Method and apparatus for analysis of samples

A method and a device examine a sample with radiation emitted from a radiation source, which is directed to the sample carried by a sample holder via a beamforming unit and detected by a detector and evaluated in an evaluating unit. Prior to the examination of the sample, at least one of the following components, including the radiation source, beamforming unit, sample holder, detector, and a primary beam stop, are spatially oriented and/or positioned in relation to at least one of the other components and/or in relation to a predefined fixed point and/or in relation to the optical path with a control unit via actuating drives. The radiation intensity measured by the detector, in a predefined detector range, and/or a value derived therefrom is used for establishing a control variable conferred from the control unit to the actuating drives assigned to the components.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority, under 35 U.S.C.§119(e), of Austrian provisional application No. AT50552/2012, filed Nov. 30, 2012; the prior application is herewith incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a method and a device for examining a sample with radiation emitted from a neutron or X-ray radiation source, directed to the sample carried by a sample holder via at least one beam-forming unit, preferably beam-forming optics and/or beam-limiting optics, detected by a detector and evaluated in an evaluating unit.

The elastic scattering of X-ray radiation is used for non-destructive characterization of the structure of various sample materials. This kind of scattering-angle measurement can be conducted by X-ray radiation as well as, in a comparable manner, by neutron radiation. The invention can be implemented using both kinds of radiation.

X-ray scattering occurs when a beam of X-ray radiation impinges on an inhomogeneous, powdery, liquid, and/or solid material having a structure which is larger than the wavelength of the X-ray radiation employed. The X-rays penetrate into the sample, and the material being studied interacts with the X-ray beam, resulting in scattering. This results in characteristic interference images; the sum of waves scattered under a certain angle is characteristic of the size and symmetry of the scattering particles.

In principle, two different scattering geometries can be employed for small-angle scattering. Either the samples are positioned at a small angle with respect to the measurement beam, the measurement being performed at a grazing incidence close to the critical angle of total reflection and the pattern of the scattered radiation being recorded, or the sample is positioned so as to have the beam transmitted through it. With the first method, information is obtained about the surface structure of the sample, while with transmission scattering the nanostructure of the overall sample volume is analyzed.

Measurement devices of known and inventive kinds typically contain a neutron or X-ray source with adequate optics. As beam-generating sources, for example, stationary X-ray tubes, rotating anodes or a synchrotron can be used. For focusing or forming the beam and for monochromatization, for example, one-dimensional optics, such as Goebel mirror, or two-dimensional arrangements, such as those according to Kirkpatrick-Baez, are used. Convergent, focused, slightly diverging and parallelized bundles of rays can all be used for measurement. The focus of the measurement radiation can be in the plane of the sample to be examined or in the detector plane.

The measurement beam can be additionally shaped and/or masked out using an arrangement of apertures/diaphragms and/or a collimation system in order to send a parallel bundle of measurement beams as free of interfering scattering portions as possible for examination onto the sample to be examined. After interacting with the sample, the scattering image is measured using an X-ray detector, and the measured intensities are delivered to an evaluating unit. As only a small part of the measurement beam impinging on the sample is scattered, the unscattered portion of the measurement radiation, i.e. the primary beam, is masked out from the detector using a primary beam stop in order not to damage the detector.

Actual aberrations from an ideal scattering experiment are corrected using different mathematical corrections each applicable for the beam shape and scattering geometry selected.

One-dimensional detectors such as photo diode arrays, which detect the intensity distribution in a line perpendicular to the primary beam can be used as well as 2-dimensional arrangements such as CCD cameras, image plates or X-ray films.

FIG. 1shows the basic design of small-angle scattering measurements based on a known classic Kratky camera, as described, for example, in German patent DE 1002138 B1 (corresponding to U.S. Pat. No. 6,881,537). The radiation emitted from a radiation source0is focused in subsequent optics1onto a sample3or a detector5, which is positioned at a distance S from the sample3carried by a sample holder7and has an evaluating unit30connected thereto. There is a primary beam stop4in front of the detector5. Slightly diverging beams can also be used, as the angle of aperture is small and sufficient intensities are available after beam limitation. Due to constantly present roughness's of the optics used and to construction tolerances, the bundle of beams thus obtained is usually additionally limited after the optics and optionally collimated in a collimator2. Diaphragms used for finely masking out X-rays always emit scattering radiation themselves, which becomes very intense especially under small angles. For this reason, a number or combination of diaphragms successive in the optical path are usually used. For example, a slit collimator can be used as a combination of diaphragms, which contains two blocks for masking out and collimating the measurement beam.

When examining samples, the intensity of measurement radiation directed to the sample should be as high as possible. In order to achieve this, however, the resolution towards small angles required for each individual measurement problem needs to be taken into account. Apart from production tolerances of individual components like collimation block, diaphragms, beam optics, etc., the focused X-rays emitted by the source will also change due to characteristics of the sources and the components that are subject to change by time, such as temperature influences and aging phenomena. In addition, in a modular system, the change of individual components, such as source, beam optics, sample holders, etc., requires adjustments, which need to be able to be made as quickly and as comfortably for the operator as possible.

Mechanisms for adjusting the components are known in prior art. For example, German patent DE 103 17 677 (corresponding to U.S. Pat. No. 7,295,650) illustrates adjustment of the primary beam stop in z-direction using mechanical devices. Adjustments can be made using manually operated mechanical precision regulators or micrometer screws as well as via spindle drives and electrical stepper motors.

In order to protect the sensitive detector, the radiation intensity emitted from the source can be reduced upon adjustment of the system. If reduction of the intensity emitted from the source that is used is either not desired or not possible, reduction can be done by an absorber inserted between the source and the beam-focusing optics. If sensitive detectors are used, the memory map of which is available only by separate reading, such as image plates, or if the radiation of the sources is not supposed to be modified in its intensity, a support detector can be used alternatively in the place or in front of the detector, for which photo diodes, X-ray films or X-ray fluorescent screens find use, for example.

At present, a user will, prior to measurement or in between consecutive measurements, adjust the individual components of a device manually in a predefined sequence for adequate intensity on detector plane and, to do so, read the intensities measured at the detector in the course of change and/or at every adjustment step. These adjustment steps are described to the user in the manual including the required position of the image and/or intensities of primary beams and/or scattering images at the detector. This adjustment procedure thus requires a highly trained and experienced user, who makes all necessary adjustments manually with sure instincts and coordinates the individual components such that an optimal adjustment result is achieved with respect to the following measurement. This procedure is lengthy and error-prone, the individual components may even be destroyed due to faulty adjustment, and X-rays can exit from the device into the environment in the case of faulty adjustments.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide a method and an apparatus for analysis of samples that overcome the above-mentioned disadvantages of the prior art devices and methods of this general type.

These problems are solved according to the invention in a method of the above kind by orienting and/or adjusting with respect to its/their position in space at least one, preferably several, in particular all, of the following components in relation to at least one of the other components and/or in relation to a predefined fixed point and/or in relation to the optical path with a control unit via actuating drives prior to examining the sample: radiation source and/or beam-forming unit and/or sample holder and/or detector and/or optionally a primary beam stop upstream of the detector. The radiation intensity measured by the detector, in particular in at least one predefined detector range, and/or a value derived therefrom is used for creating a control variable sent from the control unit to the control circuits of the actuating drives assigned to each individual component.

Using the inventive procedure it is possible to perform adjustment of the device quickly and accurately, optionally following a dictated protocol, and to initialize and/or prepare a subsequent examination with high accuracy. According to the invention, adjustment of the inventive device becomes easy to handle for the user, particularly if the entire adjustment process is carried out in an automated manner via control circuits and controllable components. To achieve that, the intensity occurring at the detector and/or determined using the intended evaluating unit and/or values associated therewith and/or derived therefrom are used as control variable for the individual components of the device.

To achieve that, a plurality, or preferably all, of the adjustable components are each equipped with at least one controllable actuating drive. The actuating drives communicate with the control unit connected to the detector and/or the evaluating unit and are preferably controlled via the control variables “intensity at the detector” and/or “position of the image at the detector”.

According to the invention, the individual components can each by adjusted automatically according to an adjustment program included in the control and/or evaluating units, with the entire adjustment procedure being advantageously carried out step by step automatically for each individual component.

Even when only one of the components of the inventive device is adjusted using the intended control unit, facilitation and specification of the adjustment process will occur. The radiation intensity used as a control variable reacts very sensitively to non-exact adjustment, hence it is possible to quickly obtain an optimum value for proper and/or required adjustment of the respective component. Adjustment of one or more components can be carried out in a predefined sequence of adjustment steps or in accord with the problem in question.

It is of advantage that no adjustment steps and/or settings that are dependent on the user are required. Thanks to automatic adjustment, absolute positions or adjustment intensities can be reconstituted in a reproducible manner; this guarantees comparability of measurements in the case of serial examinations, for example, of nanoparticles.

It is of advantage if the individual components are adjusted, optionally independently, to a predefined starting position before conducting a measurement, or if they are in a defined starting position, while those values of this starting adjustment that correspond to the position and/or orientation of each component are used as starting values for adjustment.

The initial settings of the adjustment process are thus clearly defined, serving as the basis for the following special adjustment.

It is useful to compare the radiation intensity determined at the detector and/or values derived therefrom with saved set values and to adjust the individual components with the actuating drives based on this comparison and/or to approximate the radiation intensity measured in the at least one predefined detector range to a predefined value, in particular a maximum value, during adjustment of the individual components and/or to determine and/or use the signal/noise ratio and/or the absolute intensity in the integral, two-dimensional image at the detector and/or the intensity of single intensity maximums in the scattering image and/or, especially when using a one-dimensional detector that is moved over the measured angular range, local intensity maximums as the values derived from the measured radiation intensity.

The measured intensities or any values derived therefrom can directly be used for determining the control variables for the actuating drives, as long as these values have significant dependency on the respective position and/or orientation of the respective component.

In order to obtain maximum variety of readjustment options for adjustment and to take all types of adjustable components into account, it can be intended to readjust the components in the direction of the optical path and/or in a plane perpendicular thereto and/or for adjustment in terms of their position in space and/or to readjust them in their orientation in terms of the axis of the optical path and/or to twist them, in particular around the axis of the optical path, and/or to tilt them with respect to that axis.

In order to increase the precision of adjustment, it can be intended to measure the X-rays impinging on the detector for determining the control variables in a variety of detector ranges, while optionally the course of radiation intensity is integrated over predefined detector ranges.

According to the invention, a device of the kind mentioned above is characterized in that at least one component, preferably a number of components or each of the components, including radiation source and/or beam-forming unit and/or beam-limiting unit and/or sample holder and/or detector and/or optionally a primary beam stop upstream of the detector, is connected and readjustable with at least one, in particular to at least one individual, actuating drive, which can be supplied with actuating signals from a control unit. The control unit has an input for measured values of radiation intensities determined in at least one predefined detector range of the detector and/or values derived therefrom and produces the actuating signals based on these measured values.

The design of the device allows for quick, accurate and safe adjustment of the components. By dictated protocols, faulty adjustments can be excluded from the beginning. For safety reasons, predefined limits can be set to the adjustment moves of the actuating drives. It is possible to adjust the individual components independently and accurately step by step and/or in a predefined sequence.

Simple and quick adjustment of the device is accomplished when the control unit has an input for the respective adjustment values corresponding to the orientation and/or position of the components. These actual values either are present saved in memories or can be determined by measurement units connected to the control unit, or are provided and/or obtainable by the actuating drives and/or the control unit has a comparator, by which the measured values of the radiation intensity determined in the predefined detector ranges are comparable to actual adjustment values saved and/or determined for the individual components.

In connection with the components to be adjusted, it is of advantage if they are provided in a form adjustable to all spatial directions, and it is particularly useful for the beam-forming optics and/or the beam-limiting optics and the radiation source to be shiftable with respect to one another in the three spatial dimensions and/or rotatable around the optical axis and the optical path, respectively, and/or tiltably supported and readjustable in a driven manner.

Depending on type and design of the individual components, orientation and position play an important role, and it can be intended that, for adjusting the beam-forming and/or beam-shaping optics, these optics are provided in the form of diaphragms insertable and/or tiltable into the optical path or adjustable with respect to their gap width, and/or that the sample holder and/or the sample and/or the primary beam stops are carried by a carrier unit insertable into the optical path in a plane perpendicular to the optical path and/or tiltable into the optical path and/or that the mutual distance between the radiation source and the sample holder and/or the detector and/or the distance between the sample holder and the detector is adjustable using the actuating drives assigned to the respective components depending on the measured value of the radiation intensity and/or a value derived therefrom.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the figures of the drawings in detail and first, particularly toFIG. 2thereof, there is shown a basic design and the essential components of an inventive X-ray examination device which can be used to conduct the inventive method. The device is based on the device according toFIG. 1, supplemented by a control unit6, by which actuating drives11for individual components0,01,1,2,4,5,7can be controlled. Several actuating drives11can be attributed to each component, for example, to adjust the component to various directions in space. In a simple embodiment, the actuating drive11can adjust an arrangement movable along an x-y plane having a holder for the component to be adjusted.

When examining samples3, most of the time a maximum intensity of measurement radiation is supposed to be directed to the sample3, while the resolution for each individual measurement problem towards small angles has to be taken into consideration. Thus, the requirements placed in the adjustment are high. It is also important to determine the current position of the components. The current position of each component can be determined or obtained at any point in time by adequate position detection device, such as position sensors or the position of the actuating drives11per se, in particular if the actuating drives11report the position and/or orientation of the component back to the control unit6and/or the evaluating unit30. However, the determination of position can also be accomplished based on a resting position without absolute determination of the position, as it is the mutually relative position of the components that is relevant in this case.

Control of the actuating drives11is advantageously carried out by evaluating the intensity and/or intensity distribution recorded at the detector5, comparing the obtained intensity measurement value with a set value for optimum adjustment position, preferably within the evaluating unit30, and then moving the respective component. Appropriate control algorithms are predefined. The respective component is moved by the actuating drive11, until the intensity and/or intensity distribution measured at the detector5corresponds to the set value or approximates it as closely as possible.

As the detector5, a CCD array or a photodiode array or other position-sensitive detectors are preferably used, which support adjustment by recording images resolved according to their location, optionally in connection with image recognition software. A point-shaped detector that is being moved along the primary beam can also be used as the detector.

The method of adjusting the components in a small- and/or wide-angle measurement device advantageously begins after incorporating the desired components in a modular system or, in a stationary system without changing possibilities, by adjusting the radiation source0and the beam-forming optics1. Depending on the optics used, either the radiation source0and/or the beam-focusing optics1, such as mirrors, Goebel mirror, 2D optics, 3D optics, or the like, are oriented relative to one another, such that a primary beam with maximum intensity is created, which is then directed through the other components of this device. According to the invention, the first step can be automated by rotating and/or tilting the optics1or adjusting the radiation source0in the plane vertical to the z-axis of the device with the actuating drives11, at least when replacing the radiation source0and/or the focusing optics1. The z-axis is typically equal to the course of the optical path9. This step can be controlled using the control unit6. For adjusting the radiation source0and the beam-forming optics1, usually the collimating and/or beam-limiting optics2is removed. This is either done manually or by extending the beam-limiting optics2containing a collimator and diaphragms, the sample holder7, the primary beam stop4or, according to the invention, automatically by moving these components using the actuating drive11to a position which does not limit the measurement beam. To this end, usually an absorber01is used, which can also be brought into position by an actuating drive11.

When adjusting the beam-limiting optics2, such as slit collimators in the form of blocks or individual beam-limiting components, the primary beam stop4is moved from its measurement position using an actuating drive, and adjustment of the collimating element is done by tilting the same relative to the z-axis of the camera using the actuating drive11.

The diaphragm elements or collimation elements of the optics2can be arranged like the other components by mounting within a housing or on a holder and moved using actuating drives11, e.g. in the form of servomotors, linear motors and/or magnetic drives.

FIG. 3shows the arrangement of two collimation blocks B1and B2arranged on a carrier31and limiting the beam and a primary beam stop12. The members collimation blocks B1and B2and primary beam stop12can be taken together in a housing or frame to form a unit and/or to form the beam-limiting optics2and carried by the carrier31. This unit can be tilted relative to the optical axis during adjustment using the actuating drive11. This can either be done by tilting the entire optics2or by tilting a frame carrying the other components, radiation source0, the optics1, the beam stop4and the detector5, in which these components are arranged in a fixed manner along the optical axis9, i.e. in parallel to the z-direction, as what matters is merely the relative position and orientation of the individual components with respect to one another. Adjusting, as changing the diaphragm position, is done automatically using the actuating drives11operated by the control unit6.

FIG. 3Ashows beam-limiting optics2, containing two tiltable collimation blocks B1and B2as well as one adjustable inlet diaphragm32and adjustable outlet diaphragms7a,7b,7cand7d. Tilting and adjusting the diaphragms can be accomplished using the actuating drives11, which are indicated here like in the other figures.FIG. 3Bshows optics2, which are adjustable using servomotors11via spindle drives13a,13band13cin all spatial directions and tiltable around all spindle axes.

In order to achieve facilitated adjustment, optics2can be shifted along the y-axis using an actuating drive11to adapt the level of the diaphragm to the actual primary beam, while separately; a rotation around the z-axis can be accomplished using an actuating drive11to adjust the position of the collimated beam in the x-y plane. Adjustment of the adjustable elements of a collimation element can be accomplished by shifting the diaphragms using an actuating drive11along the x-axis as well as by adjusting the diaphragm gap.

As shown inFIG. 4, the diaphragms7aand7bof optics2can be movably mounted on a rail and/or holder in parallel to the x-direction. The actuating drives11can be used to change the distance between the diaphragms7aand7band thus also the gap width S1. The actuating drives11drive the spindles23aand23b, on which the two diaphragms7aand7bare mounted. In addition, the position of the gap can be shifted along the x-axis. This is done for adjusting the gap relative to the optical path9of the primary beam through the slit collimation blocks B1and B2. The collimation blocks B1, B2, and/or the entire beam-limiting optics can be adjusted by rotation around the z-axis and by rotation around the x-axis, each with specifically disposed servomotors11.

If, for example, adjustment is done using actuating drives11having stepper motors and spindle drives, the stepper motors can be driven by the evaluating unit30and/or the control unit6via control pulses, until the desired position is achieved for the diaphragms7a,7bwith respect to the slit collimation blocks B1and B2.

For example, the gap width S1can be calculated from the open or closed end position of the diaphragms7a,7bby counting the motor steps and known feed of the spindles23a,23bin the control unit6and/or the evaluating unit30. Alternatively, the distance between the two diaphragms7a,7bcan be determined using an appropriate length measurement system, such as an optical path sensor or a distance measuring device.

The position of the sample3, which is arranged on or accepted by any sample holder7, can be adjusted, for which first the sample holder7is placed in the position assigned for it. Various sample holders, such as changing cells, cuvettes, capillary holders, etc., can be provided. Sample holders7for measurements in a grazing incidence can also be used. Rotary movements, tiltings and grid movements can be conferred to the sample holder7, and thus the sample3, by actuating drives11relative to the optical path9in order to allow spatially resolved examinations.

A changing system can be provided for directing, fixing and incorporating the sample holder7, and it can have guiding pins, screwed joints and the like, which place the sample3in a predefined starting position with respect to the sample holder7.

Optionally the sample holder7can be equipped with a contactless sensor or chip, which optionally provides calibration data of the sample holder and can be recognized automatically. This data can be used as position and orientation measurement values in order to place each respective sample holder7that is movable in all directions in space and also arranged in a rotatable manner in the appropriate position using the actuating drives11.

FIG. 5shows such an arrangement with actuating drives11, which operate the respective spindles32a,32band32cfor translation of sample3in y-direction, translation in z-direction and translation in x-direction. At the same time tilting the sample holder7around the z-axis is possible using an actuating drive11. Controlling the movements of the actuating drives11can be done by a predefined number of steps with a pulse generator.

If a movable detector5is used in the system, the desired scattering angle range to be measured can optionally be accomplished by selecting the distance S between the sample3and the detector5. Setting the distance between the sample3and the detector5can be done by shifting the sample3and/or the sample holder7on a sample bench and/or shifting the detector5to the appropriate position automatically using the actuating drives11according to instructions. This way a fully automatic measurement with different angle ranges can be achieved by changing the distance between the sample3and the detector5and then evaluating the recorded spectra supported by automation and standardizing the measurements with respect to one another.

FIG. 6shows an adjustable sample holder7on a bench37movable in z-direction, in which the actuating drive11drives, a spindle36and thereby moves the sample bench37along the z-axis. Thus, the distance between the sample3and the detector5can be changed and the sample3shifted along the optical axis9. The sample bench37can be an integral part of the sample holder7or part of a removable sample changer. An entirely modular configuration is also possible.

The primary beam stop4has to be able to mask out a slit-shaped primary beam when the diaphragm gap is open. Primary beam stops4for a slit-collimated beam of varying line length and a point-collimated beam can be arranged interchangeably in a holder.

In order to fully automate the device, an automated change of different primary beam stops4,4′,4″ using a changing device15operated by the actuating drives11can be provided, i.e. the respective primary beam stop4is movable to and from the optical path9using an actuating drive11with a spindle drive36. Reference numeral18designates a rack of the device, which is able to support the components and actuating drives. Alternatively, a multipartite embodiment of the primary beam stop4can be implemented. In this case, at least one primary beam stop4is available for adjustment in a plane vertical to the optical path9. The beam stop4of choice is placed in its position in the measurement plane using the actuating drive11optionally from below and registered in y-direction with the measured intensity at the detector5by the primary beam. Optionally the orientation of the beam stop4has to be adapted with respect to the position of the gap at the detector5in the x-y plane by rotating around the z-axis using an actuating drive11. Preferably, the beam stop4is introduced to the optical path9from below in the x-y plane. Each primary beam stop4has a separate feed in y-direction as shown inFIG. 7for the primary beam stop4, which is adjustable using an actuating drive11with the spindle36.

The entire adjustment procedure can be automatic, for example, by selecting the control variable gradually or by defining absolute values. Control is done advantageously, for example, via “smallest detectable scattering angle” or “desired intensity at the detector” or a “desired” resolution.

A program present in the control unit6and/or in the evaluating unit30can also provide the user with fully defined measurement programs, e.g. for standard characterization of samples. The automated run of several different adjustment routines including measurement and subsequent joint evaluation of structural data, for example, of nanoparticles can span several orders of magnitude, as exemplified in detail as follows:

Selection of“Characterization of isotropicautomatic measurementnanoparticles with an anisotropicprograminternal crystalline structure”Adjustment routine 1Automatic moving of sample holder,adjustment of slit collimator and 2Doptics to maximum gap length andminimum height, automaticadjustment of primary beam stopMeasurement 1Acceptance of isotropic small-anglescattering with minimum qminAdjustment routine 2Adjustment of slit collimator and 2Doptics to minimum gap length(resolution of anisotropic structureand greater height), adjustment ofprimary beam stopMeasurement 2Acceptance of isotropic/anisotropicsmall-angle scatteringAdjustment routine 3Adjustment of slit collimator and 2Doptics, moving sample to largerdistanceMeasurement 3Acceptance of wide-angle scatteringEvaluation and illustration of theresults supported by automation

The zero positions from the adjustments can be deposited in the memory unit, such as the control unit6; they can be used to derive various measurement profiles.

The zero position and/or the starting values and the positions b for the various profiles in the program based on the automatic adjustment are saved, and during actual measurement of a sample when the threshold value is not reached, routines can proceed automatically. This can, for example, increase the measurement beam intensity and allow for an image that is better to evaluate. So it is possible, even in the case of differing samples without knowing the scattering intensities to be expected, to achieve an image that can be evaluated.

It is noted that units for determining the actual position and/or actual orientation of the individual components0,1,2,4,5,7are not depicted in the drawing. Respective measurement signals can be obtained by measurement devices of various kinds, which survey the components, or can be obtained via the actuating drives11per se, whose respective position can be regarded a measurement value relating to the position and/or orientation of the respective component.

As a point of reference for adjustment, the position of the radiation source0or the sample3can advantageously be used.