Simultaneous X-ray fluorescent spectrometer

The invention relates to a spectrometer for the simultaneous measurement several spectral lines of a test sample with a plurality Wavelength selectors, each light of a particular Wavelength selectively perform a detector, wherein in Typically, each wavelength selector selects a different wavelength.

Such a multi-channel spectrometer, for example, the Device "MRS 4000" Bruker AXS GmbH (see manual "Multichannel X-ray spectrometer MRS 4000" from years 1997).

To study the optical properties of test samples, in particular to determine the chemical composition due to the specific optical properties of the various Atoms and molecules is a wide variety of Spectrometer used, the wavelength ranges in from the far infrared through the visible region work up to the field of X-rays. Allen These spectrometers have in common that the to be examined betrahlt measuring sample with light of one or more wavelengths is either in transmission or in reflection the changed by the sample light, the properties of the the sample indicates is detected and spectrally analyzed.

To a spectral resolution of the detected measurement signals to obtained two alternative methods have hitherto been used, namely the use of an energy-dispersive arrangement or the use of a wavelength-dispersive Arrangement.

An energy dispersive spectrometer generally has only a single detector, the right of the sample originating takes to be examined radiation. Since the detector "Looks directly at the sample" he accepts not only the interest "Effective radiation" on, but he also sees the entire surface and EMI. Specifically, the Detector often strongly influenced by the radiation of the main elements the sample loaded, which are sometimes not analyzed are, because they are known already. This disappearing the signals of the really interesting elements in the high detected background or background signal. On Such energy dispersive spectrometer therefore has a small resolution and a high detection limit and is relatively inefficient.

Alternatively, wavelength dispersive spectrometer used, such as the above-cited multi-channel X-ray spectrometer "MRS 4000". These devices have a Variety of analyzers and detectors, for each element to be measured, a separate analyzer and A separate detector is provided. This allows the signals recorded simultaneously at different wavelengths will. The wavelength dispersive spectrometers therefore very powerful and have a high resolution on.

However, a disadvantage of the required high expenses due of many detectors and associated Meßelektroniken for each wavelength region and the increased susceptibility due to the large number of highly sensitive components. In particular, the required large amount of detectors and each associated independent measurement electronics make such Spectrometer also quite expensive.

WO 97/05474, in turn, is a wavelength dispersive X-ray fluorescence spectrometer, in which for a plurality of Analyzers that operate in different wavelength ranges, only a single detector is provided. However, this spectrometer does not allow simultaneous Measurements of the light from all the analyzers, but the detector can only the light from a single analyzer record, tape. Through an appropriate mechanism be at this unit the different monochromators, each from a focusing analyzer crystal with inputs and Exit slit made successively between the test sample brought and the detector, gradually the individual Later parts of the spectrum recorded.

A disadvantage of this arrangement on the one hand the sequential POSSIBILITY OF only a single spectral line, which results in that the spectrometer compared with other known wavelength dispersive devices such as cited the above "MRS 4000" extremely slow working. Although for a variety of different wavelength ranges the same detector is used, whose usually naturally existing energy dispersion but not exploited. Furthermore, in the An apparatus according to WO 97/054 74 of high mechanical effort disadvantageous because of the moving assembly, whereby the complicated mechanism in practice often malfunction will lead.

Object of the present invention contrast, it is a Spectrometer for the simultaneous measurement of several spectral lines present embodying the characteristics described in the introduction, on the one hand the high resolution known wavelength dispersive devices with relatively short measuring times due to various of simultaneous measurements wavelength ranges is to be achieved, on the other hand the expenditure on apparatus, in particular the number of detectors and associated Meßelektroniken is significantly reduced, without spending a considerably higher expenditure on equipment in mechanical range drive must.

This object is in a surprisingly simple and effective way solved by the same at least two different wavelength selectors can perform detector light from the sample to be measured, and that the detector is energy-dispersive and a sufficiently large Resolution has to the detected light of various wavelengths from the at least two different Wavelength selectors in terms of energy to separate.

The spectrometer according to the invention therefore is first as in a conventional wavelength dispersive spectrometer over single wavelength selectors only the characteristic Radiation of the elements to be analyzed from the selected from the sample-derived total radiation. subsequently but then several characteristic lines energy dispersive simultaneously by a single detector processed, thereby reducing the number of detectors in comparison to a conventionally operating simultaneously wavelength dispersive Spectrometer at least by the factor 2, wherein but reduce embodiments, a higher factor leaves. Unlike a purely energy-dispersive Spectrometer arrives at the spectrometer according to the invention hardly background radiation in the detector and the detector is not a major constituent of the sample overloaded derived radiation which the counting statistics for the remaining elements of interest substantially improved. In principle, the positive properties of the invention a wavelength dispersive simultaneous spectrometer separate by merging several wellenlängendispersiv Lines on a single detector with the advantages a conventional energy-dispersive arrangement combined without the disadvantages having to be accepted.

In a particularly preferred embodiment, the invention is Spectrometer an X-ray fluorescence spectrometer, wherein the signal detected by the test sample light ray fluorescence light is. Especially for this purpose was Spectrometer according to the invention designed to give but the above-described basic idea of ​​a combination of the positive attributes of an energy spectrometer and a wavelength dispersive arrangement quite can be transferred to other wavelength ranges.

If relatively expensive detectors are to be used, which do not have too much energy resolution is it is advantageous to provide a plurality of detectors, each Only a few, in the simplest case of two different supplied wavelength selectors light from the measurement sample get. Even at a relatively low energy resolution the detector it will always be possible, from the interest two suitable characteristic lines select (or narrow wavelength ranges), the far enough apart to also by a detector low Energy resolution to be safely disconnected.

In extreme cases, but can also all interesting characteristic Lines of only a single detector with correspondingly High resolution be processed. This should then an energy resolution .DELTA.E <200eV, preferably .DELTA.E <30eV possess at each E = 5,9keV.

Advantageously, the components of the invention Spectrometer selected so that the resolving power of Wavelength selectors is higher than the resolving power of the respectively associated detector. This allows relatively narrowly limited wavelength ranges within a broader Energy resolution range of not too expensive detector be accommodated so that they simultaneously by the detector be perceived separately.

In a particularly cost-saving embodiment of the invention Spectrometer, the various wavelength selectors essentially in a plane in a star shape arranged around a axis between the measuring sample and the detector. This spatial arrangement utilizes the available standing Place optimally, so that this embodiment of the spectrometer can be built particularly compact.

In a preferred embodiment of the invention Spectrometer comprises a wavelength selector a focusing Optics with an entrance slit, an analyzer element and an exit gap.

In developments of this embodiment, the analyzer elements can his usual crystals.

Alternatively, in other developments, the analyzer elements but also be multilayer structures.

Preferably, the analyzer elements are concave having curvature and thus focusing properties in With regard to an image of the entrance slit on the have exit slit.

In particularly simply constructed arrangements have several Wavelength selectors that associated with the same detector are a common exit slit on. The entrance slit is, however, generally for each wavelength be different.

Particularly preferred is a variant in which at least having a wavelength an absorber element. Thereby the intensity of particularly strong lines at maximum Sample excitation reduced by the X-ray tube be, so that the counting statistics weaker for much Lines which are measured simultaneously on the same detector, remains sufficiently good.

Therefore, in a further development of this embodiment, the absorber elements may be designed so that the intensities assigned to the transmitted light of all the same detector Wavelength selectors by a maximum of one order of magnitude differ. In this way, the dynamic Range of the detector is not overstressed and weaker Lines to heavier lines relatively highlighted what to a considerable improvement of the counting statistics of weaker lines contributing.

For inexpensive embodiments of the invention Spectrometer that not too expensive apparatus require, are wavelength selectors 4-10 provided. are also conceivable embodiments have significantly longer wavelength selectors, for example, up to 28, as well as the above-cited device "MRS 4000" from the prior art, however, the same number of detectors needed while spectrometer according to the invention with significantly fewer detectors and associated Meßelektroniken manages.

Reasonably be at normal embodiments of Spectrometer according to the invention a detector in each case between be associated with 2 and 8 wavelength selectors. Around particularly simple and inexpensive detectors To use, such as proportional counter or scintillation counter, must be the number of allocated Wellenlängeselektoren be relatively low. In the simplest Case of only two wavelength selectors per Detector, the two energies at a low Energy resolution of the detector can be easily separated, when the two wavelength selectors only Light on one side and the other energy band of the detector let through.

Particularly preferred is an embodiment of the invention Spectrometer in which a detector semiconductor detectors be used. Since this is a relatively high energy resolution have also significantly longer wavelength selectors can be allocated per detector.

Further advantages of the invention will be apparent from the description and the drawing. Also, the above mentioned features and those further described below in the present invention either individually or collectively in arbitrary find combinations. The illustrated and Described embodiments are as exhaustive understand enumeration but rather have exemplary Character for describing the invention.

The invention is illustrated in the drawing and is based explained embodiments. Show it:<dl tsize="7"><dt>Fig. 1</dt><dd>an embodiment of the spectrometer according to the invention as X-ray fluorescence spectrometer with two Wavelength selectors that the same detector assigned; </dd><dt>FIG. 2</dt><dd>an embodiment with eight wavelength selectors in exploded view;</dd><dt>Fig. 3</dt><dd>schematic diagrams of energy or wavelength resolution of Detector and wavelength selectors, in which<sl><li>a) a detector two wavelength selectors</li><li>b) a detector eight wavelength selectors assigned.</li></sl></dd></dl>

In Fig. 1 is schematic horizontal section according to the invention a X-ray fluorescence spectrometer 1 for simultaneous Measuring a plurality of spectral lines of a measuring sample 2 shown. For this purpose, X-rays from an X-ray tube 3 irradiated on the measurement sample 2, the liquid, in solid or can present physical state. outgoing from the measurement sample 2 is X-ray fluorescence light in this embodiment, the invention in a double monochromator 4 on two different Pathways two different wavelength selectors supplied to each light of a specific narrow wavelength band extending from a selector for others in usually different, perform the same detector 9, the shown a schematic bottom, the right box Energy spectrum of the X-ray fluorescence light from the two Paths A and B receives.

The wavelength selectors include the double monochromator 4 each focusing optics with an entrance slit 5a, 5b, an analyzer element 6a, 6b and a common Exit slit 7. In addition, the two wavelength selectors the double monochromator 4 absorber elements 8a, 8b, which are so designed that the intensities of the the transmitted light of the two wavelength selectors A maximum differ by an order of magnitude to the dynamics the detector 9 not to irritate.

The analyzer elements 6a, 6b can be single crystals or Multilayer structures may be constructed. In the embodiment shown have they each have a concave curvature, to the collected from the entrance slits 5a, 5b ray fluorescence light reflect on the common outlet gap. 7

can instead of two wavelength selectors as shown in Fig. 1 in other embodiments, also significantly more its wavelength selectors same detector assigned. Fig. 2 shows an embodiment of an X-ray fluorescence spectrometer 21, in which X-rays from an X-ray tube 23 of a test sample 22 as X-ray fluorescence emitted and by eight different paths depending Wavelength eight different wavelength selectors, which in the drawing only by its analyzer elements 26a are represented to 26h, the same detector 29 is supplied. Here, the various wavelength selectors essentially in a plane in a star shape about an axis between the test sample 22 and the detector 29 arranged. a captured An example from the detector 29 Spectrum of the light from the paths a to h is in the Diagram in the box shown on the top right in FIG. 2.

One can recognize the characteristic lines of eight elements from the measurement sample 22, the signals on the eight different Wavelength selectors the detector 29 fed simultaneously were.

In extreme cases, all the characteristic lines can range from a processed single detector with a correspondingly high resolution are, as in the example of Fig. 2 of Case. but it is also possible to provide only two characteristic Lines, as shown in Fig. 1, with a detector to separate, then a correspondingly lower resolution may have.

In Fig. 1, only one double monochromator 4 is provided with a associated detector 9 shown. In an inventive But X-ray fluorescence spectrometer 1 can also several of these double monochromators 4 with its associated Detector 9 rotationally symmetrical about an axis A by the be arranged measuring sample. 2 It can then be analyzed to Elements are put together so that even with very simple detectors such as proportional counters or Szintilationszählern the two energies the two wavelength selectors can be separated.

The detectors 9, 29 can also serve as semiconductor detectors be executed.

Essential for the invention is that the detectors 9, 29 are energy dispersive and a sufficiently large resolution own to the detected light of different Wavelengths of the different wavelength selectors energetically to separate.

In the figures 3a and 3b are examples of the energy resolution in a spectral diagram (intensity I on energy E) applied.

Fig. 3a shows the case of only two wavelength selectors, which are associated with the same detector (see Spectrometer 1 in Fig. 1), while Fig. 3b schematically the represents the case that a single detector eight assigned wavelength selectors (see also Fig. 2). In order to obtain reasonable results, is usually the resolution of the wavelength selectors (dashed be curves in Figures 3a and 3b) is higher than the Resolution of the associated detector (Solid curves in Figures 3a and 3b).

In the in Fig. 3a example shown, the detector quite a moderately good energy resolution in the region .DELTA.E ≈ 1000-2000 eV at E ≈ have 6 keV. If the wavelength selectors are selected in accordance with, the two to dividing lines even with a poor energy resolution the detector are so far apart that they total in the spectrum can still be resolved.

In the case of Fig. 3b, however, a detector with significantly better energy resolution is required, for example .DELTA.E &lt;200 eV, preferably .DELTA.E ≤ 30 eV at E = 5.9 keV. This is of course a much higher expense bought at the sides of the detector, however, where for the same Number of different wavelength bands substantially fewer detectors are required. The detector in Example of Fig. 3b serves at least four times as many wavelength selectors as the detector in the example of FIG. 3a. With progressive development of available stationary detectors can with the basic idea of ​​the invention therefore a particularly compact spectrometers are built, with the still a large number of different added lines in different wavelength ranges can be.