US2473956A - Stereoscopic x-ray pictures with betatron - Google Patents

Description

June 21, 1949. D. w. KERST STEREOSCOPIC X-RAY PICTURES WITH BETATRON Filed May 29, 1946 FIG; 2

TIME

FIG. 3

' INVENTOR. DONALD W. KERST BY W ATTORNEY Patented June 21, 1949 STEREOSCOPIC X-RAY PICTURES WITH BETATRON Donald W. Kerst, Urbana Ill., assignor. to. the United States of America. as represented by the Secretary of the Navy Application May 29, 1946; Serial'No. 672,982

6 Claims.

This invention relates to X-ray systems and especially to a system forproducing: stereoscopic X-ray shadows.

Producing stereoscopic X-ray shadows is a well-known art. Furthermore, the art of producing X-rays by means of the magnetic induction accelerator,- though comparatively new; is also well known. My-- invention is a new and useful combination of these two basic arts.

It is an object of my invention to provide two simultaneous and powerful sources of X-rays by means of a single magnetic induction accelerator so disposed that. the two X-ray beams so produced cross in. a region adjacent tothe aforementioned source of X-rays. Thus two shadows are instantaneously produced from separated sources.

It is a further object of my invention to provide means by Whichthe X-ray shadow formed by the passage of X-rays through the object under exposure can be greatly enlarged and still have well-defined edges.

A better understanding of this invention, together with further objects and advantages thereof can best be understood by reference to the accompanying diagrams and their descriptions.

Fig. 1 is a schematic view suitably embodying the invention.

Fig. 2 is a partial view showing the magnetic assembly.

Fig. 3 is a curve used in explaining a feature of this invention.

In Fig. 1 there is shown a closed vessel of glass or other suitable material which defines the continuous annular chamber 5 of a conventional magnetic induction accelerator. Within said chamber 5 there is a suitable electron gun 4 for injecting two beams of electrons in opposite directions approximately tangential to said vessel 6.

In a magnetic induction accelerator, means are provided for obtaining a time-varying magnetic flux within said chamber 5. This means is illustrated in Fig. 2 wherein I6 and I! are pole pieces about which is wound a field coil I5. A voltage of the wave form 22 depicted in Fig. 3 is applied to terminals M to energize the field coil and efiect a time-varyin magnetic flux through the annular chamber 5.

The two beams of electrons emitted from the electron gun 4 are caused to be injected shortly after the voltage wave form 22 has passed through Zero. This is shown in Fig. 3 as at points [8 and 20. Of the electron beam emitted at l8, one beam is accelerated and focussed into an orbit 2 as: shown in my prior Patent 2,297,305 and. the other is deflected into the wall. At 20, the electron beams reverse the above roles.

The electron beams so vfocussed are continuously accelerated until the proper voltage is attained, such as at is and 2|, then a pulse of magnetic flux is caused to be sent through the electron orbit in the proper direction. This flux spirals one beam inward to strike target 8, and a half cycle later spirals the other beam outward to strike target 1. This: entire process occursionce during every cycle of the voltage wave- 22. The electrons which impinge on targets 1, 8 have tremendous energy thereby giving rise to the highenergy X-ray streams 9 and. to. One suitable manner in which the orbital radius maybe increased or decreased, as desired, is set forth in applieantsv patent application Serial Number 445,465, filed June. 2, 1942, now Patent No; 2,394,070.. Additional details of constructionand the manner of, operation of a suitable electron accelerator are described in an article published in the July 1, 1941, issue of the Physical Review, volume 60. Timing means for effecting injeotionof electrons at appropriate times in the magnetizing voltage cycle are further illustrated in U. S. Patent Number 2,331,788.

The nature. of vbombarded targets is, such as to produce sources ofX-rays which approximate point, sources, thereby enabling a film. l2. and 13 to be placed well behind the object ll under exposure and still enable well-defined pictures to be produced. It is desirous to place the film well behind the object becauselarge magnification is obtained thereby. As the shadow positions are important to the use of stereoscopic X-rays, a sharper edged shadow increases the systems accuracy.

This use of the magneti induction accelerator achieves a new and much more useful stereoscopic X-ray device by providing both X-ray sources in a new manner, by generating X-rays of unusually high energy, and by accelerating the bombarding electron beams with an alternating current power supply that is simple and economical in comparison to conventional direct current supplies.

Having thus described my invention, what I claim is:

1. In a magneti induction accelerator for charged particles having an acceleration chamber, means for injecting two beams of particles into said chamber, and means including targets spaced substantially on a diameter operable to intercept said beams, one of the targets being on I the inner wall of the chamber and one being on the outer wall of the chamber.

2. In a magnetic induction accelerator for charged particles having an acceleration chamber, means for injecting two beams of particles into said chamber in opposite directions, and means including a pair of targets operable to intercept said beams and positioned on the inner and outer walls of the chamber to emit generated rays in such directions as to converge outside the acceleration chamber.

3. In combination with a magnetic induction accelerator having a chamber within which electrons may move in a circular path, means for injecting two beams of electrons into said chamber in opposite directions, means for producing a transverse time-varying magnetic flux within the chamber for accelerating and focussing first one and then the other of said beams into an orbit, a pair of spaced targets in said chamber, means for deflecting said beams into said targets to generate X-rays, said targets being so disposed on the inner and outer walls of the chamber and substantially on a diameter to cause the emitted X-rays to converge on an object, and means for recording the X-ray shadows of said object.

4. Apparatus for simultaneously producing X-ray stereoscopic shadowgrams of an object including a betatron accelerator having an annular accelerating chamber, an electron gun within said chamber and disposed to emit electron beams in two opposed directions substantially tangent to the exterior circumferential wall of said chamber, magneti induction means energized by alternating current and accelerating one of said beams in a clockwise stable orbit during part of the positive half cycle of said energization, said means accelerating the other of said beams in a counterclockwise stable orbit during part of the negative half cycle of said energization, a target disposed exteriorly of said orbits for emission of X-rays when the radius of one said orbit is increased, a target disposed interiorly of said orbits and at the opposite side of the annulus and arranged for emission of X-rays when the radius of the other said orbit is decreased, said targets having the target faces thereof disposed at opposite sides of the chamber and substantially tangent to the direction of orbital motion and oriented for production of narrow intersecting beams of X-rays when bombarded respectively at grazing incidence, an object at the point of intersection of the X-ray beams, and means remote from said object for photographing the shadows cast by the X-ray beams divergent therefrom, whereby two stereoscopically related shadowgrams are produced during an exposure interval.

5. In the art of stereoscopic photography by high speed X-rays, the method of, magneticinduction accelerating electrons to very high velocity in circular orbits, modifying the orbits of part of said electrons after acceleration thereof to produce a directed narrow beam of X-rays by grazing incidence bombardment of a first target, modifying the orbits of substantially the remainder of said electrons after acceleration thereof to produce a directed narrow beam of X-rays intersecting said first narrow beam by grazing incidence bombardment of a second target, and separately photographing the shadows of an object located at said intersection.

6. In the art of stereoscopic photography by high speed X-rays, the method of, producing two oppositely directed streams of electrons, accelerating said streams of electrons respectively, in oppositely rotating circular orbits by magnetic induction, producing two intersecting narrow beams of X-rays, one from grazing incidence bombardment of one target as the radius of orbit of one said rotation is decreased and the other from grazing incidence bombardment of a second target as the radius of orbit of said opposite rotation is increased, and separately photographing at positions remote from said intersection shadowgrams of an object located in said beams at the intersection thereof.

DONALD W. KERST.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,123,942 Snook et a1 Jan. 5, 1915 2,297,305 Kerst Sept. 29, 1942 2,331,788 Baldwin Oct. 12, 1943

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