US1253156A - Roentgen-ray device. - Google Patents

Description

W. D. CUOLIDGE.

ROENTGEN RAY DEVICE.

APPLICATION Fl'LED'FEB. 5, 1916.

1,253,156, v Patented Jan. 8,1918.

William IlCoolidge,

HIS DTttorneg.

UNITED STATES PATENT OFFICE.

WILLIAM D. GOOLIDGE, OF SCHENECTAIDY, NEW YORK, ASSIGNOB. T0 GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

BOENTGEN-RAY DEVICE.

Specification of Letters Patent.

Patented Jan. 8, 1918.

To all whom it may concern:

Be it known that I, WILLIAM D. Coonrnon, a citizen of the United States, residing at Schenectady, in the county of Schenectady and State of New York, have invented certain new and useful Improvements in ltoentgen-Ray Devices, of which the followmg 1s a specification.

The present invention comprises an improvement in the construction of anodes for high powered electron discharge devices, particularly targets for X-ray tubes.

Roentgen ray devices are commonly op erated with a variable current such, for example, as derived from the rectification of a high potential alternating current or when a rectifying tube is used, it may be connected directly to a transformer. In either case the heat generated at the target or anode varies in step with the energy input. In the X-ray devices operating by virtue of the ionization of' residual gas, inputs of energy large enough to cause harmful effects because of the intermittent character of the heating can be impressed upon the tube, for time intervals too short to cause damage, say for a second or two, due to 'the excessive heating of the bulb. However, X-ray tubes operating with a substantially pure electron discharge may be operated continuously without excessive heating of the bulb.

I have found that when an X-ray tube of this type is operated continuously with a relatively large energy input, for example, one or more kilowatts, that a mechanical disintegration of tearing of the anode results which is not observable with low powered apparatus. My experiments have shown that this disintegration is the result of the mechanical tearing caused by the rapid expansion and contraction takin place due to the intermittent conveyance 0 heat from the heat receiving face to the cooled section of the anode.

In accordance with my present invention the anode is preserved intact by making the energy receiving face of the anode of sufficient thickness to afiord heat storage capacity great enough to transfer the variable heat input to the actively cooled parts of the metal ata rate nearly uniform. My invent'ion is particularly applicable to an anode comprising a face plate of highly refractory metal, such as tungsten and a backing of other metal such, for example, as copper.

' My invention will be more fully described n connect on with the accompanying drawmg in which Figure 1 "illustrates an X-ray target in perspective; Fig. 2 is a cross-sectional view of the same, Fig. 3 illustrates an X-ray tube provided with a target made in accordance with my invention, and Fig. l is a detail view of a cathode Referring to Figs. 1 and 2 the target illustrated comprises a ray-receiving plate 1 consisting of tungsten or other highly refractory metal and a backing tube 2, the end wall 3 of which is in intimate heat-conveying relation to the plate 1. For example, when the end wall 3 0f the cooling device consists of copper, a desired intimate weld may be $8- cured by melting boronized copper in contact with the tungsten plate in a vacuum as described in my Patent 1,162,341 of November 30th, 1915. The copper plate 3 may then be soldered or welded to the tube 2 in any convenient way, for example, as indicated at 4. A tube 5 supported and centered by lugs 6 serves for the introduction of a cooling fluid, such, for example, as water. The

target 1 should be relatively thick as com-- pared with face plates heretofore employed in water-cooled X-ray targets. For example, in a tube capable of operating with a current of about 0.1 amperes at about 50,000 volts with currents of commercial fre uency, for example, cycles, a tungsten p ate of about i" in thickness should be used. With a plate of this thickness the heat delivery to the plate 3 is uniform enough to reduce the tearing or disintegrating efiect of rapid expansion and contraction of the backing metal, sufiiciently to give the X-ray tube a satisfactory life.

Fig. 3 shows one form of X-ray tube in which a target above described has been operated continuously for days at a time without'interruption. The tube comprises the usual glass envelop 7, an electron-emittin cathode 8, such as described in the Physic Review for December 1913' and a. watercooled anode 9 of the type above described.

The tube 2 is mounted on an iron tube 10 The cathode filament 16, Fig. 4 is'heated by a battery 17 or other convenient low'potential source. The: main current is supplied by a transformer 18, the secondary of which i connected to the terminals of the Xray tube by the conductors 19, 20. As described in the above article in the Physical Review, the tube is evacuated to a pressure so low that positive ionization of residual gas is substantially absent or negligible.

When the tube is operated with alternating current any slight amount of gas evolved from the anode is electrically precipitated by a discharge emanating from the electrode 9 when acting as cathode for a current Wave negative with respect thereto, thereby vaporizing or sputtering copper. When a unidirectional current supply is used, the focusing ring 21, Fig. 4, about the cathode is c0nstituted of copper, or other readily sputtered metal. Positive ionization of residual constant rate when vice comprising a member of soft metal offood heat'conductivity, means for cooling said member and a plate of highly refractory metal in intimate heat conveying relation to said member, said plate having a mass Which will provide a heat storage capacity sufiiciently great to transfer heat to the soft metal member at a substantially currents of commercial frequency.

In witness whereof, I have hereunto set my hand this 2nd day of February, 1916.

WILLIAM D. COOLIDGE.

operated with variable Corrections in Letters Patent No. 1.253, 56.

It is hereby certified that in Letters Patent No. 1,253,156, granted January 8, 1918, upon the application of William D. Coolidge, of Schenectady, New York, for an improvement in "Roentgen-Ray Devices, errors appear in the printed specification requiring correction as follows: Page 1, line 36, for the word of, first occurrence, read or; page 2, line 27, for the word food read good; and that the said Letters Patent should be read with these corrections therein that the sanie may conform to the record of the casein the Patent Oifice.

Signed and sealed this 12th day of February, A. D., 1918.

[SEAL] J. T. NEWTON,

Commissioner of Patent-x.

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