US3486021A - Goniometer for x-ray diffraction apparatus - Google Patents

Description

Dec. 23, 1969 $E|Go HONME ET AL 3,486,021

GONIOMETER FOR X-RAY DIFFRACTION APPARATUS Filed Nov. 14, 1967 2 Sheets-Sheet 1 Fl 6 23 5 I31! "a J 1 ii 1 llllll I, 20 g 18 Il INVENTORS. Se/g0 Honme Ga/ruo Kamafsubara UM M m l- M THE/R ATTORNEYS Dec. 23, 1969 ago, HONME ETAL 3,486,021

GONIOMETER FOR X-RAY DIFFRACTION APPARATUS Filed Nov. 14, 1967 2 Sheets-Sheet 2 INVENTORS.

Se/go Honme Ga/ruo By Kamafsubara v SM/5%,Mk in! THE/R ATTORNEYS United States Patent 3,486,021 GONIOMETER FOR X-RAY DIFFRACTION APPARATUS Seigo Honrne and Galmo Kornatsubara, Tokyo, Japan, assignors to Nihon Denshi Kabushiki Kaisha, Tokyo, Japan, a corporation of Japan Continuation-impart of application Ser. No. 628,382, Apr. 4, 1967. This application Nov. 14, 1967, Ser. No. 682,949 Claims priority, application Japan, Apr. 6, 1966, 41/ 21,666 Int. Cl. Gtlln 23/20 US. Cl. 256-515 7 Claims ABSTRACT OF THE DISCLOSURE A goniometer having a curved guideway pivotally mounted upon two collars that are movable along transverse lines, at the intersection of which is located a specimen to be analyzed. One of the collars has a crystal pivotally mounted thereon to diffract X-rays emanating from an electron beam bombarded specimen. The diffracted X-rays are detected by a detector mounted on the curved guideway. The relationship between the specimen, crystal, and detector, during the scanning of the diffraction spectra, is maintained by a constant length cable.

This application is a continuation-in-part of our copending application entitled Goniometer for X-Ray Diffraction Apparatus, Ser. No. 628,382, filed Apr. 4, 1967, and now abandoned.

Our invention relates to an X-ray diffractometer and more particularly to an improved spectrometric apparatus for the analysis of fluorescent X-rays emitted by a specimen when excited by the impingement of an electron beam thereon.

With X-ray analyzing apparatus, analysis is carried out by bombarding the surface of a specimen With an electron beam or an X-ray beam so as to cause the emission of X-rays therefrom, and then determining the nature of the specimen by analyzing the emitted X-rays. The analysis of the X-rays is carried out by impinging the emitted X-rays upon a crystal so that they are reflected onto an X-ray sensitive detector.

In order to accomplish the analysis it is necessary to maintain the focal relationship between the specimen, the crystal, and the detector throughout the entire scanning operation so that the X-rays are focused upon the detector. It is also necessary to alter the angularity of the crystal with respect to the specimen and to simultaneously adjust the detector with respect to the crystal such that the detector is at every instance, in the path of the diffraction X-rays.

With goniometers currently used in X-ray diffraction apparatus, especially in electron probe X-ray microanalyzers or X-ray fluorescent analysis apparatus, a diffraction crystal is mounted on one rotary arm and a detector on another rotary arm. These two arms are pivotally interconnected at their apexes at the center of the focal circle and are so adjusted through a set of gears that the angular movement of a second arm carrying the detector is double that of a first arm carrying the crystal, so that the X-rays will ultimately impinge upon the detector.

It is not, however, convenient to use this type of goniometer with electron probe X-ray microanalyzers since a large slit with a large apparatus, which enables X-rays irradiating from the specimen at different angles to impinge upon the curved crystal, must be. installed in a small specimen chamber When the detector is moved towards the crystal to scan spectrum forming X-rays diffracted at the crystal.

In another type of goniometer, a straight guideway or a slideway, arranged in the path of the X-rays, which emanate from the specimen is utilized in order to scan diffracted X-rays through the aperture of the slit at a constant angle with respect to the specimen. In this arrangement, a crystal moves along the guideway towards and away from the stationary specimen, and the angularities of the crystal with respect to the specimen and the scanning detector with respect to the crystal, for maintaining the diffracted X-rays focused upon the detector, are adjusted by the combination of the guideway and some linkages pivotally connected at the center of the focal circle. However, the mechanical arrangement utilized therein is or a very complex character.

Our invention provides a goniometer adapted for use in electron probe X-ray microanalyzer and similar devices that eliminates the above mentioned disadvantages. The invention provides a mechanical arrangement for producing circular motion about an intangible center which is especially adapted for use in X-ray diffraction apparatus. Furthermore, the invention provides a mechanical motion, especially adapted for use in a curved crystal type X-ray diffraction apparatus, to maintain the focal relationship between the specimen, the curved diffraction crystal, and the detector throughout the entire scanning operation. The invention also provides a mechanical motion of the type that causes the focal circle to roll around a stationary specimen, under examination, as a center, while the curved diffraction crystal travels along a straight line path relative to the specimen.

Generally, the invention provides a mechanical arrangement having a fixed Station for receiving the specimen to be examined; a curved path for transferring an X-ray detector along the focal circle; a supporting plate for securing the curved path together With a diffraction crystal thereon; a screw and a shaft angularly offset relative to each other for transferring the opposite ends of the supporting plate along a pair of lines which intersect at the specimen to be examined; a constant length cable mechanism for controlling the travel of the detector towards and away from the crystal, thereby keeping the crystal and the detector at all times in an appropriate fixed focus relation with respect to the specimen; and a spring for biasing the detector away from the crystal so as to orient the detector, at every instance, in the path of the diffracted X-rays.

In the accompanying drawings, we have shown preferred embodiments of our invention in which:

FIGURE 1 is a front elevation of our invention in which the condenser lens and window are sectioned;

FIGURE 2 is a perspective view of the constant length cable mechanism;

FIGURE 3 is a front elevation of a modification of the invention shown in FIGURE 1; and

FIGURE 4 is a diagrammatic view of an X-ray monochromator of the curved crystal type illustrating the paths of the crystal and the detector relative to the specimen.

Referring to FIGURE 1, a test specimen 1 is shown under a condenser lens 2 in an electron probe X-ray microanalyzer. Straight line AA' along which the center of the curved crystal 3 travels is defined by shaft or guide member 4 mounted on base 5. An internally threaded nut or collar 6 moves along the shaft or guide member on screw threads 7, and threaded holder 8, to which a second pulley 9 is pivotally connected, is slidingly received on the outer end of the shaft or guide member 4. The threaded holder 8 is fixed to base 5 by an appropriate means during the operation of the monochromator. Shaft or guide member 10 is mounted on base 5 along line B-B' which is offset at a angle relative to the line A-A, and a collar 11 is arranged so as to slide along shaft or guide member 10. Supporting plate 12 carries and supports curved or arcuate guideway 13. Plate 12 is pivotally mounted on both nut or collar 6 by a pivot pin (not shown) and collar 11 by pivot pin 15. The arcuate guideway 13, the diameter of which is equal to the diameter of the focal circle 16, is secured to plate 12 in coaxial relationship with respect to the focal circle relative to the center (not shown) thereof. Curved crystal 3 is fixed at the end of the pin 14. Pin 14 is secured to the center of disc 24 that is of the same size as pulley 17 and which is secured to plate 12 and is between plate 12 and pulley 17. Crystal 3 will, therefore, rotate with plate 12 and will be coincident with the focal circle. A U-shaped collar 18 is arranged so as to move along the arcuate guideway 13 and mount 19 pivotally mounted on U-shaped collar 18. A third pulley 20 is rotatably arranged on the mount 19 and an X-ray detector 21 is also oriented thereon so as to be positioned on the focal circle at all times.

In scanning the diffraction spectrum, the spacing between the crystal and the detector must be varied. This spacing is accomplished by constant length cable 22, which is so arranged as to control the travel of the detector towards and away from the crystal along the curved or arcuate guideway 13.

As shown in FIGURE 2, flight 23 of the constant length cable 22, the end of which is fixed to disc 24 at F is trained around the second pulley 9 and extends therefrom to the first pulley 17. The opposite flight 25 of the cable, the end of which is fixed to disc 24 at F (see FIGURE 1) and is trained around the third pulley 20 and extends therefrom to the first pulley 17. The bight portion 26 of the cable passes around the first pulley 17 which is rotatably mounted on the upper end of the plate 12 by means of pin 14 secured to disc 24. The constant length cable mechanism used in our invention is arranged to avoid chafling between the two flights, thus ensuring that X-ray detector 21 moves along the curved guideway smoothly.

When the curved crystal is brought close to the specimen, supporting plate 12 and disc 24 simultaneously rotate about the center of focal circle 16. Variations due to changes in the amount of cable taken up by pulley 17 are exactly compensated by the equal but opposite changes in the amount of cable taken up by disc 24. It is, therefore, possible to exactly maintain the distance between the crystal and detector equal to the distance between the crystal and specimen.

Furthermore, in order to keep the diffracted spectrum focused upon the detector, the detector must be oriented at all times in the focused position with respect to the diffracted X-rays which emanate from the crystal. For this purpose, spring 27 is provided, one end of which is anchored to base 5, the other end being connected to wire 28. The other end of the wire is fixed to collar 18 so as to bias the detector away from the crystal.

Additionally, in order to minimize stretch on spring 27, a wheel 29 is pivotally mounted on base 5 adjacent to the inner end of screw 7, a second wheel 30 is also pivoted on supporting plate 12 adjacent to the crystal, and a third wheel 31 is mounted for pivotal movement on supporting plate 12 adjacent to collar 11. One flight of the wire 28 is trained around wheel 29 and extends therefrom to second wheel 30. The other flight, the end of which is anchored to U-shaped collar 18, is stretched around third wheel 31 and extends therefrom to the second wheel 30. The bight of the wire is passed over the second wheel 30. As a consequence, spring stretch is reduced to a minimum even when the detector 21 is brought close to the crystal, due to the fact that the second pulley 30 is moved towards specimen 1 along screw 7 together with the supporting plate.

Referring to FIGURE 3, we have shown another embodiment of the apparatus according to our invention. The screw 57 and the shaft or guide member 50 are, in this case, arranged parallel to line X-X' and line Y-Y', respectively. Curved or arcuate guideway 63, having a smaller diameter than focal circle 66, is oriented on supporting plate 52 in coaxial relationship to focal circle 66 relative to the center thereof. Pin 64, to which crystal 53 is fixed, is arranged to move along line X-X' when nut or collar 56 moves along screw 57. Pivot pin 65, on which support plate 52 is pivotally connected to collar 51, is arranged to move along line Y-Y. X-ray detector 61 is arranged so as to move along the circumference of the focal circle 66 throughout the scanning movement of the detector. Second pulley 59 is, in this case, pivoted to base 55 at a point generally in line with the path of travel of crystal 53 and spaced beyond the extreme limit of travel of the crystal away from the specimen.

In operation, an electron beam designated by BB, in FIGURE 1, is first emitted from an electron gun (not shown) and focused on the specimen surface by condenser lens 2. X-rays then diverge radially, some of which pass through a window 32 at an angle or with respect to the specimen.

The X-rays strike the curved crystal at an incident angle 6, and assuming their wave lengths fulfill the Bragg equation, they are deflected by the crystal so as to focus on detector 21. Subsequently, screw 7 is rotated by means of handle 40 to scan the spectrum.

The center position of the crystal then changes from its original position C to other positions, e.g., C C along line A-A' as shown in FIGURE 4. Angularity of the crystal with respect to the specimen is simultaneously altered in response to rotation of curved guideway 13. At the same time, the travel of the detector 21 toward and away from crystal 3 is accomplished by the constant length cable mechanism. The center position D of the detector is made to follow the focal circle in such a way that the distance between the crystal and the detector D C D -C is kept equal to the distance between the specimen and the crystal, as designated by C -Z, C -Z. Since the center of the detector is arranged so as to move along the focal circle, the tension spring 27 together with the cable 22 adjusts the detector inclination with respect to the crystal, thus maintaining the detector at all times in the path of the crystals diffracted rays while scanning the diffracted X-rays. In accordance with the travel of the detector towards the crystal, the inclination of the crystal is altered so as to change incident angle 0 to 0 0 As heretofore described, the constant length cable together with the biasing means operates to maintain the proper focal relationship between the specimen, the detector, and the crystal. The inclination of the detector with respect to the crystal is also altered in accordance with the change in the angularity of the crystal, thus causing the diffracted X-rays to focus on the detector.

The goniometer described in our invention adapted for use in the electron probe X-ray microanalyzer or X-ray fluorescent analysis apparatus is thus seen to be relatively simple and compact. It is also inexpensive to manufacture, since the use of expensive cams and gears for controlling the relative motions of the mechanism has been eliminated. Additionally, it is possible to reduce the focal circle itself as the mechanical arrangement has no rotary arms or linkages pivotally connected at the center of the circle, thus enabling the analysis of fluorescent X-rays with high density, by bringing the crystal very close to the specimen.

While we have shown and described preferred embodiments of our invention, it may otherwise be embodied within the scope of the appended claims.

We claim:

1. A goniometer for X-ray diffraction apparatus comprising:

(A) a base;

(B) first and second linear guide members mounted on said base and angularly offset relative to each other and lying on respective lines that meet at an apex;

(C) first and second collars, said first collar being moveably mounted on said first linear guide memher and said second collar being moveably mounted on said second linear guide member;

(D) an arcuate guideway pivotally mounted on said first and second collars, and lying on a circle that passes through said apex;

(E) a curved crystal pivotally mounted on said first collar and having a surface circumferentially positioned on said circle passing through said apex;

(F) an X-ray detector moveably mounted on said arcuate guideway;

(G) means for moving said first collar along said first guide member; and

(H) means for moving said detector simultaneously with the movement of said first collar to continuously orient said detector and said crystal and to maintain the distance between the crystal and the detector equal to the distance between the crystal and said apex.

2. A goniometer as set forth in claim 1 wherein said means for moving said detector simultaneously with the movement of said first collar comprises:

(A) a holder mounted adjacent the end of said first guide member opposite said apex and having a first pulley mounted thereon;

(B) a disc rigidly mounted on said guideway at said first collar;

(C) a second pulley pivotally mounted upon said disc;

(D) a third pulley mounted on said moveable detector;

and

(E) a cable secured at one of its ends to said disc, said cable being passed around the pulley mounted on said holder and thereafter trained around said second pulley and then passed around said third pulley, the other end of said cable passing over the first end and being attached to said disc to thereby maintain the distance between the crystal and detector and the crystal and said apex equal when said first collar is moved along said first guide member.

3. A goniometer as claimed in claim 2 wherein said first guide member is threaded and said first collar is internally threaded so that rotation of said guide member causes said first collar to move along said guide member.

4. A goniometer as claimed in claim 2 including a support plate pivotally mounted on said first and second collars, said arcuate guideway being mounted on said plate; a spring biasing means for biasing said detector away from said crystal comprising:

(A) a spring having one end attached to said base and substantially subtending said arcuate guideway;

(B) a first wheel mounted on said base and second and third wheels mounted on said plate, said first and second wheels being on a line substantially parallel to said first guide member, said second and third wheels being on a line substantially parallel to said spring; and

(C) a cable secured at one of its ends to the other end of said spring and passing around said first, second and third wheels and secured at its other end to said detector.

5. A goniometer as claimed in claim 1 wherein said lines on which said guide members are located form an included angle of 70.

6. A goniometer as claimed in claim 1 wherein said circle passing through said apex and on which said arcuate guideway is located has a diameter equal to the diameter of the focal circle of the X-ray diffraction apparatus.

7. A goniometer for X-ray diffraction apparatus comprising:

(A) a base;

(B) first and second linear guide members mounted on said base and angularly offset relative to each other, said guide members lying parallel to lines that lie on said base and meet at an apex;

(C) first and second collars, said first collar being moveably mounted on said first linear guide member, and said second collar being moveably mounted on said second linear guide member;

(D) an arcuate guideway pivotally mounted on said first and second collars and lying on a circle concentric to a circle passing through said apex;

(E) a curved crystal pivotally mounted on said first collar and having a surface circumferentially positioned on said circle passing through said apex;

(F) an X-ray detector moveably mounted on said arcuate guideway and lying on said circle passing through said apex;

(G) means for moving said first collar along said first guide member; and

(H) means for moving said detector simultaneously with the movement of said first collar to continuously orient said detector and said crystal and to maintain the distance between the crystal and the detector equal to the distance between the crystal and the apex.

References Cited UNITED STATES PATENTS 3,099,743 7/1963 Ichinokawa 2505l.5 3,107,297 10/1963 Wittry 25051.5

RALPH G. NILSON, Primary Examiner A. L. BIRCH, Assistant Examiner U.S. Cl. X.R.

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