US3445653A - X-ray monochromator of linear type - Google Patents

Description

y T969 TERUICHI TOM'URA 3,445,653

X-RAY MONOCHROMATOR OF LINEAR TYPE Filed Oct. 4, 1965 Sheet I of s L= 2R Sine M zdsme=rfl 3 I Lg"? INVENTOR. TERUICHI Tom uRn BY J! ZLIWJ mum 0, 1969 TERUICHI TOMURA 3,445,653

XRAY MONOCHROMATOR OF LINEAR TYPE Sheet 2 01'3 Filed on. 4, 1965 FIG.3

INVENTOR. TERomHl ToMuRA BY -A alum I'll mailer May 20, 1969 TERUICHI TQMURA 5 X-RAY MONOCkROMATOR OF LINEAR TYPE Filed Oct. 4. 1965 sum 3 or a INVENTOR. HER we H 1 76M 0 R H I BY (Slu -J mas/em United States Patent Office 3,445,653 Patented May 28, 1969 3,445,653 X-RAY MONOCI-HIOMATOR F LINEAR TYPE Teruichi Tomura, Kodaira-shi, Tokyo-to, Japan, assignor to Kabushiki Kaisha Hitachi Seisakusho, Tokyo-to, Japan, a joint-stock company Filed Oct. 4, 1965, Ser. No. 492,616 Claims priority, application Japan, Oct. 10, 1964, 39/ 57,528 Int. Cl. G01n 23/20 US. Cl. 25051.5 4 Claims ABSTRACT OF THE DISCLOSURE A linear type X-ray monochromator constructed by a first link connecting four points consisting of a first pivot disposed at one point spaced apart by" a specific distance from the center of a Rowland circle, a first terminal point, on which an analyzing crystal is mounted, a second terminal point, and a second pivot disposed at the intersection point of the Rowland circle and an auxiliary circle having the same radius as that of the Rowland circle and a center thereof at the point spaced apart from the center point by a specific distance, both points being fitted movably along two straight lines intersecting at an X-ray source to form a certain angle and always to exist on the circumference of the Rowland circle; and a second link connecting three points consisting of a third pivot disposed at a point on a straightway guide movably fitted on the second pivot so as to be spaced apart from the point by a distance equal to the distance between the X-ray source and the first terminal point, and a third terminal point from the point on the straightway guide by a distance equal to the above specific distance; and one end of a lever having a length equal to the above specific distance is secured to the point, and the other end is movably fitted on the straightway guide, whereby a focusing point of the diffracted X-ray can be obtained on the circumference of the Rowland circle.

This invention relates to an X-ray monochromator, and more particularly to a new X-ray monochromator, in which an analyzing crystal and an X-ray detector are respectively constructed to move along straight lines with a constant mutual distance therebetween, the straight lines intersecting with each other in an X-ray source at a certain constant angle therebetween, so that the crystal, the X-ray source and the X-ray detector may be always maintained on a Rowland circle.

It is a general object of the present invention to overcome certain difficulties which accompany conventional X-ray monochromators.

More specifically, an object of the invention is to provide an X-ray monochromator of linear type which facilitates shifting of the Rowland circle to a suitable position along a circular locus.

Another object of the invention is to provide an X-ray monochromator wherein various parts such as the crystal, links, and pulleys can be assembled with separated pivots, whereby the thickness of the entire apparatus can be substantially reduced.

A further object of the invention is to provide an X-ray monochromator of a construction and arrangement, wherein no part exists in front of the bent crystal in case an asymmetrically cut crystal is used, whereby analysis of shorter wavelengths becomes possible'and the range of use can be expanded.

The nature, principle, and details of the persent invention will be more clearly apparent from the following detailed description when it is read in conjunction with the accompanying drawings, in which like parts are designated by like reference numerals and characters, and in which:

FIGS. 1 and 2 are schematic geometric views for description respectively of focusing and linear type X-ray spectroscopic methods;

FIG. 3 is a schematic geometric view for description of the principle of the present invention; and FIGS. 4, 5, and 6 are schematic geometric views show- 1ng preferred embodiments of the X-ray monochromator according to the invention.

As conducive to a full understanding and appreciation of the nature and utility of the present invention, the following brief consideration of the principles of the focusing and linear type X-ray spectroscopic methods is presented.

Referring to FIG. 1 indicating the principle of a focusing type X-ray monochromator, if a crystal having curved net planes as designated by reference numeral 4 (arcs of concentric circles with their centers at point 3) is used, X-ray beams passing through a point 1 will be diffracted and will always pass through a point 2. That is, divergent X-rays passing through the point 1 (or X-rays emitted from point 1 as an X-ray source) are assumed to be diffracted over the entire span of the curved net planes of. the crystal, whereby sensitivity of the X-ray mono chromator would theoretically be increased. However, since it is difiicult to produce such a crystal with net planes so curved, and the arrangement or construction of the X-ray detector becomes very complicated when using this crystal, such crystal cannot be used in practice for X-ray analysing purposes. Accordingly, bent or curved crystals of either a symmetrical type having the part 5 of the above-mentioned curved net planes, or a symmetrical type having the part 6 are generally used.

In this case, the position 1 of the X-ray emission point, the bent crystal 5 (or 6), and the focusing point 2 are always on the same circle 8, which is generally called the Rowland circle. The angles a and 13 at the circumference both of which are subtended by the are 1-3 are equal to each other, and their complementary angles are also equal. Therefore, the angle subtended by the are 1-7 becomes 20, which is equal to that subtended by the are 2-7.

That is, both central angles are equal, and each is equal to two times the X-ray grazing angle 0 (the angle of intersection between the aforementioned net plane which participates in the diffraction and the incident X-ray) as indicated in FIG. 1, therefore, the chord L (length of the segment 10) and the chord La (length of the segment 11) are equal, and, moreover, this chord L is proportional to the wavelength of the diffracted X-rays.

FIG. 2 indicates the principle of linear type X-ray spectroscopy which will now be considered. If a bent crystal 5 is shifted as indicated by designations 5a and 5b along a straight line 10, and its Rowland circle 8 is revolved so as to pass always through the X-ray emission point '1 as indicated by designations 8a and 8b, the focusing conditions will be constantly satisfied. In this case, the focusing point 2 in moving through corresponding positions 2a and 2b describes a complicated path resembling a part of a lernniscate as indicated by doted line 12.

Since the direction of the analyzed X-ray beam from source 1 is constant in this system, this system is suitable for use in electron probe microanalyzers and fluorescent X-ray analyzers, in which constancy of X-ray take-off angle is important, and, furthermore, has the advantage of afford-ing direct reading of the X-ray wavelength by the displacement distance.

In FIG. 1, as the Rowland circle 8 is shifted through positions 8a and 8b, the corresponding positions of its 3 center 9 are 9a and 9b, and those of a slit 13- and detector 14 are 13a, and 14a, 14b, respectively.

The conventional X-ray monochromator of linear type as above described is so constructed that the center 9 of the Rowland circle undergoes a circular motion around the X-ray emission source 1. However, the above-mentioned direct control of the circular movement of the Rowland circile center is very diflicult to be attained because of restrictions imposed by actual construction of the X-ray source. For example, in order to obtain such circular locus 9, 9a, 9b of the Rowland circle center as shown in FIG. 2 it is necessary to take the point 1 as the center of the circular locus, though the specimen to be analyzed must be placed at this point 1. Therefore, a pivot shaft or other elements for allowing the direct circular movement of the Rowland circle center must be disposed at this point 1, so as not to interfere with the positioning of the specimen at the point 1 as well as projeotion of the incident electron beam 15 with respect to the specimen therefor. But it is very difficult in practice to realize such mechanism. As alternative measures, an arcuate guide, etc., have been used so as to establish the circular locus of the Rowland circle center. However, such alternative mechanism is obstructive to the positioning of other elements, for example, employment of specimen fine moving mechanisms is restricted by the establishment of the arcuate guide, whereby the range of the X-ray wavelength to be analyzed is greatly restricted. The above-mentioned arcuate guide is obstructed by mechanisms such as that for causing fine movements of the specimen, and in many such cases, restriction of the wavelength range of X-rays which can be analyzed is imposed.

The present invention contemplates the elimination of the above described difficulties by providing an X-ray monochromator of linear type wherein the principal operation of the linear type X-ray monochromator as shown in FIG. 2 can be obtained by using more useful means than the conventional device, so that great many numbers of mechanical elements concentrated at the point 1 of the X-ray source may be reduced.

The principle of the present invention will first be described in conjunction with FIG. 3. In this FIG. 3, a Rowland circle 8 is shown to have a center 9 and a given radius. According to the present invention, an auxiliary circle 21 is employed in partially overlapping relation with the Rowland circle 8. This auxiliary circle 21 has a center 17 and the same radius as that of the Rowland circle and also produces intersecting points, one of which is designated by the numeral 19.

Now assume that the angles 7-9-19 and 9-1917 are designated as g and .5 respectively, a point such as point 22 that produces an angle 7-9-22 to be equal to 2 may be obtained on the Rowland circle 8. Once the point 22 has been obtained, a point is obtained by eX- tending a straight line 40 having a length as long as the distance between the point 1 and 22 from the point 19 to allow intersection of the straight line 40 with the auxiliary circle 21. From point 20, a point 18 is then obtained to produce a triangle A20-17-18 which is congruent with a triangle A19-9-17. Finally, the intersection of a straight line having a length as long as the distance between the points 18 and 20 with the line 40 having produced the required point 2. This relation will be explained as follows.

The Rowland circle center 9 is assumed to have been shifted to the point 17, the focusing point 2 is also assumed to have been shifted to a point 18 on the auxiliary circle 21 since the distance between the focusing point 2 and the point 8 is equal to the distance between the Rowland circle 9 and the auxiliary circle center 17. Therefore, the intersection between the points 19 and 17, and 9 and 2 respectively, is designated by numeral 48. The angles 19-48-2 and 19-17-18 are equal to each other. The

4 angle 7-9-2 is, therefore, shown in the following equation.

On the other hand, the angle 1-9-7 is represented by the following equation.

Since the triangles A1-9-22 and A19-17-20 are congruent, the angle 1-9-22 is equal to the angle 19-'17-20, so that This signifies that the point 2 is positioned symmetrically with the point 1 with respect to the point 7.

Now, the operability of the present invention is described when the inventive principle is in moving condition. First, an auxiliary circle 21 is to be determined to partially overlap with the Rowland circle 8. The center 17 thereof and the mutually intersecting point 19 are obtained. A first link is provided to connect the abovementioned points 17, 19, and 7 and a discretionary point 35 to each other with a mutually fixed relationship therebetween. This link is so facilitated that the points 7 and 35 are constrained to move along straight lines 38 and 49. It is a well established geometrical theorem that these points 7 and 35 always position themselves on the Rowland circle in a shifted state which is shifted around the point 1. Accordingly, once the point 7 is fixed at a certain position on the straight line 38, a point 22 will be obtained to satisfy the angular requirement as mentioned above, i.e., r2, and the distance between the points 1 and 22 is taken on a straightway guide 40 to fix the distance of a movable point 20 which is reciprocally movable along the guide from the point 19. This guide 40 is rotatably mounted around the point 19. A second link connecting between the point 17 and 20 with the same distance as the radius of the Rowland circle 8 and the auxiliary circle 21 is provided and the point 18 is associated therewith to form an isoceles triangle which is congruent with the triangle A9-19-1'7. Finaly, point 2 is movably mounted to the guide 40 which is constrained to move along the guide with a link 39 of fixed length, the length of which is the same as that of the base link of the isosceles triangle. According to the present invention, the point 22 may be in accord with either the point 7 or the point 19.

The required components of the X-ray monchrornator according to the present invention are as follows:

(a) A first link for connecting four points consisting of a first pivot disposed at a given point 17 spaced apart by a specific distance from the center 9 of a Rowland circle 8, a first terminal point 7 at which an analyzing crystal is mounted, a second terminal point 35, points 7 and 35 being on the circumference of the Rowland circle 8, and a second pivot disposed at the intersection point 14 of the Rowland circle and the auxiliary circle 21 having the same radius as the Rowland circle and a center at the point 17;

(b) Means for securing the point 7 and the point 35 to be respectively movable along two straight lines intersecting at an X-ray source to form a given angle on the circumference of the Rowland circle 8;

-(c) A straightway guide secured to the second pivot;

(d) A second link for connecting the three points consisting of a third pivot movably disposed at a point 20 on the straightway guide spaced apart from the point 19 by the distance equal to that between the X-ray source and the point 7, or the point 19, or a point 22 at the other end of the base triangle A7-9-22 having a vertex angle o'(o'=2) 9-1917)-( 7-9-19) and a third terminal 'and the other is movably disposed on the straightway guide;

(f) Means for maintaining an X-ray detector disposed outside of the Rowland circle and on the extension of a straight line connecting between the point 7 and the intersection point 2 (focusing point) of the straightway guide and the other end of the lever; and

(g) Means for linearly moving the third pivot and the other end of lever in cooperation with the first link.

One embodiment of the invention as applied to an X-ray microanalyzer is shown in FIG. 4 (where 5:25), in which the same reference numerals and characters as those of FIG. 3 are used. In addition, an electron beam 15, an electron lens 33, and a specimen 16 are shown.

In FIG. 4, analyzing crystal 5 is provided at the terminal point 7 of a first link 31 for connecting points 717-359 with each other, where the respective points 7 and 35 are movably disposed along two straight lines and 23 which intersect with each other at an X-ray source 1 to form a certain angle 5 therebetween. It is apparent from the above description that the distance between the points 7 and 35 is kept constant. Accordingly, it is possible to cause the points 7, 1 and 35 to exist on the Rowland circle 8 whose center is always on a circumference of a circular locus around the X-ray source 1 having the same radius as that of the Rowland circle. The second link 32 for connecting points 17-20-18 is rotatable around the point 17, and the point 20 of the link 32 is secured movably on a straightway guide 24 whose one end is rotatably secured to the point 19. Also, pulleys 26 and 27 are respectively disposed on the points 7 and 19 and lever 39 is secured between the point 18 and the movable point 2 (focusing point) on the straightway guide 24. Moreover, a tension member is provided to pass around pulleys 26, 27 and 28 as shown in FIG. 4 and is secured to the point 20 at one end thereof. An X-ray detector 30 is disposed outside of the Rowland circle 8 on the extension of a straight line connecting both points 2 and 7. In such construction, the end point 2 of the lever 39 will always coincide with the X-ray focusing point, whereby X-rays diffracted by the crystal 5 can be properly focused at the focusing point. Therefore, the diffracted X-rays pass through a slit 29 mounted at the point 2 and are detected by the detector 30.

In this case, since the rotational angle of the link 31 is set to be equal to that of the quide 2, by using the pulleys 26 and 27 having the same diameter, the lengths of the tension member 25 wrapped respectively about the pulleys are equal to each other and the respective wrapped directions are opposite. Therefore, regardless of the position of the Rowland circle 8, the distance between the point '19 and 20 is maintained by the tension member 25 so as to be equal to that between the points 1 and 7. Here, since the angle .5 shown in FIG. 3 is selected to be equal to 2g in the example shown in FIG. 4, the point 22 of FIG. 3 will coincide with the point 7.

Then, if a third link 32 connecting points 17-20-18 and a straightway guide 24 are engaged respectively with pivots provided at fixed points 17 and 27 fixed to the second link 31, and the distance between points 19 and 20 is maintained equal to the distance between points 1 and 5 by means of a tension member 25, the extremity point 2 of a link 39 mounted on the pivot 18 will always coincide with the X-ray focusing point as is apparent from the foregoing consideration.

Then, since the angular relationships are so selected that (angle 7-219)= /2 (angle 7-919)= /2 and that =2, X-rays can be focused at a detector 30, irrespective of the movement of the Rowland circle, by mounting a slit 29 at the point 2 and the detector 30 on a line angularly displaced by the fixed angle 5; from the axis of the straightway guide 24. Since the angle 5; shown in FIG. 3

is selected to equal 2g in the instant example shown in FIG. 4, the point 22 of FIG. 3 coincides with the point 7.

The above mentioned tension member 25 is passed as shown in FIG. 4 around pulleys 26 and 27, the diameters of which are so selected that the lengths of the tension member 25 wrapped respectively about the pulleys are equal and, being of opposite direction, are mutually cancelled since the rotational velocity of the link 31 around the pivot 17 is equal to the rotational velocity of the guide 24 around the pivot 19 relative to the link 31.

In order to prevent this tension from slackening, it is necessary to impart tension thereto by means such as a spring (not shown) at point 20. It is not necessary, of course, to construct the links 31 and 32 with only straight lines, other configurations being suitable for these links provided that they establish the correct positions of the pivots.

Another embodiment of the invention as shown in FIG. 5 illustrates the case wherein the angular relationship in FIG. 3 is expressable by =2, that is, and point 22 is caused to coincide with point 19. More specifically, in place of the tension member 25 of the example shown in FIG. 4, there is provided a tension member 25a such as to establish a distance between said center of the bent crystal and the focusing point which distance is equal to the distance between the X-ray point source and said intersection of said two circles. The construction of the other parts are the same as those shown in FIG. 4.

In this case, however, in order to provide compensation for the number of windings of the tension member around the pulleys, a pulley 27a and a pulley 41 of a diameter twice that of the pulley 27a are used as shown since, with a rotational ratio of the link 31, guide 24, and link 32 of 1:2:3, the rotational difierence between the guide 24 and the link 32 is 321=1, and the extreme end of the tension members 25a is fixed to the link 32. Furthermore, by using pulleys of the same diameter as 27a at points 20, 18, and 2, any difference in the lengths of the tension member can be cancelled out.

A further embodiment of the invention as shown in FIG. 6 is suitable for the case wherein an asymmetrically cut crystal is used which is placed at the point of intersection of said two circles and wherein a link for driving this crystal is provided. In this case, since there is no special mechanical part in front of the bent crystal 6, and the segment 10 is proportional to the Wavelength of the X-rays to be diffracted, direct reading of the X-ray wavelength is possible at point 47 to which point 7 has been parallelly moved. For this reason, the bent crystal 6 is indirectly driven by means of links 44 and 45. The fact that at this time the movement of the pivot 47 is proportional to the wavelength will be quite apparent from the fact that the imaginary point 7 is being parallelly moved. That is, except for the mechanism for moving the bent crystal 6, the construction of the instant example is the same as that shown in FIG. 5.

According to the present invention as described above, it is possible to avoid obstruction by parts such as an electron lens by causing the centre of the Rowland circle to shift to a suitable position, whereby the distance between the specimen to be measured and the analyzing crystal, that is, the range of usable X-ray wavelengths, is widened. Furthermore, since the various parts such as the crystal, links, and pulleys can be assembled in dispersed state, the thickness of the entire apparatus can be reduced relative to that of a conventional apparatus wherein these parts are concentrated at one point, whereby the present invention is highly suitable for cases where a large number of spectroscopes are used in combination.

The present invention afiords further advantages such as the possibility of construction wherein no parts exist in front of the bent crystal in the case where an asymmetrically cut crystal is used, whereby dispersion of short wavelengths becomes possible, and the range of use is expanded. Accordingly, the present invention is highly effective in applications to instruments such as X-ray probe microanalyzers and fluorescent X-ray analyzers.

It should be understood, of course, that the foregoing disclosure relates to only preferred embodiments of the invention and that it is intended to cover all changes and modifications of the examples of the invention herein chosen for the purposes of the disclosure, which do not constitute departures from the spirit and scope of the invention as set forth in the appended claims.

What I claim is:

1. A linear type X-ray monochromator comprising: an X-ray source; an analyzing crystal; an X-ray detector; a first link for connecting four points consisting of a first pivot disposed at a certain point (17) spaced apart by a distance smaller than the diameter of the Rowland circle from the center (9) of a Rowland circle (8); a first terminal point (7 on which the crystal is mounted; a second terminal point (35), said first and second terminal points (7 and 35) and the X-ray source being positioned on the circumference of the Rowland circle, and a second pivot disposed at an intersection point (19) of the Rowland circle and an auxiliary circle (21) having the same radius as that of the Rowland circle and a center thereof at the certain point (17); means for reciprocably constraining the first and second terminal point (7 and 35) to move along two straight lines, respectively, which intersect each other at an angle smaller than 180 at the X-ray source; a straightway guide pivotally secured at one end thereof to the second pivot; a second link pivotally mounted to the first link at the first pivot for connecting the three points consisting of the first pivot, a third movable pivot disposed at a second point (20) which is constrained to move on the straightway guide so as to be spaced apart from the intersection point (19) by a distance equal to the distance from the X-ray source to such a third point (22) which provides an isosceles triangle A7-9-22 having a vertex angle 0', where 0' is designated by a=2( 91917)( 7919), and a third terminal point (18) so that an isosceles triangle AIS-1740 congruent to the triangle A7-9-22 may be obtained; a lever (39) having a length equal to the distance between the center and said certain point (9 and 17), one of its ends being pivotally fitted to the third terminal point (18) and the other constrained to move along the straightway guide; means for maintaining the X-ray detector outside of the Rowland circle in a straight line connecting the first terminal point (7) and the intersection point positioned at the intersection of the straightway guide and the other end of the lever, the X-ray focusing slit being disposed at a focusing point (2); and means for linearly moving the third pivot and the other end of the lever in cooperation with the first link.

2. The X-ray monochromator according to claim 1, wherein the third movable pivot is spaced apart from the intersection point (19) by a distance equal to the distance from the X-ray source to the first terminal point (7 3. The X-ray monochromator according to claim 1, wherein the third movable pivot is spaced apart from the intersection point (19) by a distance equal to the distance from the X-ray source to the intersection point (19).

4. The X-ray monochromator according to claim 1, which further comprises a tension member, one end of which is fixed and the other secured to the second point (20), and at least two pulleys about which the tension member is wrapped in opposite directions.

References Cited UNITED STATES PATENTS 2,898,469 8/1959 Rose 250-5l.5 3,073,952 1/1963 Rose 25051.5 3,123,710 3/1964 Neuhaus 250--51.5

RALPH G. NILSON, Primary Examiner.

S. C. SHEAR, Assistant Examiner.

US. Cl. X.R.

Images