US 3852594 A
An X-ray diffraction apparatus comprising means for rotating a specimen in the path of an X-ray beam and means for rotating a diffraction slit simultaneously with the specimen but at a lower angular velocity, so that the X-ray irradiated portion of the specimen remains substantially constant in size during such rotation.
Claims available in
Description (OCR text may contain errors)
United States Patent 1191 Paolini 1111 3,852,594 1451 Dec. 3, 19m
[ X-RAY DIFFRACTION APPARATUS  Inventor: Frank Rudolph Paolini, Stamford,
 Assignee: Pepi Inc., New York, NY.
 Filed: July 25, 1973 21 Appl. No.1 382,481
 US. Cl 250/278, 250/273, 250/272  Int. Cl. GOln 23/00  Field of Search 250/277, 278, 491, 279,
 References Cited UNITED STATES PATENTS 1/1959 Neff 250/278 7/1961 DeLong et a1. 250/505 3/1964 Zingaro 250/278 3,361,909 1/1968 Talas 250/278 3,411,000 11/1968 Schliephake et al 250/278 3,566,111 2/1971 Harm 250/278 Primary ExaminerArchie R. Borchelt Assistant Examiner-B. C. Anderson Attorney, Agent, or Firm-Frank R. Trifari  ABSTRACT An X-ray diffraction apparatus comprising means for rotating a specimen in the path of an X-ray beam and means for rotating a diffraction slit simultaneously with the specimen but at a lower angular velocity, so
- that the X-ray irradiated portion of the specimen re mains substantially constant in size during such rotatlOl'l. 7
7 Claims, 5 Drawing Figures LENGTH IRRADIATED 8 (mm) PATENTEL C sure-r ear 2 lo Q 0 IO 20 so 40 5 6O 7O 8O ANGLE OF INCIDENCE 9 (deg) X-RAY DIFFRACTION APPARATUS BACKGROUND OF THE INVENTION X-ray diffraction, the divergence slit serving to form an X-ray beam having desired geometric characteristics. During X-ray diffraction analysis the specimen being investigated is rotated about an axis lying in its upper flat surface, to cause the X-raybeam to impinge upon the specimen at various angles, the rotation being so that the angle (0) between the specimen surface and a line drawn from the X-ray source to the center of the irradiated portion thereof ranges between 0 and 90.
During such X-ray diffraction analysis the divergence slit remains stationary, so that, because of the rotation of the specimen with respect to the divergence slit and as a result of geometric considerations, the area of the specimen irradiated by the X-ray beam varies between a relatively small amount when the value of 6 is high (e .g 80) and arelatively large amount when the value of 6 is low (e.g., l0). Such variation of the irradiate area is highly undesirable because of numerous adverse effects on the accuracy and reliability of the analysis.
To cope with such variation of the irradiated area, the prior art has resorted to using, during each diffraction analysis, stationary divergence slits of various fixed sizes, with larger slit openings being employed for large 0 values and smaller slit openings being employed for smaller 6 values, thereby tending toequalize the irradiated area of the specimen as it is rotated over the range of 6 values. Such a practice is undesirable because interchanging the divergence slits is 'a time-consuming process and because it is necessaryto have available a number of such divergence slits of various sizes, which can be an expensive proposition, and even more impor tant, because interchaning thedivergence slits still results in a significant amount of variationin the X-ray irradiated of the specimen.
While the prior art has proposed various method for controlling the irradiated specimen area (see, for example, M. Loisel, Bulletin de la Societe Francaise de Ceramique," Issue No. 90, Jan. March 1971, pp. 55 et seq.) such have not been fully desirable nor useful, by reason of, inter alia, their operating on a gross scale that is insufficiently precise for the very important small angular values (9) of specimen orientation.
The present invention overcomes, the above shortcomings by providing an apparatus permitting the rotation of the divergence slit in conjuction with the rotation of the X-ray irradiated specimen, whereby the dimensions of the X-ray irradiated portion of the specimen remain substantially constant during the rotation of the specimen. In a preferred embodiment, the divergence slit is connected to a structural'element linked with a second structural element connected to the specimen such that the divergence slit rotates at a lower angular speed than the specimen such that the X-radiation is cut off from the specimen when the 0 value reaches zero.
DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic representation of a prior art X-ray diffraction apparatus. 7
FIG. 2 is an isometric view of the X-ray diffraction apparatus of thepresent invention.
FIG. 3 is a schematic representation depicting a feature of the present invention.
FIG. 4 is a fragmentary sectional elevation view of a diffraction slit of the type employed in the present invention.
FIG. 5 is a number of curves depicting results obtained with the present invention.
THE PREFERRED EMBODIMENT FIG. 1 depicts the situation in the prior art where the X-ray diffraction specimen 10 is rotated with respect to a stationary divergencejslit 11 through which there passes X-radiation 12 from a source 13. When the specimen 10 is acutely disposed (i.e., 0,, is less than to an imaginary line 14 extending between the X-ray source and the center of the irradiated portion of the specimen, the portion of the specimen impinged by the X-radiation has a dimension S whereas the impinged portion dimension S .when when 0,, equals 90 (shown in broken lines) is substantially less than S Such deviations in the dimensions of the X-radiation impinged portion of the specimen are unsatisfactory, as mentioned above.
FIG. 2 depicts a portion of the X-ray diffraction apparatus 20 in accordance with the present invention, containing and X-ray line source 22, as so-called Soller slit assembly 24, a rotatable divergence slit 25 mounted via a shaft to a cog wheel 26, a specimen holder 27 connected to a second cog wheel 28, the X-ray diffraction analysis specimen 29 which is mounted on the holder 27, the second cog wheel 28 being driven by'a drive shaft 30 whose rotatio'ii speed is co-ordinated with the rotation speed of the goiiiometer'(not shown) used with the diffraction apparatus, a mechanical linking means 31 (i.e., cog belt) linking the 'cog wheels 26 and 28, and a receiving slit 32, a Soller slit 33 and an anti-scatter slit 34 all (i.e., 32, 33, and 34) located between the specimen and the detector 35. It is essential that the divergence slit'cog wheel 26 include a number of teeth greater than that of the specimen cog wheel 28 (i.e., a slit cog to specimen cog tooth ratio greater than 1) so that the former rotates at a lower angular speed (i.e., provides a smaller corresponding angular displacement) than the former, it being especially preferred that the tooth ratios of these cog wheels be adjusted such that the beam be cut off from the specimen upon the 6 value reaching zero degrees and that the slit plane and the irradiated specimen surface be substantially parallel when 6 is 90.
By way of the explanation, reference is made to FIG.
. 3 where there are depicted the divergence slit cog where is the angular displacement of the specimen cog wheel 28 and 6,, is the initial angular displacement of the slit cog wheel 26 with respect to specimen cog wheel 28 (i.e., the initial angular disposition of the slit with respect to the specimen irradiated surface). By virtue of the diffraction slits having a finite thickness, the beam is cut off from the specimen before 6 reaches zero, so that the geometry ofthe diffraction slit should be considered in order that X-ray beam extinction occur (i.e., the beam is cut off from the specimen), under optimal conditions, when 6 equals exactly 0. Therefore, assuming a diffraction slit having substantially the geometry shown in FIG. 4, wherein r represents the radius ofjthe cylindrical slit-defining portion 40 defining the slit opening 42, w represents the width of the opening 42 and t represents the thickness of the slit-defining body 43. While the slit is shown with cylinefining portions, other geometries can be rectangular slit-definingportions. An imaginary line from and tangent to one face 44 of the slitdefining portion 40, to and tangent to the opposite such face 46 forms an angle, c, with the slitdefining body 43. Therefore, the following expressions can be derived. Where q the extinction, or beam cut off, angle, e, can be deter- 1 mined by the following expressions:
sin e r/k so that e sin (r/k) q- Optimally, X-ray beam extinction occurs exactly when 6 0,50 that it is preferred that 0 e at 0= 0. Substitiuting these conditions into Equation 2 under this optim'al condition results in the expression:
i if 0,, isgreater-than e, the length (S) of the X-ray irradiated portion of the specimen increases rapidly as 6 approaches zero. whereas a value of 6 less than 6 results in a decrease of the irradiated portion lengths as 6 approaches zero. The latter situation (i.e., 9 e) results in premature extinction. in that the irradiated portion length is zero at some 0 value greater than zero. Y it is further optimal that 0' 90 when 0 90, so that there is achieved an irradiated specimen portion of. maximum length for values of 6 approaching 90.
Re-writing Equation 4 to satisfy this second optimal condition 0, 90 N/N (90) e Equation 6 establishes the condition that must be met by numbers N and N of cog wheel teeth. N and N must also, of course, be integers. In practice, one picks values that most'closely satisfy Equation 6.
EXAMPLE 1 Using a diffraction slit having a cylindrical slitdefining body with a radius r of 0.60 mm, a body thickness t of 1.20 mm, and a slit opening width w of 5.00 mm, the value k of the diffraction slit is 3.10 mm and the extinctionan gle, e, is determined from Equation 3 to be 11 l0.-Therefore, when 6 0, 0,, should optimally be 11 l0 and, as a second optimal condition, when 6 90, 6 should also be 90. From Equation 6, the cog tooth number ratio, N/N' for the specimen and slit cog wheels should be about 79:90 for maintaining an irradiated specimen portion of substantially constant dimensions, this being done automatically during the specimen rotation. i I
Using the values 6,, ll0 feet and an NrN' tooth number ratio of 79:90 and assuming a distance of 172.00 mm, between the center of the irradiated specimen portion and the X-ray source and a distance of 72.00 mm between the X-ray source and the slit center, the length, S, of the irradiated portion of the specimen was calculated for 0 valves over the range of 0 to the resulting S values being shown as Curve l in FIG. 5. In this situation 0 equals 90 when 6 is 90.
.With these same values, except for 0,, 1 1 10 feet,
the length S of the irradiated portion of the specimen was calculated for 0 values over the range of 0 to 90, the resulting S values being shown by Curve ll in FIG. 5. The significant improvement provided by setting 0,, at exactly the value of e is seen from the comparison of these curves, the length, S, of the irradiated portion in Curve ll not exhibiting the relatively sharp drop for the S value for very low 6 values i.e., about 6 5. With these same values, except for 6,, and a tooth ratio N:N of 90:90 for the slit and specimen cog wheels, the S value was calculated over the range of 6 0 to- 0 90, the results being depicted as Curve ill in FIG. 5. The significant improvement provided by the present invention is seen-from the comparison of these Curves, the length, S, of the irradiated portion remaining substantially'constant over substantially all'of the range between 6 Oto 0 90 (Curves land ll) when the slit cog: specimen cog tooth ratio is greater than 1 (i.e., 90:79), whereas, as shown by Curve Ill, the length, S drops dramatically for 0 values below about 0 50 and is zero at about 8 12 for the situation where the cog wheels have the same number of teeth (i.e. N N).
Thus, the present invention permits achieving an irradiated specimen portion of substantially constant dimensions over the rotation range for analyzed specimen. While setting 0,, at exactly eleads to a deviation of 0 from 90 when 6 equals 90, it is felt to be more preferable to set 6., at exactly the value of the extinction angle,,e, notwithstanding the fact that 6' will not equal 6 at 6 90, in order to avoid the drop in S values about 0 equals 5 and less.
1. An X-ray diffraction apparatus comprising:
a. a source of X-rays;
b. means for holding an X-ray diffraction specimen in the path of said X-ray beam such that a portion of said specimen can be impinged by said beam;
c. means for rotating said specimen at a first angular velocity from a first position to a second position;
cl. a diffraction slit disposed between said specimen and said source such that said X-rays pass throug the opening of said slit;
e. means for rotating said diffraction slit simultaneously with the specimen, said difiraction slit being so rotated at a second angular velocity lower than said first angular velocity; and
f. means for measuring the intensity of X-rays reflected from said specimen, whereby said irradiated portion remains substantially constant throughout the rotation of said specimen.
2. An'X-ray diffraction apparatus as defined in claim 1, wherein at said first position said position is substantially perpendicular to an imaginary line extending from said X-ray source to the center of said portion and said second position said portion is substantially parallel to said imaginary lines and said diffraction slit is rotated between third and fourth positions, said diffraction on slit at said third position being substantially parallel to said specimen at said third position being substantially parallel to said specimen at said first position and at said fourth position being obliquely disposed to said specimen at said second position.
3. An X-ray diffraction appparatus as defined in claim 1, wherein said means for rotating said specimen comprises a first cog wheel and said means for rotating said diffraction slit comprises a second cog wheel driven by said first cog wheel. 7
4. An X-ray diffraction apparatus as defined in claim 3, wherein the gear ratio of said first cog wheel to said second gear wheel is less than one.
5. An X-ray diffraction apparatus as defined in claim 4, wherein said first gear wheel is mechanically linked to and drives said second gear wheel.
6. An X-ray diffraction apparatus as defined in claim 3, wherein the angular displacement 6' of said second gear wheel is determinable from the expression:
where N and N are the teeth numbers for said first and second gear wheels, respectively;
0 is the angular displacement of said first gear wheel;
and 1 e is the angular orientation of said second gear wheel when said beam iscut off from said specimen located at said second position.
7. A method of operating an X-ray diffraction apparatus comprising the steps of: r
a. providing an X-ray beam source;
b. providing an X-ray diffraction specimen disposed at an angle of substantially zero degrees with respect to said X-ray beam;
c. providing an X-ray diffraction slit between the source of said beam and said specimen, said diffraction slit being disposed at substantially the extinction angle thereof when said specimen is disposed at 0 with respect to said beam, said specimen being rotatable over a range of said angles of from zero to about 90 and said slit being rotatable I at a lower angular velocity than said specimen and over an angular range extending from said extinction angle to about 90;
d. irradiating said specimen with said X-ray beam and simultaneously rotating said specimen and said slit over said ranges of angles; and
e. measuring the intensity of X-rays reflected from said specimen.