US2497543A - Deflecting and focusing means for x-rays - Google Patents

Description

Feb. 14, 1950 1.. K. FREVEL 2,497,543

DEF'LECTING AND FOCUSING MEANS FOR X-RAYS Filed Sept. 19, 1946 IN VEN TOR. Lua o K. Frei/e/ A TTORNEYS Patented F eb. 14, 1950 STATES PATENT OFFICE DEFLECTING AND FOCUSING MEANS FOR X-RAYS Application September 19, 1946, Serial No. 697,934

UNITED 6 Claims.

This invention relates to a medium for defleeting X-rays and to a condenser for focusing X-rays using the medium.

It has long been realized that efficient means for deflecting and focusing X-rays would be desirable, both in X-ray therapy and X-ray spectroscopy. Thus, a convergent X-ray beam, such as would be produced by a condensing lens, should be highly advantageous in deep-therapy work. Likewise, a focusing device, by concentrating X-rays which would otherwise be lost, should materially increase sensitivity in X-ray spectroscopy.

Simple deflection of X-rays may, of course, be accomplished by means of plane single crystals, such as those of sodium chloride. X-ray focusing has been attempted by means of bent single crystals, but the amount of bending which can be achieved is quite limited. Consequently, only a small solid angle of a divergent X-ray beam can be subtended by the bent crystal and hence only a minute fraction of the beam brought to a focus.

In addition, defects in the crystal induced by bending frequently cause troublesome diffraction ghosts.

In view of these considerations, it is an object of the present invention to provide an inexpensive medium for deflecting X-rays which may be simply prepared from readily available materials.

Another object is to provide a deflection medium parallel to the surface, the piece acts, when exwhich may be easily shaped to any de Curve, posed to X-rays, like a single crystal with reinclud a full Cy so as to Subtend a large spect to the crystal plane parallel to the surface P Of a divergent y beam and h of the molding. A part of the beam of X-rays an eificient X-ray ens-" A furt obiect 1s to falling obliquely on the surface is diffracted mp i a p e apparatus for producing a accordance with Braggs law. By curving the low convergent beam Of monochromatic surface of the piece concavely, convergence of According to the invention, an X-ray defiecpart of the incident X ray beam may be protion medium s P p by forming smooth" duced in a manner quite analogous to the consurfaced body of amorphous material having .centration of light by a concave mirror. bedded therein thin flakes of a crystalline sub- 40 The invention may be further explained with Stance, Such flakes hemg oriented Parallel to reference to the accompanying drawing, in which the Surf ace of body conveniepfly Fig. 1 is a fragmentary View of a molding press medium 15 Produced m the form of h flexlble in which a polystyrene-graphite mixture has fl f' Whlch may be curved in any deslred man, een placed, the body of the mixture being shown so far as known, there may be used i iiiglgfen line to 1nd1cate that it has considerable amorphous material which can be formed 11 o a compact body, the term amorphous referring i 2 a Vlew 9 the .press after molding to the fact that the material shows practically 3 1s Verhcal Y partly in on, of no diffraction pattern to X-rays. Amorphous apparaths for prducmg convergeht mono organic plastics, particularly synthetic resinous chromatlc X'ray beam 115m? a cyhndncal r thermoplastics such as polystyrene and ethyl condenser according to the invention, the section cellulose, are preferred because of the ease with belhg taken along the hue of 4; and which they may be shaped by molding. Fig. 4 is a horizontal section of the same ap- The crystalline material employed in the illparatus, taken along the line 44 in Fig. 3.

vention should, of course, be one which can readily be converted to the form of thin flakes. In general, flakes of inorganic crystalline substances characterized by micaceous cleavage are preferred because they are most easily oriented parallel to the surface of the amorphous ma terial by a simple molding operation. The term micaceous cleavage refers to the nearly perfect basal cleavage exhibited by the micas and other minerals, by virtue of which these substances are separable into very thin leaves. Typical of such substances are mica, talc, mercurous chloride, mercurous iodide, cadmium iodide, molybdenite, yellow lead monoxide, and graphite.

In making the X-ray deflection medium, the amorphous material, conveniently an organic thermoplastic, e. g. polystyrene, and the crystalline material, e. g. flake molybdenite or graphite, are ground separately and then mixed together thoroughly. The proportion of crystalline material is not critical, but should be as high as is consistent with maintaining good molding qualities. The mixture is then molded under heat and pressure in such manner as to cause a high degree of lateral flow in order to orient the flakes parallel to the surface of the molding. The resulting product, after removal from the cooled mold, is ready to be used.

Since all flakes in the molded piece are oriented In the procedure illustrated in Fig. 1, a mixture of equal parts by weight of ground polystyrene 5 and finely-divided flake molybdenite 6 is loaded between opposing flat plates 1 of a compression molding press in the form of a loose mass in whichcth'ermolybdenite flakes are inrandom orientation (Fig. 1). The plates are heated to a temperature of 80 to 125 C. and forced together to mold the mixture between them. Under; the applied pressure, the material flows laterally,

and the lattice constants of the flake molybdenite in the medium 2|.

The apparatus of Figs. 3 and 4 thus effectively deflects a portion of a divergent X-ray beam and focuses it into a hollow convergent beam of monochromatic rays whichqeach'es. a focus at a point belovwth'e tube I5.- Different wavelengths of the convergent beam may be secured by increasing or decreasing the length of the tube I5 the action of the flowing plastic serving to turn'.

the molybdenite flakes in the direction of flow.

When compression is cmpleted..(Fig.12):, there; is obtained a thin sheet 8 of-material inwhich all.

the flakes are oriented parallel to the surface of the sheet. In general, it is-desi-rabla'in'making a sheet of 0.010 inch in thickness, to start with a mass at least 0.5 inch in height.

If the flakes 6 are not, perfectly oriented in the first molding, the sheetB may be cut into strips, which can then be superposed and remolded;

The-final molded sheet, af-t'ertrimming; may

be rolled into cylindrical form and used as a f 0' cusing medium to produce a convergent monochromatic X-rayxbeamin theapparatus of Figs. 3 and 4.

In this apparatus',;X-;rays of a-whole band of wave-lengthssaregenerated in a conventional high-.vacuum-u. X-ray tube;. 9,: such as a type AEGl-Z50, havinga .heated cathode I0, grounded target I I, and beryllium); window I2 through which the rays issue. as.-a.adiv.ergent beam. The.

lower "end i;of :the :tube:9 fits into. a cylindrical adapter I3 .in' one side-of. which isan opening I4 concentric. with and jlargerathan the "X-ray window I2.-

Mountedon the'adapter is.:an elongatedcylindrical lead-:alloy tube I5 icosaxialzwiththe window. I2 and opening, I4; the tube beingzmade in. three: interfitting "sections.- .asxshown, for convenience. inmanufacture. In.-the upper portion of the tube I5 are .twottransverse, lead-alloy shields I6 and I1 spaced from' the window I2 :and :from. each. other. Narrowuannulanslits .dszland I91;are cut"in the shields co-axial withn-therwindow I2; The slits are of suchfli'ameterszas -1t0- i all? in the surface of a divergent t conerincluding.- .the window I2 and having its apex at. the star-get i i; Below the lower slit I3, the wall? OfthE-tllbfll-IEiiS. thickened inwardly .to provide;aacylindricalzsurface 2 0 which.

is co-axial with:and.intercepts..the surface of the cone defined by the. slits I8 and] A polystyrene-orientedrmolybdenite-flake flexible.X-ra-y deflectingnsheetflt, prepared as previdusly described, isrrolled-intoza cylinder and secured into :the tube 5 so :as to it snugly against.

in the tube I5and shield :22, but .a portion is.

diffracted-gar reflected in :the 'form of av convergent conicahbeam which is sharpened by the-1 slit -23." This difiractediportion T18 of essentially monochromatic -X-rays, the. wavelength :ofv which from thewindow .I2 to the deflecting cylinder 2| and correspondingly changing the diameters of the slits I8, I9, and 23 to alter the conical angle of the X-ray beam; Alternatively, the deflecting sheet zl' can be'removed and a new sheet containing a different crystalline flake material substituted.

The apparatus shown may be used as a source ofl a convergent X-ray beam in deep therapy, in which use it has the advantage that, by suitably choosing the wavelength. of the convergent beam, the softer X- rays, which.xproducesserious erythema; can beeliminateda';

The foregoing descriptioniissillustrative rather.

than strictly alimitativep therinyention :being coextensive in scope with ".thenfollowing 2 claims;

What isnclaim-ed is.::

1.: In combinationxwith a source of. a divergent X=rayiv beam; ashollow.:cylinder.formed ;of an.

amorphous. organic: plastics: having; embedded therein ':.thin .flakesi of: am. inorganicwcrystalline: substance characterized :by- 1, micaceous cleavage,

such .flakes: being; oriented :parallel to the surface of the cylinder, and a support fQr'the'cyI- inder disposed to maintain the axismf the cylinder in-linewith the X-ray source;

2.; Apparatus for -.providing-a hollow convere gent beam of. monochromaticvibrays comprisingz; awsourcei of a divergent X-rraybeam; a shield spaced from" the source and. having; therein an annulariislit Leo-axial with -the 'divergent beam, such shield-i acting- -to'restrict the-beam to .the form-of,a.hollow-divergentccone; and an X-ray ;.condenser.-.-comprising a. hollow cylindrical. formedtoiansamorphous organicl-plastichav ing molded therein thin flakes of an inorganic crystalline substance characterized:bytmicaceous cleavage, such flakesebeingioriented parallel to the surface ofthe cylinder-,1 anda support for the 3.; Apparatus for-providinga convergent X-ray, beam comprising asourceof a divergent X-ray beam,.amountinghaving thereon? a-hollow right.-. circular cylindrical X-raydeflector-support with itsaxis in lineew-ith..the -Xrray source 1 and so spaced from -the-so11-rce.-.that the vinside surface of. :the support intercepts vthe. -X-ray,- beam, I and an Xeray-deflectorhelement lining the support and comprising; a thin., .flexible.. sheet of an; amorphous. organic. plastic having. embedded. therein: .thin flakessofuan. inorganic crystalline substance characterized by micaceous cleavage, such flakes being. .-.oriented parallel to the surface of .the. I sheet.

4; Apparatus.- for. providing .a hollow convergent beam of. monowhromatie' X-rays comprisingz. asource of'a hollowadivergent conical X.-ray beam; a mounting havingrthereon a .hollow right-- circular .cylindricalsX-ray deflector support 00-- axialwith .the source. and-so. spaced .from= the latter that the -.inside.-.surface.of=thesupport in-.

is: fixed by the. conicaLangle ofthe divergentbeam' tercepts theshollowu. conical..-X.-ray beam, and

an X-ray deflector element comprising a thin flexible sheet molded of an amorphous organic plastic having embedded therein thin flakes of an inorganic crystalline substance characterized by micaceous cleavage, such flakes being oriented parallel to the surface of the sheet, the said element being curved to cylindrical form and'removably lining the deflector support.

5. Apparatus according to claim 4 wherein the organic plastic is polystyrene and the inorganic substance is graphite.

6. Apparatus for providing a convergent ray beam comprising: an X-ray tube having an X-ray transparent window therein; a hollow cylindrical X-ray opaque tube mounted on the X-ray tube co-axial with the window thereof, a pair of X-ray opaque shields mounted transversely in the tube spaced from the window and from each other, each shield having therein an annular slit co-axial with the tube, the slits being of such diameters as to restrict the X-ray beam issuing from the window to the form of a hollow divergent cone, a cylindrical X-ray deflector support surface formed in the tube coaxial therewith and at a point more remote from the window than the shields in position to intercept the cone defined by the slits, and an X-ray deflector element comprising a thin flexible sheet molded of an amorphous organic plastic having embedded therein thin flakes of an inorganic crystalline substance characterized by micaceous cleavage, such flakes being oriented parallel to the surface of the sheet, the said element being curved to cylindricaliorm and removably lining the deflector support.

LUDO K.

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

OTHER REFERENCES A Variable Temperature X-Ray Powder Camera, by W. H. Barnes and W. F. Hampton, Review of Scientific Instruments, vol. 6, November 1935, pp. 342-344.

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