A two piece ceramic soller slit collimator for x-ray collimation

Abstract: A Soller slit collimator and method of producing it for use in X-ray analysis, said collimator comprising two rectangular ceramic blocks (1, 2), each of said blocks being of essentially identical composition and configuration, each of said blocks containing heavy elements and being capable of absorbing X-radiation, each of said blocks having a plurality of parallel blades (11) projecting out of a solid wall portion (12, 13) of said block and in contact and parallel facing relationship with a corresponding blade of said other block and said blocks being adhesively bound to said other at corres­ ponding surfaces (18-21) of upper and lower wall portions of said blocks.

Description: The invention relates to a method of producing a collimator for use in X-ray analysis, and to a collimator for use in X-ray analysis produced with that method. In X-ray analytic instruments employed for characterization of materials such as X-ray diffraction apparatus or X-ray spectrometers it may be desirable that the incident and/or exciting beams be collimated to parallel beams in order to minimize axial divergence. In powder diffractometers reducing axial divergence of the beams improves the resolution and precision of the angular measurements and eliminates smearing aberrations. In X-ray spectrometers fine collimation of the incident beams is necessary to improve sensitivity of measurements. In other X-ray instruments such as X-ray diagnostic apparatus such as is used in computer assisted tomography fine collimation can act to eliminate image blurring. In USP 3,988,589 a radiation collimating arrangement is described which comprises blocks of a composition capable of absorbing radiation and being formed out of one single piece of material, each of the blocks having a plurality of parallel blades projecting out of a solid portion of that block, the blades thus being separated by grooves and the blocks being adhesively bound to each other. In this document the blocks obtain their shape by casting. The parallel blades projecting at one side out of the solid portion of one block engage with shallow recesses at the other side of another block. In this way a mortis-tenon connection is obtained to prevent radiation leaking through the collimator in the not collimated direction. For X-radiation there exists a preference for collimation by use of Soller slit collimators. The use of these co]limators is well documented and is described for example in M.P. Klug and L.E. Alexander, X-ray Diffraction Procedures, New York, John Wi]ey & Sons, 1954, pages 241, 242, 251-253 and 275-277; Brandt et al U.S. Patent 4,361,902, Wolfel U.S. Patent 4,364,122;25 Jenkins V.S. Patent 4,322,618 and Kusumoto et al U.S. Patent 4,284,887. A Soller slit collimator that is frequently used comprises a stack of thin blades parallel positioned, separated by narrower spaces and clamped together into housing assembly. The blades are formed of foils of materials absorbent of the X-rays being employed. This type of collimator is quite expensive as it requires a large amount of hand assembly. Further the thinness of the blades and the narrowness of the spaces between the blades, and thus the fineness of the collimation is limited in these collimators by the fact that foil blades tend to warp when clamped into the assembly housing particularly as they become thinner. Thus, in order to improve the fineness of the collimation, it is necessary that such collimators be made longer. However, it is frequently desirable that the collimator be as short as possible. The method of producing collimators known from the already described USP 3,988,589 does nor require a large amount of hand assembly. However, this document does not itself address to the problem of warping of the blades of the Soller slit type collimator. It is an object of this invention to provide a Soller slit X-ray collimator of improved construction in which in which blade warping is avoided and which is able to achieve an improved degree of collimation. These objects are achieved by the method according to the invention which comprises the steps of: positioning two ceramic blocks of a composition capable of absorbing X-radiation and each having a flat surface (called sawing surface) in such a way that the respective sawing surfaces of the blocks are situated in a single flat plane, forming a plurality of narrow grooves perpendicular to the sawing surfaces, each of said grooves being separated from neighbouring grooves by a thin blade each of said blocks being provided with wall portions parallel to said grooves and being broader than the said thin blades, positioning said resultant grooved blocks in a facing relationship so that the sawing surfaces of the wall portions and of the corresponding thin blades of said blocks are in mutual contact and in an essential parallel relationship with each other, adhesively binding together said blocks along the corresponding sawing surfaces of the wall portions. In a preferred embodiment of the method according to the invention the plurality of narrow grooves is formed by precision dicing sawing as known per se from semiconductor processing. The operation of precision dicing saws is described, among other places, in Zimring U.S. Patent 4,557,599, the contents of which are hereby incorporated by reference. In general the width of the grooves is about 50 to 1000 microns and preferably from 180 to 300 microns. The thickness of the blades is frcm about 50 to 200 microns, preferably from about 100 to 200 microns even collimators with blades of only 25 microns thick being produced. Ceramic blocks that are particularly useful for the collimators of the invention are those containing such X-ray absorbing materials as those ceramics comprising oxides or salts of heavy metals, such as oxides of Pb, Zr and Yi or mixtures thereof being preferred. The ceramic block may be adhesively joined together by any suitable adhesive. Preferably adhesives are those that are curable by exposure to light or by a catalyst preferably at room temperature. Examples of adhesives that may be used are epoxy based adhesives and cyanoacrylate ester adhesives. A preferred embodiment of the invention will now be described with reference to the figures of the drawings, wherein: Fig. 1 is a diagrammatic view of an arrangement for providing grooves in the ceramic blocks employed in the method of the invention, Fig. 2 is a perspective view of a matched pair of ceramic blocks provided with grooves according to the method of Fig. 1. Fig. 3 is a perspective view of a Soller slit collimator of the invention formed from the grooved ceramic blocks of Fig. 2, and Fig. 4 is a diagrammatic view of a test set-up for determining the acceptance angle of a Soller slit collimator of the invention. EXAMPLE Rectangular ceramic blocks 1 and 2 each capable of absorbing X-ray radiation and of essentially identical compositions (comprising lead titanate in an amount such that the lead content is over 60% by weight) each being for example 12.5 mm long, 40 mm wide, and 6,5 mm thick were placed on a saw table 3 of a precision dicing saw in a manner such that the surfaces 4 and 5 of each of said ceramic blocks are positioned along a single axis and against the fence 6 of the saw table 3. The saw table 3 with the ceramic blocks is then translated in a direction parallel to said axis toward revolving saw blade 7 the axis of which is perpendicular to the direction of travel of said saw table. The saw table 3 is positioned and moved in relation to the revolving saw blade 7 so as to cause the saw blade 7 to cut grooves 8 and 9 in the surfaces called sawing surfaces of the ceramic blocks 1 and 2, respectively, said grooves 8 and 9 being positioned along a single axis and parallel to said surfaces 4 and 5 and each of said groves 8 and 9 having a width of about 0.250 mm, a length of about 12.5 mm and a depth of about 3 mm. The saw table is then translated in a direction parallel to the axis of the saw blade and towards surfaces of said ceramic blocks parallel to said surfaces 4 and 5 by means not shown in a distance of about 0.325 mm from said grooves 8 and 9 and then repeated the above-described sawing operations and translating movements of the saw table 3 so as to form a series of additional grooves 8 and 9 parallel to and identical with said first formed grooves 8 and 9 in the ceramic blocks 1 and 2, the resultant groove being separated one from the other by 0.83 thick and 12.5 mm long blades 10 and 11 projecting out of bottom wall portions 12 and 13 of ceramic blocks 1 and 2 respectively as shown in Fig 2. An adhesive coating, not shown, of a polycyano acrylate adhesive such as "Permabond 910" is then applied to surfaces 18, 19, 20 and 21 of the side wall portions 14, 15, 16 and 17, each pair of said surfaces 18 and 20, and 19 and 21 being separated one from the other by the blades 10 and 11 and grooves 8 and 9. Ceramic block 1 is then positioned in contact with ceramic block 2 in a manner such that adhesive coated surface 19 is in contact with adhesive coated surface 18 and adhesive coated surface 21 is in contact with adhesive coated surface 20 and blades 10 of ceramic block 1 are in contact with corresponding blades 11 of ceramic block 2 in a manner such that the axes of the blades 10 in ceramic block 1 lie parallel to with the axes of the corresponding contacting blades 11 of ceramic block 2. The adhesive layer is then allowed to harden, causing the two blocks 1 and 2 to adhere to each other and thereby forming soller slit collimator 22 provided with soller slits 23 as shown in Fig. 3. The acceptance angle of this collimator was then determined according to the following procedure which is described below and the test assembly for which is shown diagrammatically in Fig. 4. According to this procedure, and referring to Fig. 4, an X-ray beam 40 passing through an aperture 42 in a lead shield 44 of the same size as an open area of a soller slit 22 to be tested is caused to impinge on the soller slit mounted in the X-ray path on a rotatable table rotatable around an axis 50 perpendicular to an axis of the X-ray path. An X-radiation detector 46 and a ratemeter 48 are provided on the side of the soller slit collimator remote from the X-ray source. The rotary table with the soller slit collimator thereon is rotated until there is no count rate on the ratemeter. The rotary table is then rotated in the opposite direction and the count rate reading is taken, for example, every 10 minutes of the arc. The data obtained by employing the soller slit collimator of the example is tabulated in the following Table 1. It will be noted that the table of the acceptance angle for this soller slit collimator was measured with determined to be 2°10′ or 2.16° a satisfactory agreement with the theoretical or calculated acceptance angle β where β equals 2ϑ and tan ϑ equals the widths of the opening between the blades divided by the lenght L of the blades, in this example being 247 divided by 12.5 ϑ equalizing 1.1°β therefore equaling 2.2°.

Claims: A method of producing a collimator for use in X-ray analysis, the method comprising the steps of: positioning two ceramic blocks (1, 2) of a composition capable of absorbing X-radiation and each having a flat surface (called sawing surface) in such a way that the respective sawing surfaces of the blocks (1, 2) are situated in a single flat plane, forming a plurality of narrow grooves (8, 9) perpendicular to the sawing surfaces, each of said grooves (8, 9) being separated from neighbouring grooves by a thin blade (10, 11), each of said blocks (1, 2) being provided with wall portions (14, 15, 16, 17) parallel to said grooves (8, 9) and being broader than the said thin blades (10, 11), positioning said resultant grooved blocks in a facing relationship so that the sawing surfaces (18, 19, 20, 21) of the wall portions (14, 15, 16, 17) and of the corresponding thin blades (10, 11) of said blocks are in mutual contact and in an essential parallel relationship with each other, adhesively binding together said blocks along the corresponding sawing surfaces (18, 19; 20, 21) of the wall portions (14, 16; 15. 17). The method of Claim 1 wherein the plurality of narrow grooves (8, 9) is formed by sawing. The method of Claim 2 wherein the plurality of narrow grooves (8, 9) is formed by precision dicing sawing as known per se from semiconductor processing. A collimator for use in X-ray analysis produced with the method according to any one of the Claims 1 through 3, in which: the collimator comprises blocks (1, 2) of a composition capable of absorbing radiation and being formed out of one single piece of material, each of the blocks having a plurality of parallel blades (10, 11) projecting out of a solid portion (12, 13) of that block, the blades thus being separated by grooves, the blocks (1, 2) are adhesively bound to each other, characterized in that: the blocks consist of ceramic material, the blocks are provided with wall portions (14, 15, 16, 17) parallel to said grooves (8, 9) and being broader than the thin blades (10, 11), the adhesively binding of two of the blocks (1, 2) to each other is located at corresponding surfaces (18, 19; 20, 21) of the wall portions (14, 16; 15, 17), each of the blades of one block is in contact and in a parallel facing relationship with a corresponding blade of the other block. The collimator according to Claim 4 wherein the width of the grooves (8, 9) is between 50 to 1000 micrometers. The collimator according to Claim 5 wherein the width of the grooves (8, 9) is between 180 to 300 micrometers. The collimator according to Claim 4 wherein the width of the blades (10, 11) is between 25 and 200 micrometers. The collimator according to Claim 7 wherein the width of the blades (10, 11) is between 100 and 200 micrometers. The collimator according to any one of Claims 4 through 8 wherein the ratio (r) between the depth (d) of the grooves (8, 9) and the width (w) of the blades (10, 11) in which r=d:w is between 15 and 120.

Inventors: ZOLA JOHN JOSEPH, ZOLA, JOHN JOSEPH
Applicants: PHILIPS NV, N.V. PHILIPS' GLOEILAMPENFABRIEKEN
Application year: 1989
Main classification: G21K1
IPC codes: G21K1