Patent Application
20100086104
This application claims Paris Convention priority of DE 10 2008 050 851.9 filed Oct. 8, 2008 and EP 09 000 179.3 filed Jan. 9, 2009 the complete disclosures of which are hereby incorporated by reference.
The invention concerns an X-ray analysis instrument, in particular, an X-ray diffractometer, comprising
An X-ray analysis instrument of this type is disclosed e.g. in DE 10 2004 052 350 A1.
X-ray diffractometry is an efficient method for non-destructive chemical analysis of, in particular, crystalline samples. In modern X-ray diffractometers, the X-ray beam that is generated by an X-ray source is directed onto a sample via a multi-layer optics and the diffracted X-ray radiation is analyzed by a detector.
The multi-layer X-ray optics performs monochromatization and mainly shaping of the X-ray beam in an X-ray analysis apparatus with good efficiency. However, the structure of the multi-layer X-ray optics also determines the beam properties on the output side of the multi-layer optics. Physical values such as the input and output convergence, the focal lengths between the source focus and the image focus, the enlargement ratio and thereby also the size of the X-ray beam in the image focus must be determined prior to production of the multi-layer optics. In particular, it is not possible to vary the surface curvature of a multi-layer X-ray mirror or the layer separations in its multi-layers at a later time. For this reason, the multi-layer X-ray optics are basically inflexible.
One particularly important property in X-ray diffractometry is the convergence angle β, since the resolution of a diffractometer decreases with increasing convergence angle. Convergence collimators have been disclosed for adjustment to varying measurement requirements.
U.S. Pat. No. 7,386,097 describes several holes of identical diameter on a rotatably disposed disc of an X-ray analysis device, which generates a collimator function. A collimator can be continuously moved in a first direction through slight rotation of the disc, and a collimator can be moved in discrete steps in a second direction by changing to a different hole on a different radius of the disc. There are different hole sets with different hole diameters. A similar functionality can be obtained with a band having several holes.
U.S. Pat. No. 7,245,699 B2 discloses a Montel optics with a variable collimator that is mounted thereto, comprising two L-shaped collimator sections one of which can be moved along the angle bisector between the two mirror surfaces.
In both cases, the beam conditioning possibilities are limited. The perforated disc of U.S. Pat. No. 7,386,097 only allows stepped adjustment of the beam divergence (in correspondence with the hole diameter of the different hole sets) and also only stepped collimator shift in one direction. Moreover, the mechanical structure is very complex. The collimator mechanism of U.S. Pat. No. 7,245,699 B2 basically always collimates out a part of the X-ray radiation that is remote from the source.
It is the underlying purpose of the present invention to present an X-ray analysis instrument that offers a greater variety of beam conditioning possibilities in order to thereby improve the field of use of multi-layer X-ray optics.
This object is achieved by an X-ray analysis instrument of the above-mentioned type which is characterized in that the collimator mechanism comprises means for gradual movement of the aperture window in at least one direction transversely to the X-ray beam, the aperture opening is at least as large as the cross-section of the X-ray beam at the location of the aperture window, and the path of movement of the aperture window, which is accessible by the collimator mechanism, in the at least one direction is at least twice as large as the extension of the X-ray beam in the same direction at the location of the aperture window.
The inventive collimator mechanism enables selection of any portion of the X-ray cross-section with respect to the area ratio at the location of the aperture window by means of the aperture opening, and pass it to a downstream X-ray experiment. In order to adjust the portion of the X-ray beam cross-section, the aperture opening is made to overlap the X-ray beam cross-section in corresponding proportions. If the entire beam cross-section is desired, the aperture opening is adjusted to completely overlap the X-ray beam cross-section. Since the aperture opening is at least as large as the X-ray beam cross-section, the X-ray beam is thereby not collimated at all.
Due to the fact that the aperture window can be moved within a wide range, a partial area of the X-ray beam cross-section can be selected from two opposite sides. The X-ray beam generally has different properties in different regions of its cross-section such that the inventive collimator mechanism also facilitates selection of the properties of the transmitted X-ray beam portion. If the aperture opening is larger than the X-ray beam, VW>=AOE+RS preferably applies in the at least one direction, with VW: path of movement of the aperture window; AOE: extension of the aperture opening; RS: extension of the X-ray beam.
The at least one direction, in which the aperture window can be gradually moved over at least twice the extension of the beam, preferably extends from the portion of the X-ray beam cross-section that is close to the source to the one that is remote from the source. Particularly relevant properties of the transmitted X-ray beam can thereby be influenced.
In one particularly preferred embodiment of the inventive X-ray analysis instrument, the collimator mechanism comprises means for gradual movement of the aperture window in two independent directions transversely to the X-ray beam, and the respective path of movement of the aperture window, which is accessible by the collimator mechanism, in each one of the independent directions is at least twice as large as the extension of the X-ray beam at the location of the aperture window in the respective independent direction.
The collimator mechanism of the design having two independent directions of movement (adjustment possibilities) offers an even greater, almost arbitrary selection of a coherent partial area of the cross-section of an X-ray beam. Towards this end, the aperture opening, which is at least as large as the extension of the X-ray beam, is made to overlap the X-ray beam only to such an extent as is required for the cross-section of the X-ray beam in the subsequent X-ray experiment (typically irradiation of a sample).
For this reason, only part of the aperture opening is penetrated by X-ray radiation in most positions of the aperture window and the remaining part of the aperture opening is not illuminated. The aperture window has a collimating frame of sufficient width around the aperture opening, which completely collimates that part of the X-ray radiation that does not pass the aperture opening.
In a centered (or completely opened) position of movement of the aperture window, the entire X-ray beam can pass through the aperture window, since the aperture opening (if necessary after corresponding adjustment of the window size in case it can be adjusted) is larger than or at least as large as the extension of the X-ray beam at the location of the aperture window.
The path of movement of the aperture window in the embodiment with two independent directions of movement is sufficiently large such that any point on the edge of the aperture collimator can be made to overlap any point on the edge of the cross-section of the X-ray beam (at the location of the aperture window). For this reason, a partial area of the cross-section of the X-ray beam can be selected from any direction. In accordance with the invention, at least VW>=2*RS applies for the two independent directions, with VW: path of movement of the aperture window, and RS: extension of the X-ray beam. In case the aperture opening is larger than the X-ray beam, VW>=AOE+RS preferably also applies for any of the independent spatial directions, with AOE: extension of the aperture opening.
Due to the gradually movable collimator mechanism, the area of the selected (transmitted) partial area of the X-ray beam cross-section can also be gradually selected. In accordance with the invention, this partial area may be selected to have any area portion of between 0% and 100% of the X-ray beam cross-section. It should be noted that the aperture opening can be maintained at a fixed invariable value while the partial area is gradually selected.
A defined partial area of an X-ray beam is selected in accordance with the invention, in particular, in order to improve the data quality of an X-ray diffractive measurement, in particular, a signal-to-noise ratio. The selection of an optimum partial area can be determined, in particular, by means of ray tracing methods, thereby taking into consideration the properties of the (multi-layer) X-ray optics in a simulation, in particular, wherein the distribution of the X-ray flux density over the cross-section of the X-ray beam is calculated, and the effects of selection of different partial areas of the cross-section on the intensity distribution in a detection plane are determined.
The at least one direction or the two independent directions are preferably at least approximately perpendicular with respect to the direction of propagation of the X-ray beam. The two independent directions are moreover preferably at least approximately perpendicular with respect to each other. The “location of the aperture window” relates to the position with respect to the direction of propagation of the X-ray beam.
In a preferred embodiment of the inventive X-ray analysis instrument, the size of the aperture opening cannot be adjusted. An aperture window with fixed aperture opening has a particularly simple and therefore inexpensive construction.
In an alternative advantageous embodiment of the collimator mechanism, the size of the aperture opening can be adjusted, wherein the aperture opening can be adjusted to a size that is at least as large as the cross-section of the X-ray beam at the location of the aperture window. Other selectable sizes of the aperture window are then typically smaller than the cross-section of the X-ray beam. This embodiment offers even greater freedom with respect to selection of the partial area of the X-ray beam cross-section. In particular, it is possible to select partial areas inside the cross-section (i.e. partial areas without edge portion).
In a preferred further development of this embodiment, the collimator mechanism has two oppositely movable L-shaped aperture sections for adjusting the size of the aperture opening. This simple structure has proven to be useful in practice.
In one further preferred embodiment of the inventive. X-ray analysis instrument, the collimator mechanism is disposed on the output side of the X-ray optics. This obtains optimum control of the beam geometry, in particular the beam convergence, on an illuminated sample.
In one particularly preferred embodiment, the aperture window has a square aperture opening, the X-ray beam has an approximately square cross-section at the location of the aperture collimator, wherein the side edges of the square aperture opening and the square cross-section of the X-ray are oriented parallel to each other and the at least one direction in which the aperture window can be moved is oriented along a diagonal of the square aperture opening. In this case, a square partial area of the X-ray beam can be effectively varied in size through movement along only one diagonal. The beam quality also often varies greatly in the direction of the corner areas of a square X-ray beam cross-section, and the above-mentioned arrangement of the paths of movement particularly facilitates access to these corner areas. The at least one direction preferably extends along the diagonal of the X-ray beam cross-section, which maps the portion of the X-ray beam near to the source into that portion remote from the source. When two independent directions of movement are provided, these typically extend along the two diagonals of the square X-ray beam cross-section.
Another preferred embodiment is characterized in that the X-ray optics is disposed in a gas-tight optical housing and the collimator mechanism is disposed in a gas-tight collimator housing, wherein the two housings are evacuated or flooded with a protective gas, or the X-ray optics and the collimator mechanism are disposed in a common gas-tight housing, wherein the common housing is evacuated or flooded with a protective gas. In both cases, the protective gas reduces corrosion and soiling of the surfaces of the X-ray optics and the collimator mechanism as well as air absorption.
In another advantageous embodiment, the means for gradual movement of the aperture window comprise at least one micrometer screw and/or at least one fine thread bolt. These means have proven to be useful in practice. The micrometer screw is particularly advantageous for frequent adjustment of the direction.
In another advantageous embodiment, the collimator mechanism has a holder for an exchangeable aperture window element and the holder can be moved by the means for gradual movement of the aperture window. For this reason, the X-ray analysis means can be easily adjusted to different requirements, in particular spatial extensions of the X-ray beam.
An inventive X-ray analysis instrument can be used, in particular, in X-ray diffractometry to select a part of the X-ray beam by means of the aperture opening of the aperture window and direct it onto a sample in order to improve the reflex separation. The inventive X-ray analysis means permits selection of the portion (or partial area) in a specific and thereby particularly simple and flexible fashion.
The present invention also concerns the application of a collimator mechanism, comprising an aperture window with an aperture opening for selecting a portion of an X-ray beam, wherein the X-ray beam is emitted by an X-ray source and is imaged onto a sample by an X-ray optics, in particular, a multi-layer X-ray mirror, in particular, wherein this application is performed with an inventive X-ray analysis instrument, characterized in that a portion of the X-ray beam on the X-ray optics, which is remote from the source, is selected for adjusting, in particular, reducing the focus size of the X-ray beam at the location of the sample by means of the aperture opening of the aperture window. In accordance with the invention, it has turned out that a portion of an X-ray beam that is remote from the source can yield better data quality, in particular, an improved signal-to-background ratio in X-ray experiments, in particular in X-ray diffraction experiments, on samples that are smaller compared to the overall X-ray beam at the sample location. In particular, scattering on air, on the sample holder or other parts of the X-ray analysis instrument can be reduced by optimizing the focus size. In case of single reflection on the X-ray optics (e.g. a Goebel mirror), the cross-sectional area of the selected portion of the X-ray beam that is remote from the source extends at the location of the aperture window maximally to the center line of the cross-section of the overall X-ray beam in accordance with the invention, wherein this center line divides the X-ray beam at the location of the aperture window into one half close to the source and one half remote from the source (with respect to reflection on the X-ray optics) with respectively identical area portions. In case of double reflection on the X-ray optics (e.g. Montel optics) in accordance with the invention, the selected portion of the X-ray beam that is remote from the source extends maximally to the two center lines of the cross-section of the overall X-ray beam, wherein these center lines divide the X-ray beam at the location of the aperture window, in each case, into one half close to the source and one half remote from the source (with respect to the respective reflection on the X-ray optics) with respectively identical area portions. In other words, the selected portion of the X-ray beam remote from the source then lies in that surface area (typically “quarter”) of the X-ray cross-section, with respect to which both reflections on the X-ray optics are to be attributed to the side remote from the source. The portion of the X-ray remote from the source comprises 50% or less, preferably 40% or less of the cross-sectional area of the entire X-ray beam in case of single reflection. In case of double reflection, the portion of the X-ray beam remote from the source typically comprises 25% or less and preferably 20% or less of the cross-sectional area of the entire X-ray beam.
In one preferred variant of the inventive use, the focus size of the X-ray beam is adjusted to the size of the sample at the location of the sample. The signal-to-background ratio can be optimized through (if possible) complete illumination of the sample, i.e. only of the sample. The focus size is adjusted, in particular, through relative positioning of the aperture opening with respect to the X-ray in view of closeness or remoteness with respect to the source (i.e. transversely to the direction of propagation of the X-ray), whereby the focus size at the sample location can also be adjusted when the size of the aperture opening is invariable or when the area of the selected beam cross-section is the same.
In one advantageous variant of the inventive use, the selected portion of the X-ray beam remote from the source has a below-average mean photon flux density compared to the remaining X-ray beam. The reflex separation or the signal-to-background ratio can sometimes be surprisingly improved although the mean flux density in the selected portion is smaller than in the remaining (or also in the entire) X-ray beam compared e.g. to the use of a portion close to the source having a constantly larger mean flux density than the remaining (or also the entire) X-ray beam. The mean flux density in a selected portion of the X-ray beam is determined via the overall (integrated) photon flux in the selected portion divided by the cross-sectional area of the selected portion. The same applies for the remaining X-ray beam.
In another preferred variant of use, the aperture window is positioned in such a fashion that X-ray radiation does not pass through one part of the aperture opening of the aperture window. In other words, only one part of the aperture opening is held into the X-ray beam (or made to overlap the X-ray beam). It is thereby possible to easily select a portion of an X-ray beam cross-section for transmission, which is smaller than the aperture opening, even when the aperture opening is large.
Finally, in a preferred variant of use, the aperture window is disposed in the X-ray beam between the X-ray optics and the sample. This, in turn, realizes good control of the beam geometry, in particular the beam convergence on the illuminated sample.
Further advantages of the invention can be extracted from the description and the drawing. The features mentioned above and below may be used in accordance with the invention either individually or collectively in arbitrary combination. The embodiments shown and described are not to be understood as exhaustive enumeration but have exemplary character for describing the invention.
The invention is illustrated in the drawing and is explained in more detail with respect to embodiments.
a, 15b show schematic top views of a collimator mechanism with adjustable aperture opening size for the invention, with two different adjusted window sizes;
a-17b show experimentally determined diffraction patterns of a small thaumatin crystal with a beam having a focus size of 0.25 mm at the location of the sample (
a shows a schematic view of an inventive X-ray analysis instrument;
b shows a schematic cross-sectional view of
a-19c show schematic views of different positions of movement of an aperture window relative to an X-ray beam for illustrating the inventive paths of movement of the aperture window.
The invention concerns an X-ray analysis instrument, in particular, an X-ray diffractometer, with an X-ray source, an X-ray optics, in particular, a multi-layer X-ray mirror, and a variable collimator mechanism.
Multi-layer X-ray optics and their applications in X-ray diffractometry are disclosed e.g. in U.S. Pat. No. 6,226,349 for so-called Goebel mirrors and in U.S. Pat. No. 6,041,099 for Montel mirrors (also called Montel optics). These multi-layer X-ray mirrors use artificially generated multi-layer systems in order to monochromatize and parallelize or focus X-rays for X-ray analytical applications. A parabolically shaped mirror generates a parallel beam and an elliptically shaped mirror generates a focussed beam. The layer period (“d-spacing”) of the multi-layers must vary along the mirror in order to meet the Bragg relationship for one single wavelength (e.g. Cu—K-alpha radiation) at any position of the mirror. The mathematical dependence of this layer thickness variation is disclosed in earlier documents (laterally d-spacing graded multilayers, see e.g. M. Schuster et al., Proc. SPIE 3767, 1999, pages 183-198).
Montel optics substantially consist of two Goebel mirrors which are disposed perpendicularly with respect to each other. While Goebel mirrors parallelize or focus the X-ray only in one dimension, Montel mirrors parallelize or focus in two dimensions.
One disadvantage of these X-ray mirrors is that the beam properties on the output side of the mirrors are determined by the design of the optics. In the production e.g. of a focussing Goebel mirror, the physical values such as output convergence, focal lengths between the source and image focus, enlargement and thereby the size of the X-ray in the image focus must be determined prior to production. The values f1, f2, a, b, θ, L, must be fixedly determined prior to production and cannot be varied at a later time. When the requirements are changed, a new mirror type must be produced, which is complex and expensive. For this reason, it cannot be flexibly used for different sample requirements. Other sample requirements must be considered under suboptimal conditions or the optics must be changed, which is expensive and requires considerable modification and complex adjustment of the system. Later bending of the mirror into a different shape is not feasible, since the coating would also have to be changed to meet the Bragg condition, which is generally not possible at a later time.
One substantial beam property is the convergence β, since the resolution of the diffractometer decreases with increasing β. The separation of closely neighboring diffraction reflexes of the sample requires that β is not excessively large. If the sample requires a higher resolution, the mirror must be changed.
Exchangeable apertures (see U.S. Pat. No. 7,386,097) or an adjustable convergence collimator (see U.S. Pat. No. 7,245,699 B2) were therefore proposed for adjustment to changing measurement requirements. U.S. Pat. No. 7,386,097 substantially describes a Nipkow disc or alternatively movable bands. The production of these components having the required quality is difficult and their structural dimensions are relatively large. Integration in the beam path, that can usually be evacuated in order to protect the optics, or can be flushed with inert protective gas, does not seem to be possible. In U.S. Pat. No. 7,245,699B2, the aperture always consists of a stationary and a movable part. In the design of U.S. Pat. No. 7,245,699 B2, the movable part always only blocks the part of the radiation reflected by the optics, which is remote from the source. In accordance with U.S. Pat. No. 7,245,699 B2, this portion is less efficient than the portion close to the source.
In the above-mentioned conventional devices for limiting the divergence, the beam conditioning possibilities are greatly limited. The aperture disclosed in U.S. Pat. No. 7,245,699 B2 consists of one stationary and one movable component. In particular, it can collimate out only the part of the radiation that is remote from the source. With respect to the alternating apertures in accordance with U.S. Pat. No. 7,386,097, the beam divergence can only be adjusted in steps and not continuously.
It is the underlying purpose of the present invention to increase the field of use of X-ray optics by using an improved very compact collimator mechanism and thereby improve the data quality of X-ray diffractometers in general.
The present invention proposes an X-ray analysis instrument, in particular, an X-ray diffractometer, comprising an X-ray optics and a collimator mechanism that consists of one or more apertures that can all be gradually moved in at least one direction and preferably in two independent directions perpendicularly to the optical axis, and the paths of movement of which are at least twice as large as the X-ray beam emitted from the X-ray optics such that any feasible portion of the X-ray beam emitted from the X-ray optics can be used to illuminate the sample. The collimator mechanism preferably has at least one completely opened position. The collimator mechanism is preferably mounted on the output side of the X-ray optics.
The inventive construction is easy to operate compared to prior art, has a compact construction and is therefore inexpensive to produce but offers substantial flexibility with regard to the field of use of X-ray optics and also extremely simple and reproducible handling. It can even be completely integrated in existing optical housings that can be evacuated e.g. in correspondence with U.S. Pat. No. 7,511,902. This is explained in more detail below.
A ray tracing program that was optimized for X-ray optics was developed in accordance with the present invention. Comparisons with experiments showed that this ray tracing program produces excellent exact predictions. The inventors found out through such ray tracing calculations that the beam profile on the output side of typical X-ray mirrors is often not homogeneous with respect to intensity.
On the basis of
The following illustrations show that for ray tracing calculations a square collimator (aperture window 2) (sketched in
These results show that different directions of movement of the collimator change the beam properties in different ways and thereby increase the flexibility for optimizing the beam properties with changing measurement requirements.
In addition to the illustrated directions of movement A and B diagonally through the square beam, other beam cross-sections, directions of movement (or pairs of directions of movement) and positionings of the collimator are clearly also possible.
A collimator mechanism BM that is constructed on the basis of calculations (see
The movement of the collimator in the X and Y directions could also be realized through other adjustment mechanisms e.g. via two micrometer screws, two simple adjusting screws, elongated holes with screws etc. An embodiment with only one micrometer screw and one fine thread bolt is advantageous when the collimator is to be adjusted only once in height with respect to a square beam, standing on edge, while the adjustment for collimating out undesired beam portions is mainly performed in a horizontal direction.
In order to ensure optimum collimator size and shape, the collimator may be designed to be exchangeable (see
Collimators with holes (aperture openings 3) of different shapes such as rectangles, diamonds, squares or circles can be used within the scope of the present invention. One preferred structural shape utilizes a square standing on edge. One further structural type is the rectangular collimator shown in
The collimator housing 1 can be mounted either in front of or behind an optical housing 17 e.g. in correspondence with DE 10 2006 015933 B3 (see
The operating direction of the micrometer screw 5 can be changed by mounting the adjustment mechanism in a different orientation and mounting the micrometer screw 5 on the opposite side. In practice, this facilitates the use in left-hand and right-hand side system solutions. In order to be able to further operate the housing 1 under vacuum, the hole that is not used by the micrometer screw is provided with a blind plug 8.
A crystal of a defined size and known lattice constants was mounted on an X-ray diffractometer (Smart Apex-II, Bruker AXS) at a fixed separation from the source and detector. The crystal had a long cell axis that showed a tendency for reflex superpositions with the selected detector separation. The crystal was oriented in such a fashion that the closely neighboring reflexes of the long cell axis on the detector were easily recognizable.
Several scans with completely opened aperture were performed and evaluated as a reference measurement. The overall flux of the source with opened aperture was measured with a photo diode and recorded. Then, the scans were repeated on the same crystal with the collimator being adjusted to half flux, and evaluated in the same fashion. The aperture was initially used to collimate out to half the flux in the direction of movement A (setting 1). The evaluation of the measured scans showed that the average normalized diffracted intensity was reduced to 33%. The ratio between signal and background was reduced to just under 60%. Then, the aperture was used to collimate out to half the flux in the direction of movement B (setting 2). The evaluation of the scans showed that the average normalized diffracted intensity with setting 2 was reduced to 45% and the ratio between signal and background to 74%. Setting 2 therefore yielded better results than setting 1.
By moving the collimator to positions with reduced flux, reflex separation was advantageously further improved. The evaluation included more reflexes compared to completely opened collimator as is shown in table 1. This result coincided in terms of quality with the predictions of the ray tracing calculations which did not contain any sample-specific properties such as the mosaicity of the crystal. The effect of improved reflex separation is indeed not dramatic in this example of application, but becomes greater with reduced detector separation or with samples having even longer cell axes, for determining the structure.
In total, setting 2 (direction of movement B) yielded better results in contrast to prior art according to U.S. Pat. No. 7,245,699 B2. In accordance with a device of U.S. Pat. No. 7,245,699 B2, this beam portion is not accessible. The beam portion that is described as being less efficient in accordance with U.S. Pat. No. 7,245,699 B2 obviously surprisingly yields a better signal-to-noise ratio.
a and 17b show two diffraction patterns on a small thaumatin crystal, one with a beam having a size of approximately 0.25 mm (
Such a change of the focus size previously required a change of the optics. This is now realized by the inventive collimator mechanism in a very simple and inexpensive fashion without changing the optics. In accordance with U.S. Pat. No. 7,245,699 B2, only the path of movement B is possible which always results in beam enlargement. This is, however, unfavorable for small samples as is shown in the experimental results of
a schematically shows an inventive X-ray analysis instrument, in the present case an X-ray diffractometer 21. An X-ray beam 23 is emitted from an X-ray source 22, which is reflected and thereby focused by an X-ray optics 24, in the present case a Goebel mirror. An aperture window 2 with an aperture opening 3 is disposed in the X-ray beam 23 on the output side of the Goebel mirror. The aperture window 2 is part of a collimator mechanism and can be gradually moved perpendicularly to the direction of propagation of the X-ray beam 23 in two independent directions x and y. It should be noted that the y direction extends perpendicularly to the plane of the drawing, and the z direction extends parallel to the direction of propagation of the X-ray radiation in the area of the aperture window 2. The collimator mechanism has means for gradual movement of the aperture window 2, which are not shown in detail, e.g. a micrometer screw or a fine thread bolt.
The X-ray beam 23 has an extension RSx in the x direction at the location (with respect to the z direction) of the aperture window 2, and the aperture opening 2 has an extension AOEx in the x direction. In accordance with the invention RSx<=AOEx (in the illustrated embodiment RSx is slightly smaller than AOEx). The same applies for the corresponding values in the y direction.
In the illustrated situation, the aperture window 2 is used to permit passage of a first partial area of the X-ray 23, i.e. in
Only the partial beam 26 reaches the sample 27 to interact with it. The radiation that was diffracted by the sample 27 can be detected by means of a detector 28. In the present case, the detector 28 can be moved around the sample 27 along a circular arc.
b shows the relationships in the cross-section 32 of the X-ray beam at the location (i.e. the z position) of the aperture window of
In
a through 19c illustrate the inventive movability of an aperture window 2 in a plane perpendicular to the direction of propagation (in the present case the z direction) of an X-ray beam, typically on the output side of (behind) a multi-layer X-ray optics. In the illustrated example, the aperture window 2 can be moved in two independent (in the present case also orthogonal) directions x and y in each case over a path of movement that corresponds to twice the extension of the X-ray beam cross-section in the respective direction. In accordance with the invention, only one direction of movement may be provided (e.g. only the illustrated possible movement in the x direction), or the movability in a second direction (e.g. the y direction) can be reduced to a path of movement that is smaller than twice the extension of the X-ray beam in the second direction and only be used for fine adjustment of the aperture window.
a initially shows a completely opened (centered) position of movement of the aperture window 2. The aperture window 2 comprises a collimating frame 31 and (in the present case) a rectangular aperture opening 3. The aperture opening 3 has the extension AOEx in the x direction and the extension AOEy in the y direction. In the illustrated embodiment, the X-ray beam has an oval cross-section 32 with an extension RSx in the x direction and RSy in the y direction at the location of the aperture window 2 (non-shaded).
In accordance with the present invention, the aperture opening 3 is at least as large as the cross-section 32 of the X-ray beam, i.e. the cross-section 32 of the X-ray beam is (in the completely opened position) completely within the aperture opening 3. In the illustrated embodiment, the following exactly applies: RSx=AOEx and RSy=AOEy. In accordance with the invention, RSx<AOEx and/or RSy<AOEy may also be established.
b illustrates the movability of the aperture window 2 in the x direction. The aperture window 2 can be shifted in the positive x direction at least to such an extent that the aperture opening 3 just ceases to overlap the cross-section 32 of the X-ray beam. The same applies in the negative x direction (see dashed aperture window 2′ with aperture opening 3′). Towards this end, the path of movement VWx of the aperture window 2 (illustrated for the lower edge of the aperture opening 3) in the x direction in the illustrated embodiment is at least twice as large as the extension RSx of the X-ray beam in the x direction. With RSx<AOEx, a path of movement VWx>=RSx+AOEx must be established in order to be able to move the aperture window 2 out of the X-ray beam both in the positive and negative x direction in accordance with the invention.
c shows the movability of the aperture window 2 in the y direction. The aperture window 2 can be moved again in the positive y direction at least to such an extent that the aperture opening 3 just ceases to overlap the cross-section 32 of the X-ray beam. The same applies in the negative y direction (see dashed aperture window 2′ with aperture opening 3′). Towards this end, the path of movement VWy of the aperture window 2 (illustrated for the left-hand edge of the aperture opening 3) in the y direction in the illustrated embodiment is at least twice as large as the extension RSy of the X-ray beam in the y direction. In case of RSy<AOEy, a path of movement VWy>=RSy+AOEy must be provided in order to be able to move the aperture window 2 out of the X-ray beam both in the positive and negative y direction in accordance with the invention.
Since the aperture opening 3 can at least be moved just out of the cross-section 32 of the X-ray beam in the two independent spatial directions x and y, an edge partial area of the cross-section 32 can be selected from each direction of approach for overlapping with the aperture opening 3 and be supplied to a subsequent X-ray experiment. The remaining partial area of the cross-section 32 is then blocked by the collimating frame 31. The area portion of the selected partial area can be gradually selected due to the gradual movability of the aperture window 2 in both directions x and y, in particular, in order to optimize the photon flux, photon flux density and/or beam divergence in the subsequent X-ray analysis experiment. The overall X-ray beam can additionally be passed to the subsequent experiment in the completely opened position of movement of the aperture window 2. The size of the aperture opening of the aperture window can optionally also be adjusted by the collimator mechanism, in particular reduced, preferably gradually reduced such that non-edge partial areas of the cross-section of the X-ray can also be selected (see in this connection also
The present invention provides optimum freedom for the selection of a partial area of an X-ray beam cross-section for an X-ray analysis experiment.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2008 050 851.9 | Oct 2008 | DE | national |
| 09 000 179.3 | Jan 2009 | EP | regional |
