kind above indicated possess some flexibility in relation to the setting up of a patient with respect to the direction of the X-ray beam.

Now it has been found that th character of the X-ray beams in the two directions mentioned in the preceding paragraph is different. The difference increases with increasing voltage on the X-ray tube. The difference, moreover, is only of important magnitude for X-ray tubes operating on really high voltages, for example above half a million volts. The transmitted beam emerging' in the direction of the cathode ray beam is of greater intensity and has greater penetrating power than is the case with the beam emerging in almost any other direction.

The-present invention on the one hand makes available such increased intensity and penetrating power, and on the other hand enables the transmitted beam to be caused to emerge atydifferent angles with respect to the-cathodebeam' in tubes which will normally be bulky; heavy and substantially immobile, so that the same degree mission target or anti-cathode together with means by which the cathode ray beam, in the neighbourhood .of the target, can be deflected from its normal direction to at least one other direction, the target moreover being curved or shaped so that the cathode rays in the non-deflected and the deflected positions fall approximately at right-angles upon the front surface of the target. There is preferablyassociated with the aforesaid target, which is formed of a metal of high' atomic number or is plated on its front face withisuch a metal; a shield such as of lead orother 'X -ray absorbent material, which shield has an opening within which is the evacuated tube through. which passes'the undeflected portion; of the cathode ray beam on its way. from the cathode to the target. Said shield moreover has a plurality of apertures through which the transmitted'X-rays can emerge in accordance with the condition. of the deflection of the cathode ray beam. Or,'alternatively, there may be a single aperture for the emerging X-ray beam Whilst the shield is rotatable.

Means for variably deflecting the cathode ray beam may comprise a magnetic winding which may-behoused within a cavity in the aforesaid shield"; in close proximity to that end of the evacuated envelope'at which is disposed the aforesaid curved transmission type target or. anticathode.

In carrying out the invention according to one arrangement thereof .the target may consist of sheet metal bent to cylindrical or approximately cylindrical form and having its open ends closed by discsv of metal. There is thus provided an evacuated drum-shaped chamber from which there extends radially the evacuated tube through which pass into the chamber the undeflected cathode rays from the X-ray tube cathode.

.The aforesaid cylindrical transmission target isupreferably surrounded by another cylindrical member with flanges so as to form around the target a jacket through which cooling fluid can pass; 'Ihe flat discs or side faces of the drumshaped' chamber may be similarly jacketed for cooling purposes. The deflecting coil may comprisetwo parts one on each side of the drumshaped chamber, and if desired iron may be associated'with such two parts of the solenoid to assist inproducing the field strength requisite for deflection.

The surrounding X-ray shield member may also be in the form of a'drum-shaped member having the internal cavity and also the apertures as aforesaid. Saidshield conveniently consists of a Welded steel chamber filled with lead or lead shot ticularly with respect to the aforesaid evacuated tube through which the undeflected cathode rays pass towards the anti-cathode chamber or drum. In such case there is preferably a single radial aperture in the shield for the emerging X-rays so that by deflecting the cathode ray beam by various amounts and by rotating the shield said aperture can be brought into alignment with the transmitted X-ray beam wherever it may be caused to impinge on the inner face of the cylindrical target or anti-cathode.

There may be optionally provided a tube having a closed end, fixed radially with its open end communicating with the drum-shaped chamber, at an angle, conveniently of 90 to the aforesaid tube through which the undeflected rays pass to the drum-shaped chamber. Such arrangement provides a useful means of disposing of the cathode ray beam when the X-rays are not required since said additional tube attachment may have the cathode rays deflected into it and may be made of metal having a relatively low atomic weight and may be relatively conveniently surrounded by sufficient lead or other X-ray shielding material. This tube should be fluid-jacketed and long enough to allow the desired thickness of shielding lead or the like to be placed around it. With this arrangement, moreover, it will be appreciated that the X-ray beam may be utilised for treatment over an angle of, say, 120 or even as much as 180".

It will be appreciated however that the arrangement described above involving the drumshaped chamber allows of the X-rays being deflected in one plane only. This is in general suflicient since other degrees of flexibility for treatment can be obtained by reason of adjustability incorporated in the couch on which the patient is placed. However, greater flexibility of the angle of X-ray beam emergence may be obtained by making the anti-cathode wholly or in part spherical and surrounded by a spherical fluid-cooling jacket having means for ensuring rapid and even flow of the cooling fluid over the whole chamber such as by providing guiding baffles and/or a plurality of inlet and outlet ports for the cooling fluid. Deflection of the beam may be, as previously, by means of a solenoid which, again, is mounted in the shield, which in this case may be externally substantially cubical, said shield being so mounted that it may be rotated as desired through two axes which are at right-angles to each other and pass through the centre of the spherical evacuated anti-cathode chamber. In this arrangement the shield may be provided with a single conical aperture for emergence of the X-ray beam. Then, it will be appreciated, the emergent X-ray beam may, within limits, be directed to any desired angle by merely moving the universally mounted shield which has the deflecting solenoid fixed in the cavity therein.

In general the amount of deflection depends both on the strength of the magnetic deflecting field and on the voltage applied to the X-ray tube. If this voltage is constant the beam will be homogeneous and the deflected spot will be a little larger than the undeflected spot. If, however, the voltage is not constant the beam will be spread out into a velocity spectrum, and it will then be possible by rotation of the surrounding lead shield to select the X-rays from the region of the least deflected cathode rays. Thus the selected X-ray beam will be more penetrating than would be the beam from the undeflected cathode rays, and such may be advantageous.

In the accompanying drawings diagrammatically illustrating the invention by way of two examples,

Figure 1 is a sectional elevation of one form of the invention, and

Figure 2 is a sectional elevation of that form taken at right angles, the target being of drum shape.

Figure 3 is a view similar to Fig. 2 showing a modification wherein the target is spherical.

Fig. 4 is an elaboration of Fig. 3 showing certain details of structure which are omitted in Fig. 3.

Referring to Figs. 1 and 2, at I is shown the cylindrical target closed by end discs 2 and sursounded by the cooling jacket 3 having parts 4 and 5 whilst at 6 is shown the tube down which the cathode rays pass into the drum I, 2. The shield member surrounding the latter is shown at I. This has the X-ray port 8 and the slot 9 to permit the shield member being rotated about the axis of the drum-shaped chamber I, 2. Within the cavity of the shield member I are shown in Fig. 2 the two portions of the deflecting solenoid I0. At II (Fig. 1) is shown the optionally provided tube into which the cathode ray beam may be deflected when, though the X-ray tube may be still excited, the X-rays are temporarily not required. The curved lines I2 (Fig. 1) are indicative of how the cathode ray beam I3 may be varyingly deflected within the drum I, 2 by appropriate excitation of the solenoid I0.

The arrangement illustrated by Fig. 3 only differs from that illustrated by Figs. 1 and 2 in that the target I a. and its cooling jacket 30. are spherical, whilst the shield member la is cubical, with a cubical cavity within which latter are the two parts of the solenoid I0.

It is apparent that the combination of the shield Ia and the enclosed target structure forms the equivalent of a ball and socket arrangement adapted to permit rotary motion of the shield about mutually perpendicular axes. The limits of such motion are set, of course, by the size of the shield opening 8a, and it may be desirable in some cases to make this opening considerably larger than in the arrangement illustrated.

The possibility of rotation of the shielding structure about mutually perpendicular axes is further illustrated-by Fig. 4 which is in efiect an elaboration of Fig. 3. In this case the cooling jacket I3 which surrounds the spherical target II is in contact with conventional friction reducing means (e. g. ball bearings I4) which also bear upon a cooperatively positioned part I5 of the shielding structure I6. Handles I! mounted on the shielding structure make it possible for an operator grasping the handles to rotate the shielding structure and the enclosed deflecting coils I9 about the target. Rotation about an axis B, assumed perpendicular to the drawing, may obviously beaccomplished by downward pressure on either of the handles I1, I1. Rotation about the axis AA (perpendicular to B) may be produced, on the other hand, by pulling or pushing on both handles concurrently.

It will be understood that the two arrangements specifically described are given by way of example only since the curved anti-cathode may assume various forms for example, in accordance with the characteristics of the particular deflecting means employed.

I claim:

1. In combination, an X-ray tube having a stationary cathode adapted to serve as the source of a cathode ray beam, a stationary target with at least two materially displaced areas capable of generating X-rays under the impact of the said cathode ray beam, and means for deflecting the said cathode ray beam relative to the target to cause it to be fixed alternatively upon one or the other of the said areas, whereby X-radiations may be projected from the tube in different directions depending upon the particular one of said target areas at which said radiations are generated.

2. In combination, an X-ray tube having a stationary cathode adapted to serve as the source of a cathode ray beam, a stationary target with at least two materially displaced areas capable of generating X-rays under the impact of the said cathode ray beam, shielding means associated with said target for'channelizing in different directions X-rays generated at the various ones of said areas, and means for deflecting the said cathode ray beam relative to the target to cause it to be fixed at the will of an operator upon a selected one of the said areas.

3. In combination, an X-ray tube having a stationary cathode adapted to serve as the source of a cathode ray beam, a stationary target with a surface which is of concave curvilinear contour and which is capable over at least a substantial portion of its area of generating X-rays under the impact of the said cathode ray beam, and beam-deflecting means operable at the will of an operator to fix the said cathode ray beam on various selected parts of the said surface, whereby X-radiations may be projected from the tube in different directions.

4. In combination, an X-ray tube having a transmission target of extended surface area which is capable over at least a substantial portion of its area of generating X-rays under the impact of a cathode ray beam, adjustable shielding means externally enclosing the said target for confining the projection of X-rays from the tube to a single direction controlled by the orientation of the shielding means, and beam-deflecting means adjustable at the will of an operator to fix the cathode ray beam of the tube upon various selected parts of the target surface, whereby through correlated adjustment of the said beam-deflecting and shielding means X-rays may be projected from the tube in any one of a plurality of difierent directions.

5. In combination, an X-ray tube having a stationary cathode adapted to serve as the source of a cathode ray beam, a stationary target of extended surface area which is capable over at least a substantial portion of its area of generating X-rays under the impact of the said cathode ray beam, a magnet coil in proximity to the target and controllable at the will of an operator to fix the said cathode ray beam on any one of a number of different areas of the target surface, and shielding means for channelizing the X-rays generated at any of the said different areas.

6. In combination, an X-ray tube having a hollow, generally spherical transmission target, shielding means surrounding the target and having an X-ray pervious portion for facilitating the egress of X-rays through the shielding means, the said shielding means having at least two axes of possible rotation which are at right angles to each other and which pass through the center of the target whereby the said X-ray pervious portion may be brought into proximity to various selected areas of thetarget, and beam-deflecting means controllable by an operator for fixing the cathode ray beam of the tube on various areas of the target corresponding to areas which may be subtended by the said portion of the shielding means.

7. In combination, an X-ray tube having a hollow transmission target, shielding means surrounding the said target and having an X-ray pervious portion for facilitating the egress of X-rays through the shielding means in a single direction, the shielding means being adjustable to vary the location of the said X-ray pervious portion, and a magnet coil in proximity to the said target for variably deflecting the cathode .ray beam of the tube over the surface of the said target in dependence on the orientation of the coil, the coil being movable with the said shielding means, whereby through concurrent adjustment of the coil and of the shielding means the region of generation and the direction of egress of X-rays from the said tube may be simultaneously controlled.

THOMAS EDWARD ALLIBONE.

I CERTIFICATE OF CORRECTION. 1 Patent No. 2,292,8 9. August 11, 19 L|.2.

THOMAS EDWARD ALLIBONE.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 5, first 'column, line 24., claim 1, for "said radiations" read -such radiationsline L .O, claim 5, after "stationary" insert "transmission"; and that the said Letters Patent-shouldbe read with thiscorrection therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 22nd day of September, A. D. 1914.2.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents.