US1208128A - X-ray tube. - Google Patents

Description

Patented m. 12, 1916.

C. A. FRIEDRICH.

X-RAY TUBE.

APPLICATION FILED JAN.2B, 1914.

CHARLES A. FRIEDRICH, OF NEW YORK, N. Y.

lX-RAY TUBE.

Specification of Letters Patent.

Patented Dee. 1L2,- llfillfi,

Application filed January 28, 1914. Serial No. 814-560.

To all whom it may concern:

Be it known that 1, CHARLES A. FRIED- RICH, a citizen of the Empire of Germany, and a resident of New York, in the county and State of New York, have invented certain new and useful Improvements in X-Ray Tubes, of which the following is a specification.

llhis invention has reference to improvements in vacuum tubes, and pertains par ticularly to X-ray tubes. It also comprises a novel method of thoroughly exhausting large amounts of metal in such tubes.

It is the special purpose of my invention to produce such X-ray tubes that will gencrate, in an extremely high vacuum, X'rays of considerable wave length which will produce the finest details of tissues; the glass walls of my novel tubes remain perfectly cool although they arevery much nearer the anode than in former tubes; furthermore to devise such means, whereby the very massive electrodes of my new tubes may be thoroughly exhausted without creating a static field during this process of exhausting. v

It is well known to science that the wave lengths or penetration power of X-rays is solely due to the velocity with which the molecules of the residual gases are carried toward the target, thus forming the cathodal stream. Up to the present time the only factor known to govern the velocity of these molecules was thedegree of the vacuum,

that is, their velocity lncreases with the increasing vacuum. But strangely enough the highly penetrative rays of the former X-ray tubes do not produce details oftissues such as lungs, stomach, kidneys, etc. On the contrary, such details get lost entirely. Knowing this fact, the X-ray workers have adopted the technique of using X-ray tubes of low penetration to insure details, and in order to arrive at short exposures, they are passing an enormous amount of current through the tube, whereby naturally the former X-ray tubes become defective very quickly. The fact that the former highly penetrative X-rays do not produce details,

however, does not coincide with this distinct character of rays of lower penetration, because X-rays of even the greatest wave length ought to produce the finest details,

. owing to the very rnuch shorter exposures.

The practice withthe former tubes of a field will almost out out the action of the vacuum pump, so that the liberating gases of the metal parts will not only accumulate in the tube, but exist there under a certain pressure; besides, the presence of the static field does not admit these dense metal gases to remain within same, but they get forced against the glass wall, where they partly condense and so form a minute lining of metallic origin upon said glass walls. Now, if we have such a tube highly exhausted, electric leakages along the glass wall occur which will impart a secondary motion upon the waves of X-light and so make them lose their original character of producing details of tissues.

In order not to obstruct the action of the vacuum pump and also to avoid the pres ence of condensed metal vapors upon the glass wall, I have devised a special method of exhausting tubes by using such other heat sources that do not create a static field in the tube during the time the metal attains red heat. So, for instance, 1 construct my anode hollow and insert a special electric heater into the hollow space, thus being able to heat any amount of metal in a very short time to the desired degree of heat. To enable me to also exhaust thoroughly the cathode, I make provisions for a heating device for this electrode whereby I am able to heat the very massive cathode to red heat without. the presence of a static field.

A further advantage ofmy newly devised method of exhausting is the fact that by not using any high potential current during the manufacture of my tube, 1 preserve the formation of the path for the cathode discharge for [the individual wave of the operators generator.

Knowing from experience that two X-ray generators of the same make will not deliver an identical wave, it is evident that if an cathode discharge is formed according to discovered that this curing of a tube means the manufacturers high potential wave, and .if such a finished tube is used on different installations, then the path of the cathode discharge, formed in the manufacture, does not suit the different wave of the operators generator and disturbances will take place within the tube in the form of high potential leakages. These phenomena being the cause that the former new tubes had to be cured or seasoned first, I have nothing else than to gradually form a new path for the cathode discharge with the operators' own high potential Wave.

In experimenting with tubes exhausted by my novel method and in which the electrodes were thoroughly exhausted, I found that I could not get the discharge to readily take place between the anode and the cathode, but it would occur from the part of the electrodes nearest the glass wall along the same.

In exhausting my style of tubes, I took special precautions to-avoid any condensation of metal vapors upon the glass wall whichwould have accounted for the discharge taking place between the electrodes along the glass wall. The presence of-this phenomenon, however, without any perceptible deposit of metallic origin upon the glass wall, has led me to the supposition that the molecules of the residual gases in a vacuum tube are not uniformly distributed, but the molecules nearest the glass wall are rather dense, gradually getting rarer toward the center of the vacuum space. In other words these gas molecules are suspended in the space concentrically. For this reason I have devised in my new tube an entirely different position for my cathode, that is, I

place that electrode in the center of the vacuum space and so prevent it from discharging through the denser gaseous mole cules along the glass wall. By placing the cathode in this position the electric resistance between the electrodes will decrease from the cathode toward the anode, quite contrary to the former tubes. This decrease of the resistance toward the anode is due to the fact that the position of the cathode, being in the rarest vacuum while the anode or target is surrounded by considerably denser gases.

The foregoing theory is borne out by the fact that the tubes described in the last paragraph would not discharge between anode and cathode at first, as the electrical resistance of the denser gases along the glass wall is considerably less than that of the much shorter way between anode and cathode where the residual gas molecules are extremely rare. However, as soon as both elec- -up the gaseous molecules between the electrodes, whereby naturally their electric resistance fell below that of the much longer way through the denser gases along the glass wall. The fact that the metal parts within the tube have been brought to a much higher degree of heat during the exhausting process is ample proof that further gases have not been liberated. Furthermore, after the tube cools down, the previous conditions are reestablished, which could not have been the case if gases would have been liberated by overheating the electrodes. These tubes are neither provided with any regulating device that may absorb any such liberated gases. Further research work has also convinced me that those denser residual gases toward the glass wall offer a considerable resistance to the X-waves and in order to cut down this resistance as much as possible, I devised a diameter of only two inches for my new tube. In doing this I provide conditions which will not admit a large difference of density of the gaseous molecules between the glass wall and the electrodes, consequently the X-waves find practically no resistance within the tube.

The HbOXe facts show clearly that the path of discharge of the former X-ray tubesis much too long, considering the enormous resistance of the extremely rare gaseous molecules suspended between the electrodes. The electric discharge and the cathodal stream being two distinct phenomena, yet, in the former tubes, parts of their respective paths of motion are forced into the same path and so are bound to disturb each other. To eliminate this primary disturbance, I entirely separate, in my new tube, the path of discharge from that of the cathodal stream by providing an auxiliary discharge electrode consisting of a metal tube that fits over the anode proper and extends to within 7 mosses certain potential before it will discharge. As the gaseous molecules are started upon their path by the cathodal discharge, their velocity must be proportional to the poten ity of the gaseous molecules, I have devised.

a cathode of very large capacityv and as the distance between the anode and the cathode in my tube is only about one-eighth that of the former tubes, it is evident that this increased cathode potential will admit of a much more rapid discharge Within this extremely short distance and consequently carry along the gaseous molecules much faster.

In all these experiments I have found that the desired velocity of the gaseous molecules could only be obtained by the above factors combined with an extremely high vacuum and with the metal parts thoroughly exhausted.

The new tubes of the construction hereinbefore described and thoroughly exhausted would, even with the considerably lower electric resistance and the higher cathodepotential, not discharge properly, except by heating the electrodes as before mentioned enormous wave length and consequently very powerful.

From the foregoing it is evident that even a very short path of discharge still oflers too high an electrical resistance in an extremely high vacuum, but by heating both electrodes to a red heat, the residual gases between cathode and anode become heated too whereby the electric resistance falls to the extent where a proper discharge is established.

In these experiments a very strange phenomenon presented itself to me, that is, the more I heated the electrodes, the more current was passing the tube without changing the potential of the current itself. Also the velocity of the gaseous molecules and the penetration power of the X-rays in- .creased at the same ratio by applying a higher potential to the tube. But as there is a rather low limit to the heating of the electrodes, I have devised a special heating element for the cathode which primarily serves to heat the cathode to red heat during the exhausting and also in the finished tube toheat the-gaseous molecules between the electrodes to a point wherethe electric used for the anode. and the Xrays thus generated were of discharge will take place readily. This heating element consists of a spiral filament and is suspended, electrically insulated, from the cathode-and part of it being in such a position between the electrodes that it will neither interfere with the electric discharge nor the cathodal stream. As a heating source for this filament I use the street current in conjunction with a suitable rheostat thus enabling me to heat the residual gases between the electrodes to a very fine degree, thereby obtaining X-rays of any desired wave length. In experimenting with such tubes, I also found that the inverse currents set up in high potential generators cannot discharge between the electrodes but only those impulses of electric energy will pass the tube that make the cathode the'negative electrode. The cause of this phenomenon is that the molecules of the residual gases within the path of the negative discharge are so highly heated up that the low electric resistance thereby established will admit of an easy discharge. However, the heating filament, being a considerable distance from the positive discharge electrode, will not heat up the gaseous molecules within the path of the positive discharge at the moment the anode is made the negative discharge electrode.

In order to make my new tube withstand the terrific impact of the enormously fast moving gaseous molecules, I construct my anode hollow, that is, open to the atmosphere so that it may conveniently be cooled; furthermore, about two pounds of metal are Of late X-rays are being used extensively for the treatment of malignant diseases and to prevent the superficial tissues from getting injured, filters of aluminum are used outside the tube, so as to prevent the dangerous rays of. a short wave length to reach. the patient. In my new tube I make use of the auxiliary anode first to protect the operator from the ill effects of the extremely powerful rays, and secondly, to filter the X- waves within the tube by means of a suit able metal window, thus my new tube can be used without further precautions for treatment work. For X-ray treatment it is also desirable that thetube be brought very close to the patient and as I have for other reasons devised a very small diameter for my tube, I can safely bring the glass wall of my tube in actual contact with the patients body, especially as the glass wall remains absolutely cool. In treating malignant diseases with the glass wall of my new tube in actual touch with the patients body, I obtain very efiective therapeutic values.

In order to render the invention entirely olear'reference is had to the accompanying drawing 1n''wh1ch:

v Figure 1 represents 1n longitudinal elevadescribed hereinafter.

tion, partly in section, an X-ray tube embodying in desirable form the present improvements. Fig. 2 shows in longitudinal section, on an enlarged scale, the cathode with portion broken away. Fig. 8 illustrates in elevation, partly in section, a water cooling device. Fig. 4! represents a special heating device in longitudinal elevation.

Similar characters of reference denote like parts in all the figures.

In the drawing, in Fig. 1 a represents a somewhat compressed glass bulb in which the curved large top portion 1) of the oathode, constituting the discharge electrode, is located. The lower narrower portion 6 of the cathode extends into the tube a joined to the bulb a. The tube a is considerably less in diameter than the bulb a and has on its lower portion a tubular lateral extension 0 which is provided for the purpose of introducing the feed wires 03 of a special heating device located within the cathode and to be Atthe lower end of the tube 0 a narrower tube 6 is joined which houses a tightly fitting split metal tube, preferably a split steel tube f. This tube acts as a substantial support for the entire massive cathode. To the bottom end of the tube f is soldered or brazed a substantial lead wire 9 which in turn is fused to a platinum wire 72. that passes through the rounded off bottom portion of the glass tube 6.. A narrow glass tube 71 is fused to a somewhat wider glass tube j. In these "tubes the entire anode mechanism is mounted by means of a split steel tube is and the tube j is then joined to the top portion of the glass bulb a.

The massive cathode preferably is made of aluminum. The cathode has centrally a bore or opening 6 in which part of the special heating device is located. This mecha nism is shown on an enlarged scale in Fig. 2 and comprises the heating device connected to the leads d which leads are held separate by some solid glass 01 fused around the same.

The, leads connect with a spiral filament Z made of some metal of av high fusion point,

such as platinum, tungsten and the like. One of the leads is surrounded by an insulating glass tube m and therefore will prevent the lead wires from forming a short circuit. Both leads are separated from the inner cathode walls by a silica tube 92. on the upper portion of which the spiral Z is wound. A small split steel tube 0 is mounted in the lower portion of the cathode by means of a bent wire 0 as shown. Said steel tube 0 serves as a support for the whole heating device. The leads (1 being held apart by means of an insulating glass tube m require two small openings in-the silica tube 12. for the purpose of rendering it possible to connect said leads to the free ends of the spiral Z.

The anode ismounted bymeans of the 1,2os,1es

glass tube 2' as previously stated. The anode body ;0 is provided at its lower end with two rings 9 shrunk thereto. Centrally on the slanting surface of the bottom end of the anode there is a block of silver 1" faced with platinum. To prevent the crossing of the electric discharge and the cathodal stream these are separated by providing an auxiliary discharge electrode in form of a'metal tube 8 that is secured to the anode proper and reaches down to about one-half an inch from the cathode. This auxiliary electrode is provided with sharp points 7'. To effect the filtration of the X-rays within the tube a metal window 8 is provided in the tube 8 in the path of the active rays. The short path for the electric discharge thus created is adapted to increase considerably the velocity of the gaseous molecules. The anode is constructed hollow for reasons hereinbefore stated, that is, it is open to the atmosphere and may conveniently be cooled by means of a cooling device illustrated, on an enlarged scale, in Fig. 3. This device comprises a tube t through which the water flows into the hollow "anode. This tube has a small spiral t at its bottom contacting with the block of silver 7" of the anode. when inserted, and the 'upper end of the spiral t extends into the copper loop 25 The water flows through the hollow anode and leaves through the tube 8 This arrangement is tightened within the anode by means of a rubber stopper a. In order to close the inner space hermetically a platinum ring o connecting with the anode body has fused around its upper surface glass from both sides and is joined to the top of the glass tube 2' in the usual manner. This water cooling device may be conveniently removed and inserted because it is held in position solely by the rubber stopper M. This device is used only for prolonged treatment. For radiographic purposes, for instance, this device is replaced by a mere contact spring slipped into the hollow anode. For the purpose of creating an extremely high vacuum the anode also is heated during the process of exhausting the same. Such a special heating device is illustrated, on an enlarged scale, in Fig. 4. It com'prisesan insulating tube m with heating spiral m which is electrically heated by means of'the leads 3 of which the lead 3 is insulated until it reaches the spiral :11. may be placed into the hollow anode during exhaustion in the same manner as the water cooling device. In this way a thorough exhaustion of the metal is efiected. This heating of the anode, which is composed of about two pounds of metal, insures a perfect expelling of allthe gases therefrom, that is,

the metal is thoroughly exhausted.

I claim as my invention: 1. The method of expelling the gases in split steel tube which fits closely into the X-ray tubes which consists in the produc- This device.

tion of heat within the hollow anode and cathode, thereby avoiding the creation of a static field during the periods of time when the metal parts of both electrodes attain a red heat.

E2. The method of expelling the gases from large amounts of metal in X-ray tubes dur ing evacuation which consists in the production of heat within the hollow anode and cathode, thereby avoiding the creation of a static field during the periods of time when the metalparts of both electrodes attain a red heat and efiecting thereby a thorough exhausting of the large amounts of metal of which the electrodes are composed.

3. The method of expelling the gasesin X-ray tubes which consists in creating the cathode discharge from the center of the vacuum space and producing heat within the hollow anode and cathode thereby avoiding the creation of a static field during the periods of time when the metal parts of both electrodes attain a red heat.

4. The method of expelling gases in X- ray tubes which consists in creating a very short path for the electric discharge, starting the cathode discharge from the center of the vacuum. space and producing heatwithin the hollow anode and cathode thereby avoiding the creation of a static field during the periods of time when the metal parts of both electrodes attain red heat.

5. The method of expelling gases in X- ray tubes which consists in creating a cathodal discharge, from the center of a large surface and over a very short path, starting the said-cathode discharge from the center of the vacuum space whereby uniform conditions are created both for the cathode an anode discharges. i

6. The method of operating X-ray tubes which consists in starting the cathode dis charge from the center of the vacuum space and producing heat within the hollow anode and cathode thereby heating the gaseous molecules in the path of the electric discharge to facilitate the said discharge and thus avoiding a partial discharge along the glass wall.

7; The method of operating X-ray tubes which consists in creating a .very short path for the electric discharge starting the cathode discharge from the center of the vacuum. space and producing heat within the cathode thereby heating the gaseous molecules in the path of the cathode discharge to facilitate the said discharge and thus avoiding a partial discharge along the glass wall.

8. The method of operating X-ray tubes which consists in creating a cathodal discharge from the center of a large surface and over a. short path, starting from the center of'the vacuum space and producing heat within the hollow cathode thereby heating the gaseous molecules in the path ot the cathode discharge to facilitate the said dis charge thus avoiding a negative charge on the glass wall.

9. The method of operating X-raytubes which consists in starting the cathode discharge from the center of the vacuum space and producing heat within the cathode and somewhat beyond the latter toward the anode thereby heating the gaseous molecules in the path of the cathode discharge to facilitate the said discharge and thus avoiding a negative charge on the glass wall.

10. The method of operating X-ray tubes which consists in creating a very short path for the electric discharge, starting the cathode discharge for the center of the vacuum space and producing heat within the oathode and somewhat beyond the latter toward the anode thereby heating the gaseous molecules in the path of the cathode discharge to facilitate the said discharge and thus availding a negative charge on the glass wa 11. The method of operating X-ray tubes which consists in creating a cathodal discharge from the center of a large surface 'over a short path, starting from the center of the vacuum space and producing heat within the cathode and somewhat beyond the latter toward the anodethereby heating the gaseous molecules in the path of the cathode discharge to facilitate the said discharge and thus avoiding a negative charge onthe glass wall. 7

12. The method of operating X-ray tubes which consists in separating the electric discharge from the cathodal stream and creating a very short path for said electric dis charge whereby interference with the length of the path of the cathodal stream is avoided and the velocity of the gaseous molecules increased. c

13. The method of operating X-ray tubes which consists in separating the electric discharge from the-cathodal stream and dividing said electric discharge into a multiple of separate discharges over a very short path whereby interferencewith the length of the path of the cathodal stream is avoided and the velocity of the gaseous molecules increased. I

14. The method of operating X-ray tubes which consists in separating the electric discharge from the cathodal stream, dividing said electric discharge into a multiple of separate discharges over a very short path, and producing the cathode discharge from a large surface increasing thereb the cathode potential considerably, sai in creased cathode potential eflecting very rapid cathode discharges and, also, imparting a very much higher motion to the residual gaseous molecules forming the cathodal stream.

15. The method of operating X-ray tubes which consists in separating the electric discharge from the cathodal stream, dividing said electric discharge into a multiple of separate discharges over a very short path, and producing the cathode discharge from a large surface increasing thereby the cathode potential considerably, said increased .cathode potential effecting very rapid cathode discharges and, also, imparting a very much higher motion to the residual gaseous molecules forming the cathodal stream and heating the gaseous residue between the electrodes to form a conductive bridge.

16. An X-ray tube comprising a massive cathode with large discharge surface,and an anode with an auxiliary discharge device having a multiple of pointed ends located in close proximity to the discharge surface of the cathode. p

17 An X-ray tube comprising a massive cathode with large discharge surface and having a central bore, an electric heating device located in said bore of the cathode for the purpose of facilitating the cathode discharges. V

18. An X-ray tube comprising a massive cathode with large discharge surface and having a central bore, an electric heating device located in said bore of the cathode for the purpose of lowering the electrical resistance between anode and cathode and of heating up the residual gaseous molecules .forming the cathodalstream.

said heating device being adapted to heat the cathode from inside durin exhaustion and to heat the residual gas m0 ecules within the path of the cathode discharge during operation.

20. A vacuum tube having a very massive anode and cathode close to and substantially at the same distance from all the adjoining glass wall portions with the cathode in the center of the vacuum space, and means for heating the electrodes by a low potential current to prevent creation of the static field to greatly expand and diminish the residuary gaseous molecules whereby a rather uniform density of gaseous residue is produgiad between the electrodes and the glass wa Signed at New York, N. Y., this 27th day of January, 1914.

CHARLES A. FRIEDRICH. Witnesses:

MARIE R. LEAHY, ELIZABETH KRAMER.

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