US2452045A

US2452045A - X-ray apparatus and method for crystal analysis

Info

Publication number: US2452045A
Application number: US609694A
Authority: US
Inventors: Friedman Herbert
Original assignee: Individual
Current assignee: Individual
Priority date: 1945-08-08
Filing date: 1945-08-08
Publication date: 1948-10-26
Anticipated expiration: 1965-10-26

Description

Oct. 26, 1948. H! FRIEDMAN 2,452,045

X-RAY APPARATUS AND METHOD FOR CRYSTAL ANALYSIS Filed Aug. 8, 1945 s Sheets-Sheet 1 HERBERT FRIEDMAN Oct. 26, 1948 H. FRIEDMAN 2,452,045

X-RAY APPARATUS AND METHOD FOR CRYSTAL ANALYSIS Filed Aug. 8, 1945 3 Sheets-Sheet 2 HERBERT FRIEDMAN Oct. 26', 1948. H. FRIEDMAN 2,452,045

X-RAY APPARATUS AND METHOD FOR CRYSTAL ANALYSIS Filed Aug. 8, 1945 3 Sheets-Sheet 3 HERBERT FRIEDMAN Patented Oct. 26, 1948 OFFICE X-RAYAPPARATUS AND METHOD FOR CRYSTAL ANALYSIS Herbert Friedman, Arlington, Va.

Application August 8, 1945, Serial No. 609,694

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 O. G. 757) .6 Claims.

My invention relates to an apparatus and method for developing Xray diffraction patterns of -materials and particularly to an apparatus and method for the production of patterns of much improved intensity and definition.

In my prior Patent No. 2,386,785, filed July 28, 1942, I disclosed a method and apparatus for scan ning rapidly the X-ray diffraction pattern of a material which method involves using a Geiger- Muller type of counter as the device for the detecticn of the separate lines of the pattern.

A general principle which it is desirable to follow in the production of X-ray diffraction patterns is to employ focused beams of substantially monochromatic X-rays in order to obtain intense patterns and sharp resolution of the lines constituting the pattern. Accordingly, it is an object of my invention to provide a specimen mounting device and holder for employment in a method of producing X-ray diffraction patterns of improved intensity and definition.

It is another object of my invention to provide a method of producing X-ray diffraction patterns of very sharp resolution using focused radiation in the practice thereof.

Other objects and advantages of my invention will in part be obvious and in part appear hereinafter inconneotion with the detailed description of the principle and several embodiments thereof taken in conjunction with the drawing of which:

Figure 1 represents a schematic diagram to show the geometrical relationship among the several parts of a spectrometer employed according to the principles of my invention;

Figure 2 is a horizontal sectional view of a series of specimen mounts to show the general form used to accomplish focusing in the development of a pattern;

Figure 3 is a side elevation of the holder for the specimen mount;

Figure 4 is a front end view of the apparatus shown in Figure 3;

Figure 5 is a sectional view of the apparatus shown in Figure 3 and is taken along the line 5-5 in Figure Figure 6 is a sectional view corresponding to that of Figure 5 of a modified form of the apparatus shown in Figure 5;

Figure '7 is an endview of the apparatus shown in Figure 5; and

Figure 8 is a sectional view taken along the line 8-8 of the apparatus shown in Figure 5.

In the development of a difiraction pattern, as stated, it is highly desirable that the X-ray beam used to irradiate the material being studied be substantially monochromatic in order that the amount of background in the pattern be reduced to a minimum. Various means can be adopted for so doing, among which are the conventional devices of filtering the X-rays originating in the tube by directing the radiation through a metal screen having an atomic number lower than that of the anode metal of the tube, thereby filtering out all but the a radiation of the anode metal of the tube. In my copending-application, Serial Number 609,695, filed of even date herewith, I have disclosed a method and a device for monochromating X-rays, without filtering, and simultaneously focusing the beam, which method'comprises irradiating a focusing surface which has been coated with crystallites having strong selective reflectivity for a certain wavelength of radiation.

By observing the proposition that all angles inscribed in an arc of a circle are equal, it is possible to develop an-X-ray diffraction pattern of a material in a manner such that the diffracted beams constituting lines of the pattern are focused sharply. The materialto be studied is formed as a circular arc and is irradiated by a divergent beam from a point source of radiation lying on the circle which is an extension of the arcuate specimen. The focused diffracted beam forming the Bragg angle corresponding to the angle of irradiation is then found on the same circle at a point the same distance from the specimen as is the source of radiation. By providing for irradiation of the specimen from all angles in a quadrant, all diffracted beams in a quadrant can be detected at their respective focal points. These statements have referred to a point source of radiation, a specimen which is an arc of acircle, and a focal point of a diffracted beam, but it will be apparent from the discussion hereinafter that employment of a line source of radiation and a specimen which is a section of a cylinder will give a focused line of diffracted radiation. That is, discussion of the plane geometry of the method should not be considered as limiting themethod for the plane merely repsents a horizontal section through an apparatus employing the method. i

Reference to the Bragg diffraction law spacing, and 0 the angle of diffraction, indicates that in order to develop a complete pattern, it is necessary to irradiate the specimen at angles varying from zero through 90 in order to detect all the diffracted beams to be found in a single quadrant. Starting from equal to zero degrees it is apparent that rotation of a specimen about an axis lyingin the surface of the specimen in a beam of radiation will develop its complete pat tern. If the specimen be arcuate, focused diffracted beams Will be found at appropriate points along a focusing circle as will be explained in greater detail in connection with Figure 1.

For a better understanding of the principle of my method of taking X-ray diffraction patterns and the construction and arrangement of the apparatus of my invention reference should :be a.

had to Figure 1 in which the geometrical relationship among the several parts of an X-ray spectrometer has been illustrated. In the drawing, l0 represents a point or line source of X-rays such as the anode Illa of an X-ray tube, II the beam originating at the anode and .12 afocusing monochromator, which is described in greater detail in my copendin-g application, Serial Number 609,695. The focusing monochromator refleets the beam l3 therefrom and focuses it at M. It is to be noted that these Points, I0 and I4, lie on a circle [5, arc-of which is defined by monochromator 12. The focused beam [3 is substantially monochromatic and has its focal point at 14 whereas the beam originating at H) contained all wave lengths of the X-ray spectrum of the anode metal of the tube.

Thus the point I can be treated as a point or line source of monochromatic X-rays. It should be understood that the monochromating of the I X-ray spectrum is not indispensable to the production :of a diffraction pattern. The method and apparatus indicated in the figureare merely illustrative of one way of mcnochromating an X-ray beam which makes possible the irradiation of a material with substantially monochromatic X-rays to produce apattem having very littlebackground. Actually, 14 may be considered to be a primary source of X-rays originating at an X-ray tube anode Ma.

.Using 14, therefore, as an X-ray source, the

divergence of the beam .I-5 can be controlled by passing it through a small slit 16 prior to permitting it to irradiate a specimen i! which is. mounted with an axis .of rotationat T8 in a holder like that to be described in connection with Figures 3 through 8,. The focused diffracted beam I9 is reflected from the specimen at a specific angle and the formbf the specimen mount is such-that it produces focusing of 1a difiracted beamfor those certain angular positions correspondlng to the points at which the diffracted beam forms the same angle with the specimen surface as does the axis of the primary beam. The diffracted beam will be focused at agpoint 2l on an arc of a circle 22 which has its radius equal to the X-ray .source-to-specimen distance and its center at Hi, the axis of rotation of the specimen.

It will be noted that in order for the diffracted beam (9 always to be focused substantially on the-fixed circle 22, a variation in the curvature of the specimen mount I! will be necessary for a condition necessary for focusing is that specimen H be of the same radius of curvature as the circle passing through 111-, 4a and 2| designated the focusing circle. In the drawing, three .positions of the specimen mount are indicated 01, 02, 03. The first position 01 is that in which 6 is substantiallyzero degrees and has the specimen mount substantially aligned with the axis of the beam l5. Accordingly, for a specimen having such angular relationship to the beam [5 to produce focusing of a diffracted beam on the fixed circle 22 it would be necessary for the specimen mount to have an infinite radius of curvature. or, in other words, to be a plane section like that shown in position 01. After the specimen has been rotated to position 02, a focused diffracted beam 19 for that Bragg angle is found at point 2! on the fixed circle, which point defines an angle twice the angle formed by the beam axis and the plane of the specimen. In order for the diffracted beam'to be focused at 2| on the circle 22 when the specimen forms an angle 02 with the axis of beam 15', therefore, it is essential for the specimen to have a certain radius of curvature defined by the circle passing through points l4,

Likewise, considering a'further rotation of the position of the specimen in the development of its diffraction pattern, when the position reached is that indicated as 0:; in the diagram of Figure 1, it appears that in order to produce the focusing. of the diffracted beam .23 on the circle 22 at 2! it is necessary that the specimen have a different radius of curvature of the focusing surface to match the amount of rotation of the position of the specimen. To this end the specimen should have a curvature such that it forms an arc of a circle passing through points l4, [.8, 24.

The geometry requires that the combinations of points l4, 18, 2| and l4, i8, 24, respectively, lie on circles. For convenience in taking a pattern, the position of the third point is varied through a quadrant defined bythe spectrometer bracket 25. It is apparent, therefore, that an infinite number of circles could be drawn through the sets of points should a circle be drawn for each variation in the position of the third point. To arrive at a practicable solution, it is necessary only to provide specimen mounts adapted to focus rays on the circle 22 within a certain tolerance of error and the deviation of the locus of the focal points of diffracted beams from circle 22 is compensated bythe aperture of detector 26'.

Accordingly, by providing a set of specimen mounts 17, shown in Figures 2, 2A, 2B, 2C and 2D, whose radii of curvature are varied over a range so that each specimen mount corresponds in' curvature to the circle drawn through the three points, the source of the X-rays, the axis of rotation, and the focal point of the diffracted beam. The third point is made to take a series of positions along the arc 22 and the effect of substantially continuous variation of the radius of curvature of the specimen mount and continuous focusing of the diffracted beams along the are 22 as a diffraction pattern is developed can be obtained with a minimum of error.

In Figure 2 there are shown three specimen mounts in section for employment in a diffraction apparatus in which the source-to-specimen and specimen-to-detector distances are equal to about'20 centimeters. In Figures 2 and 2A the face of the specimen mount and a vertical section thereof are shown. Figure 2 shows the face of the mount is depressed to define a specimen-receiving depression and the other figures indicate gradation in the radius of curvature. In the employment of specimens for making diffraction patterns according to this invention it is essential that the surface of the specimen being irridiated, which is a portion of a cylinder, contain the vertical axis of the specimen support as an elefor so maintaining the specimen during the tak-' ing of'the pattern will-be explained in more detail in conjunction 'with the description of the specimen holder.

Referring to Figure 3 which is a side elevation of an elementary specimen holding-apparatus, represents the vertical shaft of the holder having an axis of rotation [8. As pointed out in connection with Figures 1 and 2, it is essential that this axis of". rotation of the specimen holder pass through the surface of thefocusing specimen mount. In the drawing 32 represents a horizontal member which is cut to 'IBCGWB keyed holder 33 as shown in greater detail in adjacent Figure 4.

Points

34, 35, and 36, 31. of the holder, which are the ends of

lips

38 and 39 define fixed points on the circular arc of the specimen mount and it is. desiredth'atthe arc defined by the curvature of the specimen mount not only pass through those two pairs of points but alsothat the height of the are from the chords connecting the points be such that the axis l8'of the. holder lie inthe surface of the specimen, or form an element thereof. Accordingly, in the placing of a specimen mount in the holder, plunger 40 is provided in order to retain a specimen mount firmly and accurately within the holder in the position defined. Because the specimen mount .will require a difierent radius ofcurvature for the different positions which it will assume in the development of a diffraction pattern by rotating it through 90, a positioning device is provided in the form of a micrometer 4| for positioning a specimen mount to make the surface of the specimen include as an element the axis of rotation 18 of the holder.

Spring member 42 indicates a means for maintaining the support 33 for specimen mount l1 closely juxtaposed against the'positioning element 4| to minimize errorwhich might arise from its misalignment. Likewise spring member 42 and bearings 43 are provided in order to supportplunger 40 in a horizontal position so thatthe thrust on the specimen mount will be horizontal. J

in:section,.the apparatus shown in Figure 3 where the several elements are identifiable by correspondence in numbers. In Figure 5 a specimen mount I! has been shown in place and aligned correctly to have the surface Ila of the specimen mountedthereon coincide with the axis of rota tion I8 of the holder. As will be noted the specimen mount or backing material urges the,

plunger 40 inwardly and accordingly the resultanti force exerted by the spring 45 retains the arcuate specimen mount I! closely within the defined area with the arc incontact with the two pairs-of points 34--'35 and 36-3'l. Horizontal adjustment of the position of the specimen mount can readily be made by means of positioning ele-.

ment 4| in order to place it in a position such that the axis of rotation I8 of the holder lies in the surface-being irradiated as an element thereof.

When a set of specimen mounts of progressively varying curvature is employed, the measuring element can "be calibrated directly in terms of the several specimen mounts.

certain points on the scale in order that the position of the mount can be readily adjusted in theholder to maintain. the loci ofthe; focal points,

v That is, the speci-, .f menmounts can be numbered to correspond to of the focuseddiilracted beams an are corre sponding to 22 inFigur'e 1.

F In Figure 6v there is'shown an apparatus in which the positioning element and the plunger are combined'in the specimen holder to providefa unitary structure 'for'positioning the specimen mount. In thedrawing, 6|! represents the positioning 'elementand 6| the mount or support therefor which holds it in a fixed position on the horizontal member 32. The measuring or the moving barrel portion of the positioning element is represented by fiz'which is partially in section in order to show the interior structure thereof which permits the mounting of a plunger 40- 1 therein. The plunger 40 is fitted within the barrel 62 by means of sleeve 63 and

bushings

64 and 65.

Thespring member 66. retained in position coaxially with theplunger isshown as abutting against interior bushing 64 in the barrel. The specimen; mount I1 is shown in position with the material constituting the specimen to be examined placed so that the axis of rotation 58 of the mount passes. through thesurface Ila, thereof. When in such: a position, it isnoted that the plunger 40 is forced back and the spring 66 is compressed whereby the specimen mount His positively urged forward to engage closely the

points

34, 35 and 36, 37 in order.

that the specimen mount itself will coincide exactly with an arc of the circle defined by the source of Xerays, the axis of rotation of. the mount, and the focalpoint of the diffracted ray.

In Figures '7 and 8 there are shown an end view and top elevational section, respectively, of the holder and specimen mount in position as shown inFigures 5 and. 6. It Will'be seen that theopera tion of'thedevice is such thatthe specimen mount is always urged into contact with the, two pairs of points 3435 and 36- 3! on the specimen retainer 33 which points in turn are placed on the defined circle by-adjustment of the height of the arc; defined by the arcuate specimen mount itself In this manner, focusing of the difiracted beam along a given fixed circle 22 (Figure 1) defined by the spectrometer. bracket and the locus of the ,detector 23 is consistently accomplished.

Consideration of the geometry of the spectrometer table top and the relationship of the parts will indicate clearly that the radius of the circle defined by the point source of X-rays, the axis of rotation of the mount, and the focal point of the diffracted beam does not remain constant bututhat, as the specimen is rotated about axisl8, the radius of curvature diminishes from an infinite value when 0 is zero degrees to a minimum value when 0 is Accordingly, allowance must be made therefor in the development of a diffraction pattern in order that serious error will not'be made in detectingthe focused diffracted beam by scanning a quadrant defined by the' spectrometer bracket 25. If the dimensions of the apparatus be made large and the width of the specimen be made small it can be shown mathematic'ally that the specimen will at no time deviate seriously from a short arc, so that, by proper placing'ofthe detector, substantially focused diffracted beams will be detected by moving the detector through the arc defined by the bracket of the spectrometer. However, in precision work, such a compromise is impracticable and some reasonable approach to continuous variation of "of the lines of the pattern be made. This be comes particularly necessary --whenrit isdesiredc to bring out the more obscure lines "of a pattern! By using a specimen having a large areaand a series :of specimen mounts like .those Shown i Figure 2-, each havingthe same totalarea as the other-but each having a slightly .difierent radius of curvature to correspond to a series of positions throughout the range of positions taken by the mount in the development of a-difiractionjpattern, a -.very intense pattern can :be developed in which 7 even the minor lines are brought out sharply by virtue of the combination of irradiat ing-the. large area and focusing the beam diffracted therefrom.

Referring to Figure l where the geometric relationship of the elements of an X-ray spectrometer'hasbeen shown, it will be apparent that in the rotation of a specimen-through-QW tordevelop its diffraction pattern, changes in its radius ofv curvature are necessary. For maintenance :of

perfectprecision and-keeping the focal-point of a diffracted beam on the circle '22 a continuous change in the radiusof curvatureof'the specimen holder "to correspond exactly to that of the circle defined by the :points M, 8 and a point on .the quadrant 22 would be necessary. .A practicable compromise of the difficulty of providing for continuous change of the radius of curvature of the mount is adopted by providing a series of specimen mounts having different radii of curvature tobe used in a series of progressive positions through the series "taken 'by the specimen as it is rotated to develop its diffraction pattern. By placement of the-difir2cted beam detector close to .the circle 22 andadjustment of the radii of curvature of the several specimen mounts so that the focal'point of the diffracted beam does not deviate'farther from the focusing circle 22 than the location of the entrance to the diifracted beam detector, 2. close approximation to continuous variation of the radius 'of curvature of the specimen can be made. It is readily shown that byrproviding a series of curved specimen mounts to correspond to 5 rotations of the specimenin the development of a diffraction pattern, errors in the deviation :of the focal 'point of the diffracted beam from the circle 22 will not .exceed 1%. In this manner, the :most complex diffractionpatternhaving very obscure fine lines can be readily scanned and the lines detected rela- I tivelyaeasilyvvith a fine degree of definition. An advantage accrues from the use of a relatively large: specimen such as shownin'Figure 2 forby the irradiation of a large-area amore intense line is reflected therefrom and focused on the focusing circle. 1

lhedetails of the construction of the detector found most useful for scanning the pattern are given in my .prior Patent No. 2,386,785. The detector comprises a Geiger Muller type of counter which is made specifically sensitive to the radiation being used to develop the pattern andcan berenderedsubstantially 100 per cent efficient in its, counting action.

Thapreparationof-the specimen. for irradiation is relatively simple. It is used in finely divided form, made into a thick paste. with water or a non-crystalline binding agent and coated evenly into the depression formed into the specimen mount. Binding agents such asmethyl cellulose, collodiom'styrene solutions, or polyvinyl alcohol are useful for the purpose. 5

Since certain changes in carrying outthe above method and in'the construction oi the apparatus described, which changes embody the invention,

can be made without departing from, the :scope of the, invention, it is intended that all :matter contained in the above description or shown in the accompanying drawings shallbe interpreted as illustrative and not in a limiting sense.

The invention described herein may :be manu- I factored and used by:or for the Governmentof the United States of America for governmental purposes without the payment of any royalties,

thereon or therefor.

Having described my invention, what I claimas new and desire to secure by Letters Patent of the United States is;

v1. The method .of developing an X-ray dif-.

fraction pattern of a substance comprising, coa'- ing an .arcuate mount-with a sample of the substance, defining an element of the arcuate sur-- face of said-mount as an axisof rotation for said mount, irradiating the material coated on. said.

mount with X-rays, detecting diffracted rays at a focal point on a focusing circle defined by the source of the X-rays, the axis of rotation of the specimen, and the focal point of the diffracted beam being measured, and during rotation ofthe mount maintaining the focal points of diffracted beams being measured substantially on a, common are by substituting different arcuate mounts having diiferent curvatures on which the material being examined is coated.

2. The method of developinganX-ray diffraction pattern of a substance comprising, irradiat ing the concave surface of a specimen thereof which is a section of acylinder to produce a beam of radiation, rotating said specimen through substantially about an axis forming an element of said cylindrical irradiated surface to develop. a diffraction pattern thereof, synchronously moving with said specimen a detector :to detect the focused diffracted beam corresponding to the anple of the material, irradiating the surface of said material with a divergent beam of x rays from a point source, detecting the focused diffracted rayson an arc of a focusing circle defined.- by the source of the rays, the axis of rotation of the specimen, and'the focal pointof .said diffracted beam,.and maintaining the locus of the focal points of the diffracted beams substantially along an are by substituting coated :mounts of different curvature for the different angular" positions. 4. The method of developing an X-ray diffraction pattern of a material comprising, irradiating a specimen thereof havinga surface curvatureformed to produce a focused diffracted beam of radiation at an angle corresponding to the angle of the irradiating beam, rotating said specimensubstantially 90 about an axis lying in its focusing surface to develop a diffraction pattern thereof, synchronously moving with said speci- :men a detector to detect the focused diffractedbeams along an are having as its center the'axis of rotation of the specimen, and substituting specimens of the same material but of different curvature to maintain the locus of the focal points-of the focused diffracted beam substan 9 tially concentric with the arc traversed by the detector.

5. In an X-ray spectrometer for developing X-ray diffraction patterns of materials by rotating an arcuate specimen of a material through an angle about an axis to maintain the focal point of the difiracted beam of X-rays on an arc of a circle having as its center the axis of rotation of the specimen, apparatus for maintaining the specimen in focusing relation to the incident radiation and allowing for change of its radius of curvature to correspond to different degrees of rotation thereof comprising, a holder to receive the arcuate specimen and to define a chord of the focusing circle, means for holding the arcuate specimen in fixed position in said holder, and means for adjusting the horizontal position of the arcuate specimen holder to make the axis of rotation of the holder lie in the surface of the specimen.

6. Apparatus for the development of an X-ray difiraction pattern of specimens, comprising, a fixed point source of X-ray radiation, a detector 10 of diffracted radiation movable along a fixed curved track, fixed holding means for said specimens disposed substantially in the plane of said source and said fixed track, and a series of specimens with their surfaces curved in one dimension and with varying radii of curvature, the curvature of a particular member of said series when said member is disposed in said holder defining an arc of a circle on which lie said point source of radiation and said detector, the particular position of said detector on its track correspondingto the curvature of said particular member.

HERBERT FRIEDMAN.

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

UNITED STATES PATENTS Number Name Date 1,589,833 Behenken June 22, 1926 2,377,862 Bond June 12, 1945