HK1070984B - An x-ray fluorescence spectroscopy system and an xrf spectroscopy method - Google Patents

Description

X-ray fluorescence (XRF) spectrometry systems and methods

CROSS-REFERENCE TO RELATED PATENT/APPLICATIONS

This application contains subject matter related to the subject matter of the following commonly owned patents and applications, each of which is hereby incorporated by reference in its entirety:

"Use Of Kumakhov Lens For X-Ray Li pathology", Muradin A. Kumakhov, U.S. patent certificate 5175755, granted on 29.12.1992;

"Device For Controlling Beams Of Particles, X-Ray and Gamma Quanta", Muradin A. Kumakhov, U.S. patent certificate 5192869, 3.9.1993;

"Use Of A Kumakhov Lens In analytical Instruments" Muradin A. Kumakhov, U.S. patent certificate 5497008, granted 3/5 1996;

"High Intensity, Small Diameter X-Ray Beam, Capillary optical System", David M.Gibson, U.S. patent certificate 5570408, published 10.29.1996;

"Multiple-Channel, Total-Reflection optical With controlled publishing," Gibson et al, U.S. patent certificate 5604353, granted 2/18/1997;

"Multiple Channel Optic", Qi-Fan Xiao, U.S. patent certificate 5745547, granted 4/28/1998;

"Current Optical Device and Method Of contamination", Zewu Chen, U.S. patent certificate 6285506, granted on 9/4/2001;

"double Current Optical Device With Graded Atomic plants", Zewu Chen, U.S. patent certificate 6317483, published 11/13/2001;

"Total-Reflection X-Ray Fluorescence Apparatus and method using a double-collected optical", Zewu Chen, U.S. application No. 09/667966, filed on 9/22/2000; and

"X-Ray Tube and Method and Apparatus for Analyzing fluid streams Using X-Rays", Radley et al, U.S. application No. 60/336584, 12/4/2001.

Technical Field

The field of the invention relates to X-ray fluorescence (XRF) spectroscopy systems, and in particular to X-ray spectroscopy systems that include focusing X-ray optics for forming a focused excitation beam on a sample and a monochromator for collecting secondary X-rays from the sample.

Background

X-ray fluorescence (XRF) spectrometry is widely recognized as a very accurate method of determining the atomic composition of a material by irradiating a sample with X-rays and observing the resulting secondary X-rays emitted by the sample.

Typically, an XRF system includes a source of exciting radiation (an X-ray tube or radioisotope), means for detecting secondary X-rays emitted from the sample and determining their energy or wavelength, and a display of spectral output. The intensity of the secondary X-rays of a certain energy or wavelength is related to the concentration of the element in the sample. Computer software is often used to analyze the data and determine the concentration.

This process begins by irradiating the sample with an X-ray source. When X-ray photons strike a specimen, they collide with electrons from the inner shells of atoms that make up the specimen, creating vacancies that destabilize the atoms. When an electron leaving the outer shell transfers to the inner shell, the atom stabilizes and in the process emits a typical X-ray photon, whose energy is the difference between the two binding energies of the corresponding shells. There are two conventional methods of determining the X-ray spectrum emitted from a sample. The first method is Energy Dispersive Spectroscopy (EDS), and the second method is Wavelength Dispersive Spectroscopy (WDS). In energy dispersive spectroscopy systems, an energy dispersive detector, such as a solid state detector or a proportional counter, is used to determine the energy spectrum of photons emitted from a sample. In wavelength spectrometry systems, a crystal or multilayer structure is used to select a particular X-ray wavelength from among the X-ray photons emitted by a sample.

X-ray fluorescence using EDS is the most widely used method of element concentration analysis. This approach has several advantages. First, the EDS probe can detect almost all elements in the periodic table at once. Second, the system is compact because no additional optics are required on the collection side as compared to wavelength dispersive X-ray fluorescence systems. Third, a low power X-ray tube may be used because the EDS detector has a large collection solid angle and high efficiency. XRF/EDS systems, however, have some drawbacks, including poor sensitivity and poor energy resolution. Moreover, since the EDS detector can detect all X-rays from the sample, the detector is easily saturated with fluorescence signals from the primary elements and strong scattering of the primary beam.

X-ray fluorescence using WDS also has several advantages, including higher energy resolution and higher signal-to-background ratio compared to XRF/EDS systems. Thus, the XRF/WDS method is a powerful tool for trace element analysis and applications requiring high energy resolution. However, conventional XRF/WDS systems suffer from drawbacks, including the need for high power X-ray tubes due to the limitations of the WDS approach, which results in low efficiency and small collection solid angles. Another drawback of conventional WDS systems is that the crystal and multilayer structure on the collection side only select a specific X-ray wavelength, requiring a scanning mechanism or multi-crystal system for multi-element detection. This has the advantage that saturation of the detector can be avoided, but leads to complicated adjustments. Thus, XRF/WDS systems are typically large, complex, and more expensive than XRF/EDS systems.

USP5982847 to Nelson discloses an Energy Dispersive System (EDS) that uses only polychromatic optics in the detection and collection paths. No mention is made of diffractive optics in the excitation or collection path.

WO 02/25258, which belongs to the company X-ray optical systems, also discloses an EDS system in strict terms. Even with monochromatic excitation, the detection path is not limited to a particular wavelength using detection optics, and the document does not disclose or teach detection optics. Thus, the detection system employs a wider wavelength bandwidth and processes that bandwidth using conventional EDS techniques.

EP0339713 to n.v. philips discloses a WDS system, however, as mentioned above, this document discloses the conventional technique of illuminating a large sample area, the aperture/slit 6 defining the angle of incidence on the optics 22, thus severely limiting the collection solid angle. It does not disclose, teach or suggest the focusing optics involved in the present invention, providing small sample focal spot sizes, and additional advantages. The small sample focal spot size of the present invention is at position 6 but does not limit the collection solid angle of the detection optics.

The authors are Chen et al, "Microprobe X-Ray Fluorescence with the use of Point-Focusing diffacters,", appl. Phys Lett.71(13)1884-1886, 9 months, 1997, analogously to the above-mentioned WO 02/25258. Even with monochromatic excitation, the detection path is not limited to a particular wavelength using detection optics, and the document does not disclose or teach detection optics.

USP5406609 to Arai et al is also similar to WO 02/25258 described above. Monochromatic excitation with standard EDS detection scheme.

Although most XRF instruments are commonly used to analyze multiple elements, they also have many important applications in industrial process control, which require single element or limited elemental detection. Thus, the present invention is directed to providing a compact XRF/WDS system that provides ultra-high sensitivity or high-speed analysis for a limited number of elements.

Disclosure of Invention

The present invention overcomes the disadvantages of the prior art and provides additional advantages. One aspect of the invention includes an X-ray fluorescence (XRF) spectroscopy system. The XRF system includes at least one X-ray radiation source, and at least one excitation optic disposed between the at least one X-ray radiation source and the sample. At least one excitation optic collects X-ray radiation from the at least one radiation source and focuses the X-ray radiation to a focal point on the sample to cause fluorescence from at least one analyte in the sample. The system also includes at least one X-ray detector, and at least one collection optic. The at least one collection optic includes at least one doubly curved diffractive optic disposed between the specimen and the at least one X-ray detector to collect X-ray fluorescence from a focal point on the specimen and direct the fluorescent X-rays to the at least one X-ray detector.

Many improvements in the above-described XRF spectroscopy systems are also described and claimed. For example, the at least one source of X-ray radiation comprises at least one electron-bombardment X-ray source. The at least one excitation optic includes at least one focusing polychromatic optic, such as one or more polycapillary (polycapillary) optics, and/or includes at least one focusing monochromatic optic. The one or more focusing monochromating optics comprise at least one doubly-curved crystal and/or at least one doubly-curved multilayer optic. The focal spot has a focal spot size of less than 500 microns and the sample may be a solid or a fluid. Also, the sample may be a petroleum-based product such as gasoline, diesel, crude oil, or lubricating oil. The at least one analyte excited in the sample comprises sulfur and/or iron. In addition, the X-ray radiation focused on the specimen may be incident on the specimen at an angle smaller than the angle of total external reflection, which is desirable for total reflection X-ray fluorescence (TXRF), or the X-ray radiation focused on the specimen may be incident on the specimen at an angle larger than the angle of total external reflection, which is desirable for normal X-ray fluorescence.

Other improvements may include at least one collection optic directing X-rays of the at least one analyte toward the detector for determining the concentration of the at least one analyte in the sample, or determining the thickness of the sample. Furthermore, the at least one doubly curved diffractive optic of the at least one collection optic comprises at least one doubly curved crystal. At least one doubly-curved crystal has a Johann profile, a Johannson profile, a partial approximation of a Johannson profile, or includes logarithmic spiral crystal optics. Also, the at least one doubly curved diffractive optic includes at least one doubly curved multilayer optic, which may be a doubly curved stepped optic, or in some embodiments a doubly curved logarithmic spiral optic. Furthermore, the at least one collection optic may be fixed relative to the sample and the at least one X-ray detector. The at least one X-ray detector may be one or more gas proportional counters, one or more scintillation counters, and/or one or more solid state detectors. The one or more solid state detectors include at least one PIN diode solid state detector.

In another aspect, an X-ray fluorescence spectrometry method is disclosed. The method comprises the following steps: providing at least one source of X-ray radiation; providing at least one excitation optic disposed between the at least one source of X-ray radiation and a sample being analyzed to collect X-ray radiation from the at least one source and focus the X-ray radiation to a focal point on the sample to cause at least one analyte in the sample to fluoresce; providing at least one X-ray detector; and arranging at least one collection optic between the specimen and the at least one X-ray detector, the collection optic comprising at least one doubly curved diffractive optic to collect X-ray fluorescence from said focal point on the specimen and focus the fluorescent X-rays toward the at least one X-ray detector.

Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail below and form a part of the invention.

Drawings

The subject matter which comprises the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features and advantages of the invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings. In the drawings:

FIG. 1 depicts one embodiment of an XRF/WDS system 100, in accordance with an aspect of the present invention;

FIG. 2 shows a doubly curved crystal optic providing point-to-point focusing for use in a system according to the invention;

FIG. 3A shows one embodiment of a profile of a hyperbolic logarithmic spiral crystal or multilayer optic for use in a system according to the invention;

FIG. 3B shows a cross-sectional view of the optical device taken along line B-B in FIG. 3A;

FIG. 4 illustrates another embodiment of an XRF/WDS system 200 in accordance with an aspect of the present invention; and

figure 5 shows a polycapillary optic providing point-to-point focusing for use in a system according to one aspect of the invention.

Detailed Description

In general, one embodiment of a compact XRF/WDS system in accordance with an aspect of the present invention includes an X-ray source, an excitation X-ray optic that focuses X-rays from the X-ray source onto a sample, at least one collection monochromator, and an X-ray counter. The excitation X-ray optic may be a focusing polycapillary optic providing polychromatic excitation, or a point focusing hyperbolic crystal optic providing monochromatic excitation. A collection monochromator (which may be a doubly curved crystal optic, a doubly curved multilayer optic, or other doubly curved diffractive optic) selects the desired elemental characteristic wavelength. The intensity of the reflected X-rays is measured by a detector and is related to the concentration of the element in the sample.

One aspect of an XRF/WDS system in accordance with the present invention is that the excitation optics may effectively capture large cone angle X-rays from a point X-ray source. The optics are focusing optics which can produce a very strong excitation beam on the sample even with a compact, low power (e.g. < 1KW, more advantageously < 100W) X-ray source. The use of a low power X-ray tube makes the system more compact and simpler than conventional XRF/WDS systems using high power X-ray tubes.

Another aspect of the invention is that if a doubly curved crystal optic is used as the excitation optic, a monochromatic excitation beam can be produced. In one exemplary embodiment of an XRF/WDS system, a polychromatic beam is used to excite a sample. Monochromatic excitation produces a higher signal background ratio than polychromatic excitation because the scattered bremsstrahlung radiation from the X-ray source is eliminated on the sample. This significantly improves the detection range of the system. Monochromatic excitation also greatly simplifies quantitative analysis of XRF.

It is yet another aspect of the present invention that the excitation beam is focused on the specimen due to the focusing capabilities of the excitation optics. The focal spot size of the beam on the specimen may be in the range of 50 μ to 500 μ, which is about two orders of magnitude smaller than the beam size of conventional systems (typically-10 mm-30 mm). In addition to providing efficient collection, this smaller beam size allows for spatial resolution in analysis.

Due to the smaller specimen excitation area, the doubly curved diffractive optic can be effectively used as a collection optic (in another aspect of the invention). Doubly-curved monochromating optics can provide a large solid collection angle from one spot. (in conventional XRF/WDS systems with large excitation beam sizes, a flat or single curved monochromator is chosen, which limits the collection solid angle). For a given shape and intensity of the excitation beam, the hyperbolic monochromator significantly increases the signal level for detecting the elements.

It is a further aspect of the present invention that the collection optics may be fixed relative to the sample and probe without involving moving parts. This has both advantages and disadvantages. The advantage is that it speeds up the analysis and improves the system reliability, while the disadvantage is that multiple collection optics have to be used, e.g. for multi-element analysis.

To reiterate, in accordance with the principles of the present invention, an XRF/WDS system is described having X-ray focusing optics that provide polychromatic or monochromatic excitation of a sample. Secondary X-rays resulting from X-ray fluorescence are collected by a monochromator comprising a doubly curved diffractor to advance towards a detector, such as a proportional counter, room temperature PIN detector, or NaI detector. One example of an XRF/WDS system 100 utilizes, for example, X-ray optics to provide monochromatic excitation and collect X-rays from a sample, as described in more detail below with reference to FIG. 1.

XRF/WDS system 100 includes, for example, a low power X-ray source 110, monochromating focusing optics 120, a sample 130, a collection monochromator 140, and a detector 150.

The low power X-ray source 110 (e.g. < 1KW, more advantageously < 100W) is a source of X-ray radiation, such as an X-ray tube, a sealed source of radioactive material, or a high energy electron source that impinges on a metallic target and generates X-ray radiation. One example of a low power X-ray source 110 is a 50W X ray tube having a target material comprising chromium, copper, tungsten, or molybdenum, and an electron beam size on the target material in a range between about 50 μm and 300 μm.

The specimen 130 is a material that receives a metrology measurement. An example of a test sample 130 may be a process flow such as diesel where it is desired to measure the concentration of sulfur, or lubricating oil where it is desired to measure the concentration of wear metals (iron). If the specimen 130 is a fluid stream, a window material (not shown) may be included to enable transmission of X-ray excitation radiation into the specimen 130 and emission of X-ray fluorescence from the specimen 130.

Monochromatic focusing optics 120, located between X-ray source 110 and specimen 130 of XRF system 100, are used to reflect or conduct radiation in a small energy range, e.g., in an energy range between tens or hundreds of electron volts, toward specimen 130, unlike polychromatic optics, which can conduct radiation in an energy bandwidth of thousands of electron volts. The optics 120 also focus the X-rays onto a small focal spot on the specimen 130. The focal spot may have a size in a range between 50 μm and 500 μm.

One example of focusing optics 120 is a Johann-type doubly-curved crystal. An example of the profile of a Johann-type doubly curved crystal is illustrated in fig. 2. In this profile, the diffraction plane of the crystal 160 is parallel to the crystal surface. The curved crystal surface has a Johann' S profile in the plane of focal circle 170 and is axisymmetric along line SI, where point S is the position of X-ray source 110 (FIG. 1) and point I is the focal spot. The crystal surface has a radius of curvature of 2R in the plane of the focal circle and 2Rsin in the mid-plane perpendicular to the sector SI²θ_BWherein R is the radius of the focal circle, theta_BIs the bragg angle, X-rays that diverge from point S and reach the crystal surface at an angle of incidence within the rocking curve width of the crystal are effectively reflected to point I. This type of doubly curved crystal not only provides point focusing, but also monochromatization of the beam 180, since only X-ray photons having the appropriate wavelength can be reflected.

As shown in FIG. 1, X-ray optic 140 is another monochromating optical element of XRF system 100 and is positioned between sample 130 and detector 150. The optical device collects X-rays of a specific wavelength and directs the X-rays to an X-ray detector. In conventional XRF/WDS systems, flat and single-bend crystal optics may be used as an option for the optics. In the present invention, a collection monochromator is a doubly curved diffractive body (e.g., a crystal or multilayer optic) that can provide a larger collection solid angle from one point than a flat/single curved optic.

One particular example of collection monochromating optic 140 is a hyperbolic log-spiral crystal optic. An example of this profile is illustrated in fig. 3A and 3B. In this profile, the diffraction plane of the crystal optic is parallel to the crystal surface. The crystal surface in the dispersion plane has the shape of a logarithmic spiral and is rotationally symmetrical about axis ID, where point I is the origin of the logarithmic spiral and the focal point of the excitation beam on the specimen 130 (fig. 1) and point D is the position of the probe 150 (fig. 1). Due to the nature of the helical curve, the fluorescent X-rays emitted from point I on the sample surface have a constant angle of incidence on the logarithmic spiral surface. For the diffraction plane of the crystal, the constant angle is chosen to be the bragg angle of the characteristic X-rays of the element of interest in the sample 130. X-rays reflected from a hyperbolic logarithmic spiral profile do not form a point, but are caustic in the plane of dispersion. The X-ray will be focused on the axis ID in the direction of ID, as shown in fig. 3B.

Alternatively, a multilayer optic may be used as monochromating optic 120 and monochromating optic 140 in the system of FIG. 1. The detector 150 may be a simple counting detector, i.e., a gas proportional counter, a scintillation detector, or a room temperature PIN diode solid state detector.

Advantageously, the XRF/WDS system 100 is well suited for highly sensitive trace element analysis. Point-to-point focusing hyperbolic crystal optics provide a large collection solid angle and form a strongly focused monochromatic beam on a sample even with a low power X-ray tube. Due to the monochromatic excitation, the signal background ratio is significantly increased and the detection sensitivity is increased. Focusing the excitation beam spot on the sample enables efficient use of hyperbolic collection optics to improve the solid angle of collection of fluorescent X-rays. This further improves the sensitivity of the system.

As one particular embodiment of the XRF/WDS system 100 of FIG. 1, the system includes an X-ray source 110, the X-ray source 110 including a 50W X ray tube having a source material of chromium, copper, tungsten, or molybdenum with a spot size on the source material in a range between about 100 μm and 300 μm. Optic 120 may be a doubly-curved point-focused crystal made of silicon, germanium, or other crystalline material and positioned 100mm to 200mm along the optical axis from X-ray source 110, defined as the center of travel of light rays from the X-ray source striking the center of doubly-curved crystal 120 to doubly-curved crystal 120. The sample 130 may be an oil, for example, with trace elements that may include sulfur, vanadium, and nickel. Specimen 130 may be positioned from monochromating optic 120 at a distance of 100mm to 200mm measured along the optical axis. Second monochromating optic 140 may be a hyperbolic logarithmic spiral crystal made of silicon, germanium, and other crystalline materials and positioned at a distance of 100mm to 200mm from sample 130 measured along the optical axis. The detector 150 may be a gas proportional counter, a scintillation counter, a room temperature PIN detector, or a NaI detector, and is positioned from 100mm to 200mm from the sample 130 measured along the optical axis.

Two or more elements may be measured by adding one or more collection monochromators and detectors to system 100, each paired with a detector for corresponding single element detection.

Fig. 4 illustrates an alternative embodiment of an XRF system 200 in accordance with an aspect of the subject invention. System 200 includes a source 210, polychromatic focusing optics 220, a sample 230, hyperbolic monochromating optics 240, and a detector 250.

The polychromatic optic 220 is an optical element that conducts a wide range of photon energies and focuses the photons onto a small spot on the sample 230 at the same time. One example of a polychromatic optic that is well suited to function as optic 220 is a polycapillary optic 300 (see FIG. 5), such as is commercially available from X-ray optical systems of Albany, New York. The polycapillary optics described in detail in the above-mentioned patent is a bundle of thin hollow tubes which conduct photons by total reflection.

Due to the polychromatic excitation, the signal to background ratio is worse compared to system 100 (fig. 1). However, system 200 (fig. 4) may provide several advantages. For example, for system 200, a smaller focal spot may be obtained due to the better focusing capabilities of the polycapillary optics. For local analysis this may give better spatial resolution. For example, a 20 μm to 50 μm focal spot may be obtained with a 50W X tube and multi-capillary optics. Another advantage is that polychromatic excitation provides X-ray photons with a wide range of energies, which can cover almost all elements of the periodic table.

In one particular embodiment, the XRF/WDS system 200 may include an X-ray source 210, which may be a 50W X ray tube, with a source material of chromium, copper, tungsten, or molybdenum, and a focal spot size on the source material of approximately 100 μm to 300 μm. The polychromatic optics 220 may be a polycapillary optics at a distance of 30mm to 50mm from the X-ray source 210. The sample 230 may, for example, be an oil having elements including sulfur, vanadium, and nickel. The specimen 230 may be positioned at a distance of 100mm to 200mm from the polycapillary optics 220. Hyperbolic monochromator 240 may be a hyperbolic logarithmic spiral crystal made of silicon, germanium, or other crystalline material and positioned at a distance of 100mm to 200mm from sample 230 measured along the optical axis. Detector 250 may be a gas proportional counter, a scintillation counter, a room temperature PIN detector, or a NaI detector positioned at a distance of 100mm to 200mm from monochromating optic 240 measured along the optical axis. Multiple collection monochromators with corresponding detectors can also be used for multi-element detection.

While preferred embodiments have been depicted and described herein, it will be apparent to those skilled in the relevant art that various modifications, additions, substitutions and the like can be made without departing from the spirit of the invention as defined in the following claims.

Claims (57)

1. An X-ray fluorescence (XRF) spectroscopy system, the system comprising:

at least one X-ray radiation source (110/210), at least one X-ray detector (150/250), and at least one monochromating collection optic (140/240) comprising at least one doubly curved diffractive optic disposed between the test sample (130/230) and the at least one X-ray detector, the at least one doubly curved diffractive optic for collecting X-ray fluorescence from a focal point on the test sample and directing fluorescent X-rays of a characteristic energy of a predetermined analyte to the at least one X-ray detector;

the method is characterized in that:

at least one excitation optic (120/220) disposed between the at least one source of X-ray radiation and the sample for collecting X-ray radiation from the at least one source of radiation and focusing the X-ray radiation to a focal point on the sample to cause fluorescence of the analyte in the sample.

2. The XRF spectroscopy system of claim 1, wherein the at least one source of X-ray radiation (110) comprises at least one electron bombardment X-ray source.

3. The XRF spectroscopy system of claim 1, wherein the at least one excitation optic comprises at least one focusing polychromatic optic (220).

4. The XRF spectroscopy system of claim 3, wherein the at least one focusing polychromatic optic comprises at least one polycapillary optic.

5. The XRF spectroscopy system of claim 1, wherein the at least one excitation optic comprises at least one focusing monochromating optic (120).

6. The XRF spectroscopy system of claim 5, wherein the at least one focusing monochromating optic comprises at least one doubly curved crystal.

7. The XRF spectroscopy system of claim 5, wherein the at least one focusing monochromating optic comprises at least one doubly curved multilayer optic.

8. The XRF spectroscopy system of claim 1, wherein the focal spot has a focal spot size of less than 500 microns.

9. The XRF spectroscopy system of claim 1, wherein the X-ray radiation focused on the sample is incident on the sample at an angle less than the angle of total external reflection.

10. The XRF spectroscopy system of claim 1, wherein the X-ray radiation focused on the sample is incident on the sample at an angle greater than the angle of total external reflection.

11. The XRF spectroscopy system of claim 1, wherein the sample comprises a solid.

12. The XRF spectroscopy system of claim 1, wherein the sample comprises a fluid.

13. The XRF spectroscopy system of claim 12, wherein the fluid comprises a petroleum-based product.

14. The XRF spectroscopy system of claim 13, wherein the petroleum-based product comprises gasoline or diesel.

15. The XRF spectroscopy system of claim 13, wherein the petroleum-based product comprises crude oil.

16. The XRF spectroscopy system of claim 11, wherein the petroleum-based product comprises a lubricant.

17. The XRF spectroscopy system of claim 1, wherein the at least one analyte comprises sulfur.

18. The XRF spectroscopy system of claim 1, wherein the at least one analyte comprises iron.

19. The XRF spectroscopy system of claim 1, wherein the at least one collection optic (140/240) directs X-rays of the analyte toward the at least one X-ray detector to determine a concentration of the analyte in the sample or to determine a thickness of the sample.

20. The XRF spectroscopy system of claim 1, wherein the at least one doubly curved diffractive optic comprises at least one doubly curved crystal.

21. The XRF spectroscopy system of claim 20, wherein the at least one doubly curved crystal comprises at least one doubly curved crystal having Johann's profile.

22. The XRF spectroscopy system of claim 20, wherein the at least one doubly curved crystal comprises at least one doubly curved crystal having Johannson profile or a portion of Johannson profile.

23. The XRF spectroscopy system of claim 20, wherein the at least one doubly curved crystal comprises at least one doubly curved logarithmic spiral crystal optic.

24. The XRF spectroscopy system of claim 1, wherein the at least one doubly curved diffractive optic comprises at least one doubly curved multilayer optic.

25. The XRF spectroscopy system of claim 24, wherein the at least one doubly curved multilayer optic comprises at least one doubly curved logarithmic spiral optic.

26. The XRF spectroscopy system of claim 1, wherein the at least one doubly curved diffractive optic comprises at least one doubly curved stepped diffractive optic.

27. The XRF spectroscopy system of claim 1, wherein the at least one collection optic (140/240) is fixed relative to the sample and fixed relative to the at least one X-ray detector.

28. The XRF spectroscopy system of claim 1, wherein the at least one X-ray detector comprises at least one gas proportional counter.

29. The XRF spectroscopy system of claim 1, wherein the at least one X-ray detector comprises at least one scintillation counter.

30. The XRF spectroscopy system of claim 1, wherein the at least one X-ray detector comprises at least one solid state detector.

31. The XRF spectroscopy system of claim 30, wherein the at least one solid state detector comprises at least one PIN diode solid state detector.

32. The XRF spectroscopy system of claim 1, wherein the system is a wavelength dispersive spectroscopy system.

33. The XRF spectroscopy system of claim 1, wherein the at least one doubly curved diffractive optic is positioned such that an input focus of the at least one doubly curved diffractive optic at a focus of the sample corresponds to an output focus of the at least one excitation optic.

34. A method of X-ray fluorescence (XRF) spectroscopy, the method comprising:

providing at least one X-ray radiation source (110/210), providing at least one X-ray detector (150/250), and disposing at least one monochromating collection optic (140/240) between the test sample (130/230) and the at least one X-ray detector, the monochromating collection optic comprising at least one doubly curved diffractive optic to collect X-ray fluorescence from a focal point on the test sample and direct fluorescent X-rays of a characteristic energy of a predetermined analyte to the at least one X-ray detector;

the improvement comprises:

at least one excitation optic (120/220) is provided and is disposed between the at least one source of X-ray radiation and a sample being analyzed to collect X-ray radiation from the at least one source and focus the X-ray radiation to a focal point on the sample to cause fluorescence of the analyte in the sample.

35. The XRF spectroscopy method of claim 34, wherein the at least one X-ray radiation source (110) comprises at least one electron bombardment X-ray source.

36. The XRF spectroscopy method of claim 34, wherein the at least one excitation optic comprises at least one focusing polychromatic optic (220).

37. The XRF spectroscopy method of claim 36, wherein the at least one focusing polychromatic optic comprises at least one polycapillary optic.

38. The XRF spectroscopy method of claim 34, wherein the at least one excitation optic comprises at least one focusing monochromating optic (120).

39. The XRF spectroscopy method of claim 38, wherein the at least one focusing monochromating optic comprises at least one doubly curved crystal.

40. The XRF spectroscopy method of claim 38, wherein the at least one focusing monochromating optic comprises at least one doubly curved multilayer optic.

41. The XRF spectroscopy method of claim 34, wherein the focal spot has a focal spot size of less than 500 microns.

42. The XRF spectroscopy method of claim 34, wherein the sample comprises a solid.

43. The XRF spectroscopy method of claim 34, wherein the sample comprises a fluid.

44. The XRF spectroscopy method of claim 43, wherein the fluid comprises a petroleum-based product.

45. The XRF spectroscopy method of claim 44, wherein the petroleum-based product comprises gasoline or diesel.

46. The XRF spectroscopy method of claim 45, wherein the at least one analyte comprises sulfur.

47. The XRF spectroscopy method of claim 34, wherein the at least one doubly curved diffractive optic comprises at least one doubly curved crystal.

48. The XRF spectroscopy method of claim 47, wherein the at least one doubly curved crystal comprises at least one doubly curved crystal having Johann's profile.

49. The XRF spectroscopy method of claim 47, wherein the at least one doubly curved crystal comprises at least one doubly curved crystal having Johannson profile or partial Johannson profile.

50. The XRF spectroscopy method of claim 47, wherein the at least one doubly curved crystal comprises at least one doubly curved logarithmic spiral crystal optic.

51. The XRF spectroscopy method of claim 34, wherein the at least one doubly curved diffractive optic comprises at least one doubly curved multilayer optic.

52. The XRF spectroscopy method of claim 51, wherein the at least one doubly curved multilayer optic comprises at least one doubly curved logarithmic spiral optic.

53. The XRF spectroscopy method of claim 34, wherein the at least one doubly curved diffractive optic comprises at least one doubly curved stepped diffractive optic.

54. The XRF spectroscopy method of claim 34, wherein the at least one X-ray detector comprises at least one gas proportional counter.

55. The XRF spectroscopy method of claim 34, wherein the at least one X-ray detector comprises at least one scintillation counter.

56. The XRF spectroscopy method of claim 34, wherein the method is carried out in a wavelength dispersive spectroscopy system.

57. The XRF spectroscopy method of claim 34, wherein the at least one doubly curved diffractive optic is positioned such that an input focus of the at least one doubly curved diffractive optic at a focus of the sample corresponds to an output focus of the at least one excitation optic.