US1153290A

US1153290A - X-ray target.

Info

Publication number: US1153290A
Application number: US2040915A
Authority: US
Inventors: William D Coolidge
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1915-04-10
Filing date: 1915-04-10
Publication date: 1915-09-14
Anticipated expiration: 1932-09-14

Description

W. D. COOLIDGE.

X-RAY TARGET.

APPLICATION FILED APR. 10. 1915.

1 9 1 fi fi m o Patented Sept. 14, 1915;

lnvntovr William DQCooHolge, y WM Hi S Attorney IIWIM @TATTEd AEWT UI I @M.

WILLIAM I). COOLIDGE, 0F SCHENEOTAZD'Y, NEW YORK, ASSIGNOR IO GENERAL ELECTRIC COMPANY,A CORPORATION OF NEW YORK.

X-RAY TARGET.

Specification of Letters Patent.

Patented Sept. 1d, 1915.

Application filed April 10, 1915. Serial No. 20,409.

To all whom it may concern Be it known that I, WILLrAM D. COOLIDGE, a citizen of the United States, residing at Schenectady, county of Schenectady, State of New York, have invented certain new and useful Improvements in X-Ray Targets, of which the following is a specification.

In the operation of X-ray tubes, a stream of cathode rays, consisting of electrons traveling at high velocity, impinges on the surface of a metal body known as the target, which commonly also serves as anode. When the cathode rays strike the target surface, part of their energy is converted into X-rays but the larger part is'converted into heat. It is desirable to have the cathode rays impinge on a highly refractory metal and for this purpose tungsten is particularly suitable. The tungsten disk serving as the target proper has in some cases been embedded in a-mass of copper to increase the heat storage capacity of the anode and to carry heat away from the focal spot. When an electrode consisting in part of copper is used in X-ray tubes operating with a substantially pure electron discharge, such as described in the Physical Review for December 1913, care must be exercised not to raise the temperature far above redness, otherwise gas is evolved and copper is vaporized. A pure electron discharge can take place only when the gas pressure is not greater than a given minimum pressure, the particular value of which depends on the voltage of the discharge. As the natural cooling of a body in a vacuum at temperatures below redness proceeds very slowly, a pure electron discharge X-ray tube equipped with a copperbacked target is subject to undesirable limitations. An all-tungsten target is free from these limitations, but the high specific gravity of tungsten restricts the size of the target for mechanical reasons.

In accordance with my invention I have provided a target having a greater heat dissipating capacity than an all-tungsten target of the same weight, and which may be heated to a temperature of bright incandegcence in a pure electron discharge X-ray tu. e.

My new target consists of tungsten and molybdenum as illustrated in the accompanying drawing in which- Figure 1 is a perspective view of the target, and Fig. 2 is a sectional view.

The main body 1 of the target consists of molybdenum and the inset 2 consists of tungsten, both metals preferably being in the ductile state. The tungsten inset preferably should be accurately fitted, as by grinding, into the recess in the molybdenum, so as to get the metals into good heat conducting relations. The target should be so arranged in the tube that the cathode rays are made to focus upon the tungsten inset. The specific gravity of molybdenum is only about one-half that of tungsten and the specific heat of molybdenum is more than twice that of tungsten. Hence this new form of target has nearly double the surface and more than double the thermal capacity of a tungsten target of the same weight. The refractory nature of molybdenum enables the thorough removal of gas from the target. When used in an X-ray tube operating with a pure electron discharge substantially independent of positive ionization, the present form of target may be heated to bright incandescence without disturbing the normal operation of the tube.

What I claim as new and desire to secure by Letters Patent of the United States, is,

1. An X-ray target comprising a body of molybdenum and a body of tungsten upon which cathode rays may impinge.

2. In an X-ray tube operating with a pure electron discharge, a target comprising a body of molybdenum and a body of tungsten in good heat conducting relation thereto.

3. An X-ray target comprising a body of molybdenum and a body of tungsten mechanically fitted therein at the working face, said body of molybdenum having a substantially larger heat storage capacity than 9 said body of tungsten.

In witness whereof, I have hereunto set my hand this 9th day of April, 1915.

WILLIAM D. COOLIDGE.