US3394255A - Diffraction mechanism in which a monochromator diffracts the X-ray beam in planes transverse to an axis of specimen rotation - Google Patents

Description

y 1968 T. c. FURNAS. JR 3,394,

HANI SM IN WHICH X-RAY DIFFRACTION MEC MONO X TOR DIFFRACTS THE X-RAY AM IN PLA TR VER AN A OF SPECIM ROTATION Filed June 28, 1965 5 Sheets-Sheet l INVENTOR. THOMAS C. FURNAS JR.

ATTORNEYS.

July 23, 1968 T c. FURNAS. JR 3,394,255

X-RAY DIFFRACTION MECHANISM IN WHICH A MONOCHROMATOR DIFFRACTS THE X-RAY BEAM IN PLANES TRANSVERSE TO AN AXIS OF SPECIMEN ROTATION Filed June 28, 1965 5 Sheets-$heet 2 Fig. 3

INVENTOR. THOMAS C. FURNAS JR.

ATTORNEYS July 23, 1968 T. c. FURNAS. JR 3,394,

X-RAY DIF'FRACTION MECHANISM IN WHICH A MONOCHROMATOR DIFFRACTS THE X-RAY BEAM IN PLANES TRANSVERSE TO AN AXIS OF SPECIMEN ROTATION Filed June 28, 1965 3 Sheets-Sheet 5 L ms T w M willl m HI #r D T I L IIIIRRHW r| J KW. llll Ill DI ll UK r h WIILIIWL L 5 1 4 3 5% wk 1 2 |1 L MN z Q II I w w w w HM nun u-u-uu------- INVENTOR THOMAS C. FURNAS JR.

ATTORNEYS United States Patent 3,394,255 DIFFRACTIQN MECHANISM IN WHICH A MONO- CHROMATOR DIFFJRACTS THE X-RAY BEAM 1N PLANES TRANSVERSE TO AN AXIS OF SPECIMEN ROTATION Thomas C. Furnas, Jr., Cleveland Heights, Ohio, assignor, by mesne assignments, to Picker Corporation, White Plains, N.Y., a corporation of New York Filed June 28, 1965, Ser. No. 467,214 19 Claims. (Cl. 250-515) ABSTRACT OF THE DISCLOSURE An X-ray diffraction mechanism in which a monochromator diffraction X-ray beam is utilized. Each characteristic X-ray wavelength is diffracted a different and characteristic amount than other wavelengths such that the beam is separated into planes of radiation each of one characteristic wavelength. The planes are transverse to an axis of specimen rotation. The disclosure also includes a method of conducting X-ray diffraction studies with the X-ray planes so diffracted.

This invention relates to X-ray diffraction and more particularly to a novel and improved process and apparatus utilizing monochromator crystals for conducting X- ray diffraction studies.

In X-ray diffraction, it is customary to position a specimen for rotation about an axis known as the theta or the omega axis, and to rotate the specimen through an angle known alternately as theta or omega. As the specimen is rotated, it is irradiated with a beam of X-rays which is diffracted by the specimen. Customarily as the specimen is rotated through an angle theta the rays diffracted by the specimen are detected and then suitably recorded.

The primary beam emitted by an X-ray tube is a mixture of X-rays of various wave lengths. In the past some studies have been conducted in which the primary beam is directed against a monochromator crystal (or ruled grating) which monochromator diffracts the primary beam toward and thereby irradiates the specimen. As the primary beam is diffracted from the monochromator, each wave length is diffracted in a different direction so that the X- rays from the monochromator which strike the specimen (because it is small) are of substantially a single wave length.

In the past where monochromators have been used to provide a virtual source of monochromatic X-rays, the monochromator has been positioned so that X-rays have been ditiracted in planes which are parallel to the theta axis. The dispersion of X-rays of various wave lengths resulting from the monochromator diffraction is known as spectral dispersion. In these prior arrangements the spectral dispersion has been perpendicular to the theta axis and, therefore, in the plane of rotation about the theta axis. Similary, the so-called plane of diffraction of the monochromator has been perpendiuclar to the theta axis. While this arrangement has provided beams essentially of the desired and appropriately defined wave length spread for irradiating the specimen for many diffraction experiments, it has many shortcomings when used in other diffraction experiments. This is particularly true with those experiments concerned with the collection of sets of integrated intensities for the purpose of crystal structure determination, and those concerned with powder diffrac tometry. These shortcomings include at least the followmg:

(1) It must be recognized that the specimen itself is a "ice crystal. When the specimen is parallel to the monochromator, the dispersions of rays diffracted by the two crystals are opposite and offset one another. When the specimen is anti-parallel; the dispersions are additive. For this reason there is an asymmetry of geometry and type of diffraction for reflections from the specimen which occur as the specimen is rotated clockwise or counterclockwise about the theta axis from a given position between the parallel and anti-parallel positions. This asymmetry is so important that it is recognized by special names which describe the parallel (1, 1) and the anti-parallel (1,1) reflecting positions.

(2) There is an error (often indeterminant) in the integrated intensity measurement due to the fact that the radiation from the monochromator is directed and not diffuse. Thus, the radition is dispersed spatially by wave length and unable to irradiate all parts of the specimen uniformly and identically in wave length and intensity. This error is magnified by its simultaneous occurrence with the asymmetry mentioned above.

(3) There is a general inability for extreme inconvenience to change the angular divergence of X-rays striking the specimen from the primary source as seen in virtual image through the monochromator. It is diflicult or impossible to accommodate the very different geometries desired for (a) searching for reflection from the specimen; (b) stationary intensity measurements; (c) scanning intensity measures; and, (d) determination of lattice parameters and mosaic spread. These too are aggravated bv the asymmetry described above.

(4) A closely related problem is that it is extremely diffcult to align the X-ray tube, the monochromat-or, the specimen, and the detector. This is true because the asymmetry described above makes the reflection very narrow. It is also true because true optimum positioning requires a multitude of scans since it is practically impossible to get all of the specimen to diffract at once.

-(5) Some studies are made in a plus two-theta region; i.e., clockwise from a plane located by the theta axis and the source of X-rays exciting the specimen. Other studies are made in a region which is counterclockwise from this plane and known as minus two-theta, There is considerable uncertainty and error both in the interpretation of the data that might be collected and in accounting for the unequal scan ranges involved in the measurement and comparison of the plus two-theta reflections and minus two-theta reflections because of the asymmetry mentioned above. Although no designation has been officially specified in the literature it will be convenient to refer to the parallel (1, 1) position as belonging to the positive two-theta region since this is the one most commonly employed. While there generally is negligible asyminetry to a direct X-ray source this terminology agrees with the general assertion that the positive two-theta region is that permitting the largest two-theta range and this usually places the X-ray tube anode surface and the specimen diffracting planes in the parallel configuration to one another.

(6) The dispersion calculation and corrections are different in the positive and in the negative two-theta regions due to the asymmetry mentioned above.

(7) In the past, the obtainment of higher intensity monochromatic X-irradiation of the specimen has been attempted or achieved by cylindrically curving the monochromator about an axis parallel to the theta (or omega) axis. When this is done, the angular range through which the specimen must be rotated to pass entirely through its reflecting position is increased. Although no special designation has been given in the literature, it appears appropriate to use (C, 1) for the curved parallel reflecting position and (0,1) for the curved anti-parallel reflecting position to emphasize that complications due to asymmetry still exist.

(8) In powder diifractometry it is necessary to use soller slits in the X-ray beam between the monochromator and the specimen to limit the divergence along the theta axis. The vanes of the soller slit are perpendicular both to the theta axis and to the diffracting planes of the monochromator in the common arrangement described above.

Asymmetry is of considerable importance as is demonstrated by its presence in six of the above list of eight short-comings experienced with the commonly employed arrangement. Accordingly, it should be considered in further detail.

In the parallel (1, -1) position the clilfracting planes of the monochromator are parallel to the ditfracting planes of the specimen. (Actually 6 0 where O is the diffraction angle at the monochromator and a the diffraction angle at the specimen.) Strict parallelism is achieved when the diffraction angles of the crystal and monochromator are equal. When this is true then all the wave lengths diffracted from the monochromator are simultaneously diffracted from the specimen. Thus, the spectrum dispersed by the monochromator is recombined by reflection from specimen planes in the parallel (1, position. The angular Width of the reflection measured by rotation of the specimen about two-theta or omega axis generally is called the instrument width as it somewhat characterizes (a) the sizes of apertures; (b) the mosaicity of the monochromator and of the specimen; (c) the net angular convergence of X-rays upon the specimen; and, (d) the ability of the specimen to diffract X-rays.

In the position where the diffracting planes of the monochromator and specimen crystals are antiparallel, the planes are at 0 +0 When this is true then only one wave length at a time is diffracted from the specimen. Thus, the spectrum dispersed by the monochromator is further dispersed by reflection from specimen planes in the anti-parallel (1, 1) position.

In single crystal structure analysis it often is very important to be able to measure the intensities of reflection in certain positions in the plus two-theta region and compare them with the corresponding intensities of reflection measured in the minus two-theta region. These are related to one another as are the front and back of a mirror. A very convenient means for making these measurements is to make one clockwise and the other counterclockwise about the theta axis. These are, therefore, precisely the parallel and anti-parallel positions mentioned earlier so the importance of any anomalies, differences or asymmetry of the measurements becomes greatly magnified. These measurements are commonly referred to as being made in the positive or plus two-theta region and in the negative or minus two-theta region.

With the present invention, these shortcomings and anomalies are overcome by providing a construction wherein the dispersion from the monochromator is specifically parallel to the omega, theta axis of rotation of the specimen. Thus, each Wave length of X-ray energy is in a plane which is transverse to the omega, theta axis. Because of this resultant spectra are obtained at both plus and minus two-theta which are equal and opposite. Although it is preferable that the dispersion of the specimen be perpendicular to the omega, theta axis of specimen rotation (the socalled equatorial diffraction geometry), the general advantages of the present invention are equally obtained in the Weissenberg or upper lever diffraction geometries. In particular, the Lorentz, polarization and dispersion correction for a particular reflection whether it is observed in the positive or negative twotheta region are the same. In stationary specimen intensity measurement techniques this invention is also beneficial. This is true because the specimen will diffract in a manner which permits many stationary studies to be 4 conducted where in the past specimen rotation has been required.

As noted above, with this invention, the spectral dispersion of the monochromator is parallel to the omega, theta axis and, therefore, perpendicular to the plane of rotation about the coincident omega, theta axis. To distinguish this arrangement from the one used in the past and to emphasize its symmetrical character the terminology plane perpendicular (l, P) is proposed to describe the use of a plane grating, plane reflection crystal or a plane transmission crystal as the monochromator oriented with its dispersion perpendicular to the specimen rotation axis or specimen dispersion. The terminology curved perpendicular (C, P) is proposed to describe the use of a curved grating, curved reflection crystal or curved transmission crystal as the monochromator oriented with its dispersion perpendicular to the specimen rotation axis or specimen dispersion.

With this invention, the primary source of X-radiation is positioned to one side of the monochromator away from the specimen. The primary source is above or below the monochromator when the omega, theta axis is vertical. The rays are directed at the monochromator at an angle such that a diffracted beam of a selected wave length is directed to the specimen.

In addition to the advantages of overcoming all of the above-listed problems, a construction of the improved type has the effect of allowing the divergence of X-rays irradiating the specimen to be changed readily by changing the take-off angle to the X-ray tube target. This can be done without effecting the monochromaticity of the beam striking the specimen.

Another advantage of this arrangement where a line rather than a spot source is used, it is possible to eliminate the soller slit assembly between the X-ray source and the specimen without disturbing the focusing properties useful in the plane of diffraction or measurement. This is especially true where the specimen is a powder. Either a soller slit or a second (1, P) monochromator arrangement can be used between the specimen and the detector. In this case it is desirable that the two monochromators bear a parallel (l, -l) relationship to one another.

Accordingly, the objects of the invention are to provide a novel and improved difiractometer utilizing a monochromator and a method of conducting diffraction studies.

Other objects and a fuller understanding of the invention may be had by referring to the following description and claims taken in conjunction with the accompanying drawings in which:

In the drawings:

FIGURE 1 is a perspective view of a diffractometcr made in accordance with this invention;

FIGURE 2 is an elevational view, on an enlarged scale with respect to FIGURE 1, of the novel tube and monochromator crystal support mechanism of this invention with parts broken away and removed;

FIGURE 3 is an end elevational view of the device and scale of FIGURE 2, as seen from the plane indicated by the line 33 of FIGURE 2, and with parts broken away and removed;

FIGURE 4 is a top plan view of the structure and scale of FIGURE 2;

FIGURE 5 is an end elevational view of the structure and scale of FIGURE 2 as seen from the plane indicated by the line 5-5 of FIGURE 2; and,

FIGURE 6 is a sectional view, on an enlarged scale With respect to FIGURE 2, of the crystal support, as seen from the plane indicated by the line 66 of FIG- URE 2.

In FIGURE 1, a diffractometer is shown generally at 10. The diffractometer It is preferably of the type described and claimed in copending application Ser. No. 236,468, filed Nov. 2, 1962, which is now United States Patent 3,218,458 issued Nov. 16, 196 5, T. C. Furnas, Jr. and entitled Diffractometer. The diffractometer includes a housing 11. A two-theta member 12 is journaled in the housing 11 for rotation about a theta axis. Assuming the housing 11 is horizontal, the theta axis is a vertical axis which intersects the specimen, as will become more apparent from the subsequent description.

A two-theta arm 13 is secured to the two theta member 12. The two-theta arm 13 supports the usual detector 15 and slit structure 16. A cone-like collimator structure 17 is also secured to the two-theta arm 13 for collimating rays diffracted by a specimen before they pass through the slit 16 into a detector 15.

A goniometer is shown generally at 20. The goniometer pictured is one of the type described and claimed in detail in US. Patent 3,189,741 issued June 15, 1965 to George V. Patser under the title Goniostat. The goniostat 20 is mounted on a theta member 21 for rotation about the omega, theta axes.

The goniostat 20 includes a phi head 22 which supports a'specimen S at a position along the omega, theta axes. The specimen S is also located on a chi axis which is the horizontal axis of the goniostat 20 when the housingll is horizontal. The phi head 22 is orbital about the chi axis and equipped to selectively rotate the specimen S about a phi axis. As is indicated by the preceding discussion, the chi axis is perpendicular to and intersects the omega, theta axes at the point where the specimen is rotated. Similarly, the phi axis intersects these axes at the same point and is also perpendicular to the chi axis. A phi axis may'be any radius of the goniostat perpendicular to the chi axis. An eye piece 23 is secured to the goniostat 20 and positioned for use in locating the specimen S precisely at the intersection of these axes.

A pair of X-ray tube support pedestals 25, 26 are fixed to the housing 11. An X-ray tube and monochromator assembly is shown generally at 30. The assembly 30 is secured to the pedestals 25, 26 as by bolts 31. The assembly 30 will be best understood by reference to FIGURES 2-6.

The assembly 30 includes a base 32 which is the element of the assembly that is fixed to the pedestals 25, 26 by the bolts 31. The base 32 includes an upstanding arm 33 which is at the right hand end of the base as viewed in FIGURE 2. The upstanding arm 33 extends longitudinally of the base 32 and provides a support for monochromator and X-ray tube pivots as will become apparent presently. The base includes a second upstanding arm 34 which is at the left hand end of the base as viewed in FIGURE 2. The second upstanding arm 34 is transverse with respect to the base 32 and supports the mechanism for causing adjustment pivoting the X-ray tube about a crystal axis as will also become more apparent presently.

A rigid pivot support arm 35 is secured to the base arm 33 extending upward from the base and outward toward the goniostat 20. A stepped crystal and tube Support shaft is provided at 37. The crystal and tube support shaft 37 is rotatably supported in the pivot arm 35 by small and large bearings 38, 40. A Washer 41 is clamped against one race of the small bearing 38 by a nut 42 Which threads on one end of the shaft 37. The support shaft,37 includes an enlarged part 43 which engages a race of the large bearing so that the bearings 3840 serve not only to journal the support shaft 37 but also as thrust bearings to locate it axially.

An X-ray tube support member 45 is provided. The support member 45 extends longitudinally with respect to the base 32. The support member 45 includes an upstanding pivot arm 46 at its right hand end as seen in FIGURE 2. The pivot arm 46 is journaled by a bearing 47 on an end portion 48 of the support shaft 37. The end portion 48 is at the right hand end as seen in FIG- URE 2. An examination of FIGURE 2 will show that the tube support base 45 is pivotal about the axis of the support shaft 37. The mechanism for adjusting the tube support base 45 about the axis of the support shaft 37 will be described below.

An X-ray tube housing 50 is shown in solid lines in FIGURES 1 and 3 and indicated in phantom in FIG- URES 2, 4, and 5. The X-ray tube housing 50 includes a focal spot end portion 51 of reduced size. The end portion 21 is square in cross section and houses the X-ray tube target. The target is indicated in dotted lines at 53 in FIGURE 2.

A spherical bearing support assembly is shown gen erally at 54. This sup-port assembly 54 secures the focal spot end portion 51 of the X-ray tube housing 50 to the X-ray tube base 45. The spherical bearing support assembly 54 is of the type described in detail in the above-referenced copending application for a diffractometer. As an examination of FIGURE 3 Will show, the spherical bearing shown in dotted lines at 55 is immediately below the focal spot of the target 53.

A knurled head 57 of a take-off angle adjustment screw is visible in FIGURES 1 and 2. A portion of the adjustment screw is visible at 58 in FIGURE 1. The take-off angle adjustment is of the type described in the abovereferenced patent application. The adjustment screw 58 threadably engages the X-ray tube housing 50 to shift it transversely with respect to the base 45 and adjust the take-off angle about the axis of the spherical bearing 55.

A pivot adjustment arm 60 extends upwardly from and forms one end of the X-ray tube support bracket '45. The pivot adjustment arm 60 is at the left hand end of the bracket 45 as viewed in FIGURES 2 and 4. An arcuately curved pivot control shoe 61 is secured to the upstanding arm 60 as by bolts 63. An arcuately curved lower surface 64 of the shoe 61 rides on a pair of rollers 65 secured to the base arm 34. A hold-down roller 66, FIG- URES 2 and 4, rides on an upper arcuate surface 67 of the shoe 61. The hold-down roller 66 is also secured to the arm 34. Coaction of the rollers 65, 66 with the shoe 31 causes any relative movement to be along an arcuate path.

A worm gear 70 is secured to the arm 60 and the shoe 61 by the bolts 63. A worm 71 engages the worm gear 70 such that rotation of the worm 71 will cause arcuate movement of the worm gear 70 and the connected mechanism. Thus, rotation of the worm 70' will cause rotation of the X-ray tube about the axis of the support shaft 37.

An odometer 72 is secured to the base 32 and connected to the worm 71 by a worm shaft 73. Rotation of odometer handles 74 will cause rotation of the shaft 73 and thus pivotal adjustment movement of the X-ray tube about the axis of the support shaft 37. The odometer is provided so that one can determine the amount of adjustment movement of the X-ray tube about the axis of the support shaft 37.

Referring now to FIGURES 2 and. 6 in particular, a semi-cylindrical segment 75 is cut out of the section 43 of the support shaft 37. A monochromator crystal 76 is positioned in a recess 77 in the section 43 so that the monochromator crystal is disposed with its reflecting surface along the axis of the support shaft 37, and immediately below the segment 75.

The segment 75 is closed by a primary beam arcuately curved clip 79 and a diffracted beam arcuately curved clip 80. It should be noted here that for clarity of illustration the clips 79, 80 are not visible in any of the figures other than FIGURE 6. The primary beam clip 79' has a pair of arcuate recesses 81 which receive the clip 80 and permit relative rotation of the two clips. The two clips overlap and surround the shaft portion 43 between the bearings 40, 47, so that the segment 75 is completely closed except for apertures 82, 83 in the clips 79, 80 respectively.

The X-ray tube is preferably equipped with shutters of the type described and claimed in detail in US. Patent No. 3,113,214, issued to T. C. Furnas, In, on Dec. 3, 1963, under the title of Ditfractometer Shutter. This shutter engages an insert 84 which defines the aperture 32 of the clip 81. Thus, the clip 84 and the shutter together define an X-ray pervious passage which collimates and conducts the primary X-ray beam from the target 53 of X-ray tube to the monochromator crystal 76. Rays diffracted by the monochromator crystal 76 pass through the aperture 83 0f the clip 8t) and into a collimating structure 85. These diffracted rays pass through the collimating structure 85 and are thence directed against the specimen S.

In alignment of the X-ray tube and the monochromator crystal, some adujstment of the crystal may be desired. Accordingly, a disc 90 is secured to the end of the support shaft 37 opposite the washer 41. An adjustment lever 91 is secured to the disc 9! A spring 92 acts against the lever 9'1 forcing it into engagement with an adjustment set screw 93. With this structure the angle of the planes of diffraction of the monochromator crystal '76 can be adjusted by rotation of the set screw 93.

Method of operation When the device is operated, a specimen S is first mounted on the phi member 22. The position of the specimen is adjusted until it is located on the cross hairs provided to the eye piece 23. Manual adjustment of the phi, chi, omega, theta, and two-theta angles about their respective axes can be accomplished in the manner taught in the above-referenced patent and application until the specimen is precisely positioned for a desired study.

The handle 74 of the odometer is rotated until the appropriate angle of the primary beam emanated by the X-ray tube to the plane of diffraction of the specimen crystal is obtained. The set screw 93 may be rotated to adjust the plane of the monochromator crystal to its desired attitude.

Once these various adjustments have been made, the X-ray tube is energized and the shutter opened. The specimen S will be struck by substantially a single wave length of X-rays throughout its study and the specimen will be rotated appropriate amounts about the several axes. While the specimen is being rotated, the detector will be selectively rotated about the two-theta axis and, as noted in the introduction, always in the plane of a given and selected wave length of X-rays, due to the novel positioning of the monochromator crystal. It will be apparent that all but substantially Onewave length of X-rays pass either above or below both the specimen and the detector so that the specimen and detector are acted on by substantially a single wave length.

Although the invention has been described in its preferred form with a certain degree of particularlity, it is understood that the present disclosure of the preferred 'form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may 'be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

What is claimed is:

1. In a mechanism utilizing X-ray energy for the nondestructive testing of a specimen, the combination of:

(a) a support 'for mounting a specimen along an axis;

(b) beam diffraction means mounted in spaced relationship with the support and positioned to ditfract X-ray energy divergent in planes transverse to said axis; (0) an X-ray source secured in spaced relationship with said diffraction means and positioned to direct a beam of X-rays against said diffraction means;

((1) said diffraction means being positioned to diffract portions of said beam toward a mounted specimen; and,

(e) a detector for measuring rays diffracted by a specimen and mounted for positioning in a plurality of positions in a plane transverse to said axis.

2. The device of claim 1 wherein the diffraction means is a monochromator crystal adjustable about an axis which is transverse and spaced from the previously mentioned axis and transverse to said beam.

3. The device of claim 2 wherein the X-ray source is adjustable about said crystal adjustment axis.

4. The device of claim 1 wherein the X-ray tube assembly is adjustable about an axis transverse to and spaced from said previously mentioned axis.

5. In an X-ray mechanism for the non-destructive testing of a specimen, the combination of:

(a) a housing;

(b) a rotatable omega member journaled in said housing and rotatable about an omega axis;

(c) specimen supporting means mounted on said omega member and including means to support a specimen at a location along said axis;

(d) a crystal mounted on said housing and positioned to diffract X-rays in planes transverse to said omega axis;

(e) an X-ray tube assembly including a focal spot mounted on said housing and positioned with said crystal between the focal spot and said location; and,

(f) said X-ray tube assembly including collimating means for delineating a beam of X-rays directed against said crystal whereby said crystal will diffract portions of said beam to said location.

6. The device of claim 5 wherein the tube assembly is mounted on the housing by a supporting structure which includes means to rotate the tube assembly about an axis intersecting the crystal.

7. The device of claim 5 wherein the crystal is mounted on the housing by supporting structure which includes means to rotate the crystal about an axis intersecting the crystal.

8. The device of claim 7 wherein said X-ray tube assembly is mounted on the housing by supporting structure including means to rotate the X-ray tube about said crystal adjustment axis.

9. The device of claim 8 wherein the tube assembly is also adjustable about an axis passing through said focal spot.

10. In a method of conducting an X-ray diffraction study, the improvement comprising:

(a) diffracting a source of X-ray energy to separate said energy into planes of energy of differing wave lengths;

(b) positioning an X-ray specimen in a plane of a selected wave length; and,

(c) rotating a detector means about an omega axis transverse to said plane and intersecting the specimen while so positioned.

11. The method of claim 10 including the step of adjusting a selected one of the X-ray source and crystal about an axis intersecting the crystal and transverse and spaced from the omega axis.

12. In combination:

(a) a diffractometer including theta and two-theta mechanisms rotatable about a common axis;

(b) a detector mounted on the two-theta mechanism;

(c) a goniostat mounted on the theta mechanism;

(d) a specimen support to mount a specimen on the goniostat;

(e) collimating structure on the two-theta mechanism between the specimen and the detector for collimating a beam of X-rays diffracted by the specimen;

(f) first and second pedestals mounted on the diffractometer (on the side of the goniostat opposite said detector);

(g) an X-ray tube and crystal assembly mounted on the pedestals and positioned to irradiate a specimen on the goniostat, said assembly comprising:

(i) a base member with first and second spaced upstanding arms;

(ii) a monochromator and X-ray tube pivot support shaft journaled on the first arm;

(iii) an X-ray tube support journaled on said pivot support shaft;

(iv) an X-ray tube on said tube support;

(v) X-ray tube rotation adjustment means mounted on the second upstanding arm and connected to the tube;

(vi) take-off angle adjustment means between said X-ray tube and said base member;

(vii) said pivot support shaft including a cutaway segmental portion defining a crystal opening; and,

(viii) a monochromator crystal mounted in said opening in the path of a beam emanated by said X-ray tube; and,

(b) means to collimate X-rays diffracted by said monochromator crystal and direct the collimated beam against the specimen.

13. In combination:

(a) a diffractometer including theta and two-theta mechanisms rotatable about a common axis;

(b) a detector mounted on the two-theta mechanism;

(c) a specimen support to mount a specimen on the theta mechanism; and,

(d) an X-ray tube and crystal assembly mounted on the diffractometer and positioned to irradiate a specimen on the support, said assembly comprising:

(i) a base member;

(ii) a monochromator and an X-ray tube pivot support shaft journaled on the base member;

(iii) an X-ray tube support journaled on said pivot support shaft;

(iv) an X-ray tube and housing on said tube sup- (v) X ray tube rotation adjustment means mounted on the base member and connected to the tube;

(vi) said pivot shaft including a cutaway portion defining an opening; and,

(vii) an X-ray diffraction means mounted in said opening in the path of a beam emanated by said X-ray tube and positioned to diffract X-rays toward said specimen.

14. The device of claim 13 wherein first and second arcuately curved clips overlie one another and are mounted on said shaft support to close the perimeter of said opening, said clips respectively including a primary beam aperture in communication with an opening in the X-ray tube housing and a diffracted beam aperture positioned to conduct X-rays diffracted by said diffraction means toward said specimen.

15. The device of claim 13 wherein said X-ray tube adjustment means includes a worm gear and a worm.

16. The device of claim 15 wherein an odometer is connected to the worm.

17. The device of claim 13 wherein a means for adjusting the diffraction means about the aixs of the support shaft is provided.

18. In a method of conducting an X-ray diffraction study, the improved steps comprising:

(a) diffracting a source of X-ray energy to separate said energy into planes of energy of differing wave lengths;

(b) positioning an X-ray specimen :in a plane of a selected wave length and at an axis transverse to said plane;

(c) successively positioning a detector means in each of a plurality of positions in a detector cone about said axis and intersecting the specimen; and,

(d) detecting radiation diffracted by said specimen with said detector means while in each of said plurality of positions.

19. In a method of conducting an X-ray diffraction study, the improved steps comprising:

(a) diffracting a source of X-ray energy to separate said energy into planes of energy of differing wave lengths;

(b) positioning an X-ray specimen in a plane of a selected wave length and at an axis transverse to said plane; and,

(c) detecting radiation diffracted by said specimen with a detector means in each of a plurality of positions in a detector cone about said axis and intersecting the specimen.

References Cited UNITED STATES PATENTS 3,105,901 10/1963 Ladell et a1 250-515 3,213,278 10/1965 Spielberg 250-51.5 3,322,948 5/1967 Baak et a1. 250-515 RALPH G. NILSON, Primary Examiner.

A. L. BIRCH, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 594 ,255 July 23 1968 Thomas C. Furnas, Jr.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 21, "for" should read or Column 3,

line 25, "(l,)" should read (l, -1) Column 8, lines 71 and 72, cancel "(on the side of the goniostat opposite said detector)". Column 10, line 12, "aixs" should read axis Signed and sealed this 27th day of January 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Edward M. Fletcher, 11'.

Commissioner of Patents Attesting Officer

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