US2053327A

US2053327A - X-ray tube

Info

Publication number: US2053327A
Application number: US754231A
Authority: US
Inventors: Louis F Ehrke
Original assignee: Westinghouse Lamp Co
Current assignee: Westinghouse Lamp Co
Priority date: 1934-11-22
Filing date: 1934-11-22
Publication date: 1936-09-08
Anticipated expiration: 1953-09-08

Description

56 5'; s, 1936. L. F. EHRKE v 4 2,053,327

I X-RAY TUBE Filed Nov. 22, 1934 INVENTOR A [HP/ff ATTORN EY Patented Sept. 8, 1936 UNITED STATES PATENT orrlca X-RAY TUBE Pennsylvania Application November 22, 1934, Serial No. 754,231

Claims.

My invention relates to X-ray devices and comprises in particular a new X-ray anode or target which is particularly adapted for use in connection with the continuous generation of X-rays,

5 for example, in the administration of therapeutic treatments.

In the usual construction of such X-ray tubes it is customary to provide a surface of a refractory metal, such as tungsten or the like, molecularly secured to a stem of good heat conducting metal, such as copper. During operation of the tube the electron stream flowing from the thermionic cathode is more or less concentrated upon the refractory metal surface resulting in the generation of X-rays as well as considerable heat which is transmitted to the anode stem. The high potential electrical energy for the tube is usually supplied from a high tension sourceand either rectified by the X-ray tube itself or by intermittent direct current by the utilization of a separate rectifier. Accordingly the anode surface or target is subjected to severe mechanical shocks caused by the'intermittent bombardment thereof accompanied by periods of intense heating followed by intervals of cooling which has a tendency to cause cracking or tearing of the refractory metal target. as well as a buckling away from the back plate or anode stem.

It is accordingly customary to obviate undue heatingof; the anode in X-ray tubes, when employedfor therapeutic treatments or other conditions requiring a heavy load, to circulate a cooling and insulatingmaterial through the hollow anode stem in an endeavor to maintain an even temperature.

If water is employed the device cannot be advantageously rendered shockproof because of the high voltages-to which the tube is subject-ed and the fact that water is not dependable as a dielectric medium and may thustransmit the high electrical potential applied to the anode to other portions of the apparatus with resulting shocks to a patient or operator.

As a consequence it is expedient to utilize a high'dielectric fluid, such as hydrocarbon oils, but such fluids also have a disadvantageous feature in that after continued use of the tube its cooling .efliciency is considerably decreased. The apparent reason for this decreased eficiency resides in a cracking of the oil and the accumulation of a carbonaceous deposit on the interior surface of the hollow anode, particularly at the points of greatest heat concentration. This cracking of the oil may to some extent be promoted by the copper per se or any copper oxide which may be contained on the'interior surface of the anode and the carbonaceous deposit thus formed, because it has a low heat conductivity characteristic, acts after a short time as a heat insulator between the anode stem and the cool ing and insulating material.

It is accordingly an object of my present invention to provide an X-ray tube suitable for continuous operation wherein an anode is provided. through which a cooling and insulating material, such as oil circulates and the possibility of a carbonaceous deposit being formed thereon resulting in a decrease in the efficiency of the heat transfer is obviated.

Another object of my present invention is the provision of an X-ray tube having an anode which becomes heated'during operation of the tube'and wherein a cooling and insulating me-- dium is caused to circulate therethrough with the interior surface of the hollow anode being so constructed that any carbonaceous products which deposit thereon due to decomposition of the cooling and insulating medium will not be tenaciously held thereby.

A further object of my present invention is the provision of an X-ray tube having an anode which becomes heated duringoperation of the tube and wherein a cooling and insulating material is arranged to circulate through the hollow anode stem for the purpose of transmitting the heat from the points of greatest heat concentration to the cooling and insulating medium and the hollow anode stem is provided with a coating of a material difierent'from that of the anode stem which has an inappreciable afiinity for any carbonaceous deposits that may be formed due to cracking of the cooling and insulating material upon successive subjection to high temperature thus enabling a free circulation of the medium ov-era long period of time.

Still further objects of my present invention become obvious to those skilled in the art by reference to the accompanying drawing wherein,

Figure 1 is a side view of an X-ray tube constructed in accordance with my present invention. I

Fig. 2 is a sectional view on an enlarged scale of the anode construction of the tube shown in Fig. 1 with a portion thereof broken away, and

Fig. 3 is a sectional view in elevation also on an enlarged scale and taken on the line IIIIII of Fig. 1.

Referring now to the drawing in detail I have shown in Fig. l a substantially cylindrical evacuated envelope 5 which may be of uniform diameter or have a portion thereof in the vicinity of the cathode electrode of slightly less diameter for the conservation of space in actual use of the tube. The envelope is provided at one end thereof with a reentrant sleeve portion 6 to which is sealed in a manner well known to the art a cathode electrode shown generally at I. This electrode is provided with .a metallic focusing cup .8 having recessed thereina filamentary cathode 9 in accordance with the usual construction. The thermionic cathode 9 is arranged to receive heating current from a suitable source of supply through a pair of conductors II] and I2 as well as being connected to one side of a high voltage source of supply (not shown).

The opposite end of the envelope 5 is similarly provided with a reentrant sleeve portion I3 to which is appropriately sealed, such as by a feather edge copper annulus I4 (Fig. 2), an anode .electrode I5 provided with a refractory metal target I6, of tungsten, thorium .or the like, and having a recess I'I extending longitudinally thereof which terminates at the head of the anode immediately in back of the target IS. The anode I5 may be supplied with a potential from the high Voltage source of supply by means of a conductor 18 and the same may be cooled during operation of the tube by the circulation of a cooling medium interiorly of the hollow anode I 5 by the provision of concentric insulated conduits I9 and 20. Upon incandescence of the thermionic cathode 9 and the application of a high potential between the electrodes I and I5 electrons will flow from the thermionic cathode 9 and bombard the target It with the accompanying generation of X-rays.

In order to prevent any scattered or secondary electrons from the anode from impinging upon the glass walls of the envelope a sleeve 22 maybe provided which forms an integral part of the envelope by being sealed thereto at a point well behind the seal of the anode to the reentrant sleeve I3. This sleeve and its operation form no part per se of my present invention, but is shown and described more in detail in the copending application of C. M. Slack, Serial No. 750,633 filed October 30, 1934 and assigned to the same assignee as the present invention. In view thereof further description herein is deemed unnecessary.

The hollow anode I5 is adapted to be threadedly engaged by the outer insulated conduit I9 and the inner concentric conduit 20 extends longitudinally of the hollow anode well within the same to a point adjacent the rear surface immediately in back of the refractory metal target I6. During operation of the tube the cooling and insulating medium, such as a hydrocarbon oil, is arranged to circulate from a suitable reservoir (not shown) and enters the hollow anode I5 through the inner concentric conduit 20, where it discharges into the latter at the point of greatest heat concentration, namely, at the surface thereof immediately in back of the refractory metal target I6. After contacting the heated surfaces of the anode stem it flows through the outer concentric conduit I9 back to the reservoir to be cooled and Due to the intense heat again repeat the cycle. of the anode I 5, and particularly at the point immediately in back of the refractory metal target, a cracking of the cooling and insulating medium frequently results and a carbonaceous deposit will accumulate not only at the point of greatest heat concentration, as before noted, but also over the remaining inner surface of the hollow anode.

Th formation of this deposit in addition to being attributable to the intense heat causing cracking of the hydrocarbon oil may to some extent be attributable to the copper per se or to the copper oxide formed thereon, and upon continued use of the tube with a resulting accumulation of carbonaceous deposit the latter eventually acts as a heat insulator due to its low heat conductivity characteristic, thus decreasing the efficiency of heat transfer.

"In order to prevent accumulation of this deposit I provide the innermost surface of the hollow anode with a layer of metal 24 of different composition than the anode, such as mirrorlike or highly polished chromium, nickel or the like, which .has an inappreciable affinity for any carbonaceous deposit which may be formed upon cracking of the cooling and insulating medium. While this layer of metal 24 in no way precludes sacracking of the oil, due to the high temperature to which the same is subjected, nevertheless because of its highly polished surface as well as its inappreciable affinity to carbonaceous deposits, the same if formed will not be tenaciously held by this layer of metal. This accordingly results in .aneflicient transfer of the heat from the anode stem to the cooling and insulating material even after long and continued use of the X-ray tube and maintains the efiiciency .of the heat transfer substantially the same as when the tube is first employed.

As a modification of my present invention I may utilize together with the cooling and insulating material, such as the hydrocarbon oils before mentioned, a liquid which has the property of removing any carbonaceous deposit from the interior surface of the anode, such for example as liquids generally termed carbon solvents.

As a still further precautionary measure I may utilize at some point in the circulatory system for the anode a suitable filter which, while permitting. free circulation of the cooling medium nevertheless functions to accumulate any of the carbonaceous deposit resulting from a cracking of the oil, and thus prevents circulation of this carbonaceous deposit through the circulatory system, with the usual result of it accumulating at the points of greatest heat concentration and causing a decrease in the efliciency of heat transfer.

It thus becomes obvious to those skilled in the art that I have provided an electron discharge tube, such for example as an X-ray tube, which may be operated in connection with the continuous generation of X-rays over long periods of time, as in the administration of therapeutic treatments, and wherein a carbonaceous deposit is prevented from accumulating at the points of greatest heat concentration interiorly of the hollow anode. Inasmuch as such deposit, which would ordinarily function as a heat insulator, is prevented from being formed at the points of greatest heat concentration the efficiency of the heat transfer from the highly heated points of the anode electrode to the oil is maintained over a long period of continued use of the tube.

Although I have shown and described several embodiments of my present invention I do not desire to be limited thereto as various other modifications of the same may be made without departing from the spirit and scope of the appended claims.

What is claimed:

1. An X-ray tube comprising an envelope, a cathode, an anode including a refractory-metal target which becomes heated during operation by electron bombardment and a hollow anode stem, and means disposed on the interior surface of said anode stem consisting of a material differing from that of said hollow anode stem and having a highly polished surface offering an inappreciable resistance to the circulation of a cooling and insulating material to prevent the accumulation of carbonaceous deposits interiorly of said hollow anode stem.

2. An X-ray tube comprising an envelope, a thermionic cathode, an anode including a refractory metal target which becomes heated during operation by electron bombardment and a hollow anode stem, means for circulating a cooling and insulating material through said hollow anode stem for transferring heat from said anode, and means disposed on the interior surface of said anode stem having surface characteristics which offer an inappreciable affinity for any carbonaceous deposit formed by said cooling and insulating material and presenting substantially no resistance to the flow thereof.

3 An X-ray tube comprising an envelope, a thermionic cathode, an anode including a refractory metal target which becomes heated during operation by electron bombardment and a hollow anode stem, means for circulating a cooling and insulating material through said hollow anode stem for transferring heat from said anode, and means disposed on the interior surface of said anode having a surface which prevents carbonaceous deposits from tenaciously adhering thereto whereby the efficiency of heat transfer from said hollow anode to said cooling and insulating material is not impaired after long continued use of said X-ray tube.

4. An X-ray tube comprising an envelope, a

thermionic cathode, an anode including a refractory metal target which becomes heated during operation by electron bombardment and a hollow metallic anode stem, means for circulating a cooling and insulating material through said hollow metallic anode stem for transferring heat from said anode to said cooling and insulating material, and a metallic coating of a material differing from that of said anode stem disposed upon the interior surface of the latter and having surface characteristics offering an inappreciable afiinity for any carbonaceous deposit formed by said cooling and insulating material and offering substantially no resistance to the flow thereof.

5. An X-ray tube comprising an envelope, at thermionic cathode, an anode including a refractory metal target which becomes heated during operation by electron bombardment and a hollow metallic anode stern, means for circulating a cooling and insulating material through said hollow metallic anode stern for transferring heat from said anode to said cooling and insulating material, and a metallic coating of a metal differing from that of said anode'stem disposed upon the interior surface of the latter and provided with a highly polished surface to prevent carbonaceous deposits tenaciously adhering thereto upon cracking of said cooling and insulating material when subjected to heat from said hollow anode thus maintaining the efficiency of heat transfer from said hollow anode stem to said cooling and insulating material after long continued use of said X-ray tube.

LOUIS F. EHRKE.