X-ray tube and method and apparatus for analyzing fluid streams using x-rays Number:7,072,439 from the United States Patent and Trademark Office (PTO) owispatent

Title: X-ray tube and method and apparatus for analyzing fluid streams using x-rays

Abstract: A technique for analyzing fluids by means of x-ray fluorescence applicable to any fluid, including liquids and gases, which emit x-ray fluorescence when exposed to x-rays. The apparatus includes an x-ray source (82) including an x-ray tube (64) having improved heat dissipating properties due to a thermally-conductive, dielectric material (70, 1150). The x-ray tube also includes means for aligning (100, 2150, 2715) the tube with the source housing whereby the orientation of the x-ray beam produced by the source can be optimized, and stabilized over various operating conditions. The method and apparatus may also include an x-ray detector having a small-area, for example, a PIN-diode type semiconductor x-ray detector (120), that can provide effective x-ray detection at room temperature. One aspect of the disclosed invention is most amenable to the analysis of sulfur in petroleum-based fuels.

Patent Number: 7,072,439 Issued on 07/04/2006 to Radley,   et al.

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Inventors:	Radley; Ian (Glenmont, NY); Bievenue; Thomas J. (Delmar, NY); Burdett, Jr.; John H. (Charlton, NY); Gallagher; Brian W. (Guilderland, NY); Shakshober; Stuart M. (Hudson, NY); Chen; Zewu (Schenectady, NY); Moore; Michael D. (Alplaus, NY)
Assignee:	X-Ray Optical Systems, Inc. (East Greenbush, NY)
Appl. No.:	858173
Filed:	June 1, 2004

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Related U.S. Patent Documents

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	Application Number	Filing Date	Patent Number	Issue Date
	PCT/US02/38792	Dec., 2002
	10206531	Jul., 2002	6781060
	60398968	Jul., 2002
	60383990	May., 2002
	60398965	Jul., 2002
	60398966	Jul., 2002
	60336584	Dec., 2001

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Current U.S. Class:	378/47
Current International Class:	G01N 23/223 (20060101)
Field of Search:	378/44-50

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References Cited [Referenced By]

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U.S. Patent Documents

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	4674109		June 1987		Ono
	4810776		March 1989		Karlhuber et al.
	5550889		August 1996		Gard et al.
	5581591		December 1996		Burke et al.
	5598451		January 1997		Ohno et al.
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	6487273		November 2002		Takenaka et al.
	6498830		December 2002		Wittry

Primary Examiner: Glick; Edward J.
Assistant Examiner: Yun; Jurie
Attorney, Agent or Firm: Klembczyk, Esq.; Jeffrey R. Radigan, Esq.; Kevin P. Heslin Rothenberg Farley & Mesiti, P.C.

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Parent Case Text

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CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT Application PCT/US02/38792, filed Dec. 4, 2002, and published under PCT Article 21(2) in English as WO 03/048745 A2 on Jun. 12, 2003. PCT/US02/38792 claimed the priority of the United States applications identified below, which are assigned to the same assignee as this application. The entire disclosures of PCT/US02/38792 and the below-listed applications are hereby incorporated herein by reference in their entirety:

"X-RAY TUBE AND METHOD AND APPARATUS FOR ANALYZING FLUID STREAMS USING X-RAYS" by Radley, et al. U.S. Ser. No. 60/336,584 filed Dec. 4, 2001;

"A METHOD AND APPARATUS FOR DIRECTING X-RAYS" by Radley, U.S. Ser. No. 60/383,990 filed May 29, 2002;

"X-RAY SOURCE ASSEMBLY HAVING ENHANCED OUTPUT STABILITY" by Radley, et al., U.S. Ser. No. 60/398,965 filed Jul. 26, 2002;

"METHOD AND DEVICE FOR COOLING AND ELECTRICALLY INSULATING A HIGH-VOLTAGE, HEAT-GENERATING COMPONENT" by Radley, U.S. Ser. No. 60/398,968 filed Jul. 26, 2002;

"AN ELECTRICAL CONNECTOR, A CABLE SLEEVE, AND A METHOD FOR FABRICATING AN ELECTRICAL CONNECTION" by Radley, U.S. Ser. No. 10/206,531 filed Jul. 26, 2002; and

"DIAGNOSING SYSTEM FOR AN X-RAY SOURCE ASSEMBLY" by Radley, et al., U.S. Ser. No. 60/398,966 filed Jul. 26, 2002.

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Claims

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The invention claimed is:

1. A wavelength dispersive apparatus for analyzing a fluid using x-rays, comprising: means for exposing the fluid to focused x-rays to cause at least one component of the fluid to x-ray fluoresce, including: a first focusing optic for focusing the x-rays on the fluid, and at least one x-ray exposure chamber, having an exposure aperture less than about 10 mm in diameter; means for analyzing x-ray fluorescence to determine at least one characteristic of the fluid, including: at least one x-ray detector having an active area operating at a temperature greater than about 0 degrees centigrade and substantially uncooled; and a second focusing optic to collect x-ray fluorescence from the fluid, and focus said x-ray fluorescence on the detector; wherein at least one of the first or second focusing optics is a monochromating optic providing wavelength dispersion for the focused x-rays and/or the x-ray fluorescence from the sample.

2. The apparatus of claim 1, wherein the at least one characteristic of the fluid comprises a concentration of at least one component in the fluid.

3. The apparatus of claim 2, wherein the fluid is fuel, and the at least one characteristic is the concentration of sulfur in the fuel.

4. The apparatus of claim 1, wherein the detector comprises at least one semiconductor-type x-ray detector.

5. The apparatus of claim 4, wherein the detector comprises at least one PIN-diode-semiconductor-type x-ray detector.

6. The apparatus of claim 4, wherein the semiconductor-type x-ray detector comprises a detector active area having an area less than about 10 square millimeters.

7. The apparatus of claim 6, wherein the semiconductor-type x-ray detector comprises a detector active area having an area less than about 6 square millimeters.

8. The apparatus of claim 4, wherein the detector has no protective window.

9. The apparatus of claim 1, wherein the means for exposing the fluid to x-rays is enclosed in a chamber held under vacuum.

10. The apparatus of claim 1, wherein the x-ray exposure aperture is less than about 5 mm in diameter.

11. The apparatus of claim 1, wherein the fluid comprises a continuous, pressurized fluid stream, the apparatus further comprising: means for delivering the continuous fluid stream to the means for analyzing.

12. The apparatus of claim 1, further comprising: an x-ray source including an x-ray tube for generating the x-rays; and a thermally-conductive, dielectric material thermally coupled to the x-ray tube for removing heat generated by the x-ray tube.

13. The apparatus of claim 1, further comprising: an x-ray tube having an anode for generating x-rays; wherein the first focusing optic collects x-rays generated by the anode; and a control system for controlling x-ray output intensity of the first focusing optic, wherein the control system can maintain x-ray output intensity notwithstanding a change in at least one operating condition of the apparatus.

14. The apparatus of claim 13, wherein the control system further includes a sensor for monitoring x-ray output intensity of the first focusing optic and a controller for controlling position of at least one of the anode and the first focusing optic using monitored x-ray output intensity.

15. The apparatus of claim 1, wherein at least one of the focusing optics comprises a polycapillary focusing optic.

16. The apparatus of claim 1, wherein at least one of the focusing optics comprises a curved crystal monochromating optic.

17. The apparatus of claim 16, wherein both focusing optics comprise doubly curved crystal monochromating optics.

18. A wavelength dispersive method for analyzing a sample using x-rays, comprising: exposing the sample to focused x-rays to cause at least one component of the sample to x-ray fluoresce, including: focusing the x-rays on the sample with a first focusing optic, into at least one x-ray exposure chamber, having an exposure aperture less than about 10 mm in diameter; and analyzing x-ray fluorescence to determine at least one characteristic of the sample, including: using at least one x-ray detector having an active area operating at a temperature greater than about 0 degrees centigrade and substantially uncooled, and collecting x-ray fluorescence from the sample and focusing said x-ray fluorescence on the detector, using a second focusing optic; wherein at least one of the first or second focusing optics is a monochromating optic providing wavelength dispersion for the focused x-rays and/or the x-ray fluorescence from the sample.

19. The method of claim 18, wherein the at least one characteristic of the sample comprises a concentration of at least one component in the sample.

20. The method of claim 19, wherein the sample is fuel, arid the at least one characteristic is the concentration of sulfur in the fuel.

21. The method of claim 18, wherein the detector comprises at least one semiconductor-type x-ray detector.

22. The method of claim 21, wherein the detector comprises at least one PIN-diode-semiconductor-type x-ray detector.

23. The method of claim 21, wherein the semiconductor-type x-ray detector comprises a detector active area having an area less than about 10 square millimeters.

24. The method of claim 23, wherein the semiconductor-type x-ray detector comprises a detector active area having an area less than about 6 square millimeters.

25. The method of claim 21, wherein the detector has no protective window.

26. The method of claim 18, wherein the x-rays are transmitted through a chamber held under vacuum.

27. The method of claim 18, wherein the x-ray exposure aperture is less than about 5 mm in diameter.

28. The method of claim 18, wherein the sample comprises a continuous, pressurized fluid stream, the apparatus further comprising: delivering the continuous fluid stream for said analyzing.

29. The method of claim 18, wherein at least one of the focusing optics comprises a polycapillary focusing optic.

30. The method of claim 18, wherein at least one of the focusing optics comprises a curved crystal monochromating optic.

31. The method of claim 30, wherein both focusing optics comprise doubly curved crystal monochromating optics.

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Description

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TECHNICAL FIELD

This invention relates generally to apparatus and methods used for x-ray fluorescence analysis, for example, x-ray fluorescence analysis of fluid streams. Specifically, the present invention provides improved methods and apparatus for detecting the presence of sulfur in fluid fuel streams; with improved methods and apparatus for removing heat from high-power, high-voltage electrical components, and including enhanced stability over a range of operating conditions.

BACKGROUND OF THE INVENTION

The implementation of x-ray analysis methods has been one of the most significant developments in twentieth-century science and technology. The use of x-ray diffraction, x-ray spectroscopy, x-ray imaging, and other x-ray analysis techniques has led to a profound increase in knowledge in virtually all scientific fields.

X-ray fluorescence (XRF) is an analytical technique by which a substance is exposed to a beam of x-rays to determine, for example, the presence of certain chemicals. In the XRF technique, at least some of the chemical constituents of the substance exposed to x-rays can absorb x-ray photons and produce characteristic secondary fluorescence x-rays. These secondary x-rays are characteristic of the chemical constituents in the substance. Upon appropriate detection and analysis these secondary x-rays can be used to characterize one or more of the chemical constituents of the substance. The XRF technique has broad applications in many chemical and material science fields, including medical analysis, semiconductor chip evaluation, and forensics, among others.

XRF methods have often been used for measuring the sulfur content of fuels, for example, petroleum-based fuels, such as gasoline and diesel fuels. Existing XRF systems have been known to detect sulfur in fuels down to as low as 5 parts per million (ppm) by weight; however, this detectability has required stringent control conditions, for example, this detectability is typically achievable only in the laboratory. Under less rigorous conditions, for example, in the field, existing XRF methods, such as ASTM standard method D2622, are limited to detecting sulfur concentrations in fuels only down to about 30 ppm. Among other things, the present invention provides improvements in repeatability and detectability of XRF detection of sulfur in fuels.

In these and many other industries, for example, the analytical industry, x-ray beam generating devices are commonly used. X-ray beam generating devices may typically include x-ray tubes which generate x-rays by impinging electron beams onto metal surfaces. X-ray tubes typically include an electron gun which generates an electron beam and an anode which provides the metal surface upon which the electron beam is directed. Typically, the electron gun and anode are operated in three different modes: 1) with a grounded anode and the electron gun operated at high positive voltage; 2) with a grounded electron gun (that is, a grounded cathode) and the anode operated at high negative voltage; or 3) in a "bi-polar" mode with cathode and anode operated at different voltages. For low power applications, the x-ray tube is typically operated with a "grounded cathode" wherein the electron gun and its adjacent components are operated at essentially ground potential and the anode and its adjacent components, if any, at high electric potential, for example, at 50 kilovolts (kv) or higher.

The impingement of the electron beam on the anode and the operation of the anode at such high voltages generates heat, typically a lot of heat, for example, at least about 50 Watts. In order to dissipate this heat, an x-ray tube is typically immersed in a cooling fluid, that is, a thermally-conductive cooling fluid, such as a cooling oil having a high enough dielectric strength to prevent the cooling oil from breaking down and permitting arcing at high potential. A typical high-dielectric cooling fluid is Diala Ax oil provided by Shell Oil Company.

In the conventional art, the x-ray tube and the cooling oil are typically held inside a sealed container, for example, a cylindrical metal container, wherein the x-ray tube is immersed in oil and electrically isolated from the container. The resulting structure includes an x-ray tube having a high-temperature anode at high potential surrounded by a high dielectric strength oil, all encased inside a sealed metal container. As a result, the oil typically convects inside the container as it is heated by the anode. This heating of the oil through convection also heats the walls of the container and the x-ray tube itself via convection. Conventionally, the outside walls of the sealed container may be cooled directly by, for example, natural convection, forced air convection, or flowing a cooling fluid over the outside of the container. This chain of convective and conductive heat transfer is an inefficient cooling process. Even for a conventional x-ray tube requiring modest power dissipation, the x-ray beam device and its components typically reach high temperatures, for example, as much as 120 degrees C. Such high temperatures are undesirable and can be detrimental to the operation of the x-ray tube.

Thus, there is a need in the art to provide simplified methods for cooling an x-ray beam device, or any other high-temperature, high voltage devices.

Moreover, the ability to focus x-ray radiation, until recently unachievable, has enabled reductions in the size and cost of x-ray sources, and hence x-ray systems, that find use in a variety of applications. U.S. Pat. No. 6,351,520 describes one example of an x-ray source which includes a focusing element that enables the production of a high intensity, small diameter x-ray spot size while incorporating a low-power, reduced-cost x-ray source.

While progress in the ability to focus x-ray radiation has recently been achieved, there remains a need for further enhancements to x-ray source assemblies, for example, to improve output stability of an x-ray beam under a variety of operating conditions. The present invention is directed to meeting this need.

SUMMARY OF THE INVENTION

The present invention provides methods and apparatus which address many of the limitations of prior art methods and apparatus. In the following description, and throughout this specification, the expressions "focus", "focusing", and "focused", among others, repeatedly appear, for example, as in "focusing device", "x-ray focusing device", "means for focusing", "focusing optic", among others. Though according to the present invention these expressions can apply to devices or methods in which x-rays are indeed "focused", for example, caused to be concentrated, these expressions are not meant to limit the invention to devices that "focus" x-rays. According to the present invention, the term "focus" and related terms are intended to also serve to identify methods and devices which collect x-rays, collimate x-rays, converge x-rays, diverge x-rays, or devices that in any way vary the intensity, direction, path, or shape of x-rays. All these means of handling, manipulating, varying, modifying, or treating x-rays are encompassed in this specification by the term "focus" and its related terms.

One aspect of the present invention is an x-ray tube assembly comprising: an x-ray tube; and a thermally-conductive, dielectric material thermally coupled to the x-ray tube for removing heat generated by the x-ray tube. The thermally-conductive, dielectric material may be aluminum nitride, beryllium oxide, and diamond-like carbon, among others. The x-ray tube assembly may include an x-ray tube having a first end and a second end, and the first end of the x-ray tube including an electron beam generator and the second end of the x-ray tube including an anode having a surface upon which the electron beam is impinged to generate a source of x-rays. The thermally-conductive, dielectric material is typically thermally coupled to the anode. Cooling means may also be thermally coupled to the thermally-conductive, dielectric material, for example, at least one cooling fin or cooling pin. In one aspect of the invention, sufficient heat may be removed from the x-ray tube by means of the thermally-conductive, dielectric material whereby the x-ray tube assembly may be air cooled. In one aspect of the invention, sufficient heat may be removed from the x-ray tube by means of the thermally-conductive, dielectric material whereby the x-ray tube is not contacted with a fluid coolant.

Another aspect of the invention comprises a method of operating an x-ray tube assembly having an electron beam generator and an anode, comprising: directing a beam of electrons from the electron beam generator to the anode to generate x-rays and thereby heat the anode; providing a thermally-conductive, dielectric material thermally coupled with the anode, and conducting heat from the anode by means of the thermally-conductive, dielectric material. Again, the thermally-conductive, dielectric material may be aluminum nitride, beryllium oxide, or diamond-like carbon, among others. In one aspect, the anode is electrically isolated and little or no electrons pass from the anode to the thermally-conductive, dielectric material. In one aspect of this method, sufficient heat may be removed from the anode when conducting heat from the anode by means of the thermally-conductive, dielectric material whereby the x-ray tube assembly may be air cooled. In one aspect of this method, sufficient heat may be removed from the anode when conducting heat from the anode by means of the thermally-conductive, dielectric material whereby the x-ray tube is not contacted with a fluid coolant.

Another aspect of the invention comprises an x-ray source assembly, comprising: a housing; an x-ray tube for generating x-rays, the x-ray tube being mounted in the housing; a thermally-conductive, dielectric material thermally coupled to the x-ray tube for removing heat generated by the x-ray tube; and at least one perforation in the housing for emitting x-rays generated by the x-ray tube. The x-ray source assembly may further include means for adjustably mounting the x-ray tube in the housing. In one aspect, the x-ray source assembly includes an x-ray tube having a first end and a second end and the first end of the x-ray tube comprises an electron beam generator and the second end of the x-ray tube comprises a surface upon which the electron beam is impinged to generate the x-rays. Again, the thermally-conductive, dielectric material may be aluminum nitride, beryllium oxide, or diamond-like carbon, among others. The dielectric material may also be cooled by at least one cooling fin or cooling pin thermally coupled to the thermally-conductive, dielectric material. The x-ray source assembly may also have an x-ray source which is adjustably mounted to the x-ray tube housing, for example, by at least one threaded pin. The x-ray source assembly may also include means for varying or modifying the x-rays emitted through the at least one perforation in the housing, for example, by means of a moveable baffle with at least one perforation. In one aspect of the invention, an x-ray optic may be mounted to receive at least some x-rays emitted through the at least one perforation in the housing. In one aspect of this assembly, sufficient heat may be removed from the x-ray tube by means of the thermally-conductive, dielectric material whereby the x-ray tube assembly may be air cooled. In one aspect of this assembly, sufficient heat may be removed from the x-ray tube by means of the thermally-conductive, dielectric material whereby the x-ray tube is not contacted with a fluid coolant.

Another aspect of the present invention comprises a method of operating an x-ray tube assembly having a first end comprising an electron beam generator and a second end having an anode and a thermally-conductive, dielectric material thermally coupled with the anode, comprising: directing a beam of electrons from the electron beam generator to the anode to provide x-rays and thereby heat the anode; and cooling the anode by conducting heat from the anode to the thermally-conductive, dielectric material. The x-ray tube assembly may also include at least one cooling pin or cooling fin and cooling the anode may further include passing a fluid coolant over the at least one cooling pin or cooling fin. Also, the cooling of the anode by conducting heat from the anode to the thermally-conductive, dielectric material may be practiced while passing little or no electrons from the anode. In one aspect of this method, sufficient heat may be removed from the anode when cooling the anode by conducting heat from the anode by means of the thermally-conductive, dielectric material whereby the x-ray tube assembly may be air-cooled. In another aspect of this method, sufficient heat may be removed from the anode when cooling the anode by conducting heat from the anode by means of the thermally-conductive, dielectric material whereby the x-ray tube is not contacted with a fluid coolant.

Another aspect of the present invention comprises a method for optimizing transmission of x-rays from an x-ray source and an x-ray focusing device wherein the x-ray source comprises an x-ray tube for generating x-rays, the x-ray tube being mounted in a housing by adjustable mounting means, and the housing having at least one perforation for emitting x-rays generated by the x-ray tube, the method comprising: mounting the x-ray tube in the housing; energizing the x-ray tube whereby a beam of x-rays is emitted through the at least one perforation in the housing; mounting the x-ray focusing device adjacent to the at least one perforation in the housing whereby the x-ray focusing device receives at least some x-rays from the x-ray tube; and adjusting the adjustable mounting means of the x-ray tube to optimize transmission of x-rays through the x-ray focusing device. The adjustable mounting means may comprise a plurality of threaded fasteners. The x-ray focusing device may comprise an x-ray focusing crystal or an x-ray focusing capillary device.

A further aspect of the present invention is an x-ray fluorescence analysis system, comprising: an x-ray source assembly having an x-ray source and a housing; a first x-ray focusing device operatively connected to the x-ray source assembly and having means for aligning the first x-ray focusing device with the x-ray source assembly; an x-ray exposure assembly having a housing operatively connected to the x-ray focusing device and having means for aligning the x-ray exposure assembly with the first x-ray focusing device; a second x-ray focusing device operatively connected to the x-ray exposure assembly and having means for aligning the second x-ray focusing device with the x-ray exposure assembly; and an x-ray detection device operatively connected to the second x-ray focusing device and having means for aligning the x-ray detection device with the second x-ray focusing device; wherein at least one of the means for aligning comprises a plurality of alignment pins. The alignment of at least one of the assemblies, preferably a plurality of assemblies, permits one or more of the assemblies to be assembled off site and installed on site without requiring extensive realignment of the assemblies on site. Avoiding realignment on site is more efficient.

Another aspect of the present invention is a method of detecting x-rays, comprising: providing a source of x-rays; focusing at least some of the x-rays using an x-ray optic on a small-area x-ray detector; and detecting the x-rays by means of the small-area x-ray detector. In one aspect of the invention, the small-area detector may be may be a semiconductor-type detector or a silicon-lithium-type detector (that is, a SiLi-type detector). In one aspect of the invention, the small-are detector may be a PIN-diode-type detector. One aspect of the invention further comprises cooling the small-area detector, for example, air-cooling the small-area detector. The small-area ray detector may include a detector aperture and the detector aperture area may be less than about 10 square millimeters, preferably, less than about 6 square millimeters, or even less than about 4 square millimeters. The focusing of at least some of the x-rays may be practiced using a capillary-type x-ray optic or a DCC x-ray optic. The method may be practiced at a temperature greater than about 0 degrees centigrade, for example, at a temperature between about 10 degrees centigrade and about 40 degrees centigrade.

A further aspect of the invention comprises a device for detecting x-rays, comprising: a small-area x-ray detector; and means for focusing at least some of the x-rays on small-area x-ray detector. The small-area x-ray detector typically includes a detector aperture having an area less than about 10 square millimeters, typically, less than about 6 square millimeters. The small-area x-ray detector may be a semiconductor-type detector or a silicon-lithium-type detector. In one aspect of the invention the small-area detector may be a PIN-diode-type. In one aspect of the invention, the small-area detector may be cooled, for example, air-cooled. The means for focusing at least some x-rays may comprise an x-ray optic, for example, a curved-crystal or capillary x-ray optic.

Another aspect of the invention comprises an apparatus for analyzing a fluid using x-rays, comprising: means for exposing the fluid to x-rays to cause at least one component of the fluid to x-ray fluoresce; and means for analyzing the x-ray fluorescence from the fluid to determine at least one characteristic of the fluid. The fluid may be a liquid or a gas. The means for exposing the fluid to x-rays may be at least one x-ray optic for focusing x-rays on the fluid.

Another aspect of the present invention comprises a method for analyzing components in a fluid using x-rays, comprising: exposing the fluid to x-rays to cause at least one component in the fluid to x-ray fluoresce; detecting the x-ray fluorescence from the fluid; and analyzing the detected x-ray fluorescence to determine at least one characteristic of the fluid. According to one aspect, the method is practiced essentially continually for a period of time. The method may also be practiced under vacuum.

In one aspect, the detecting of the x-ray fluorescence is practiced at a temperature greater than about minus 50 degrees centigrade, for example, at greater than about 0 degrees centigrade. In another aspect of the method, the detecting of the x-ray fluorescence may be practiced using a small-area x-ray detector, for instance, a semiconductor-type x-ray detector, for example, a PIN-type semiconductor x-ray detector.

Another aspect of the present invention comprises an apparatus for analyzing sulfur in a fuel, comprising: means for exposing the fuel to x-rays to cause at least some sulfur in the fuel to x-ray fluoresce; and means for analyzing the x-ray fluorescence from the fuel to determine at least one characteristic of the sulfur in the fuel. The at least one characteristic of the sulfur in the fuel may be the concentration of sulfur in the fuel.

A still further aspect of the present invention is a method for analyzing sulfur in a fuel, comprising: exposing the fuel to x-rays to cause at least some of the sulfur in the fuel to x-ray fluoresce; detecting the x-ray fluorescence; and analyzing the x-ray fluorescence from the sulfur to determine at least one characteristic of the sulfur in the fuel. The method is typically practiced essentially continually for a period of time. The exposing of the fuel to x-rays may be practiced under vacuum. When practiced under vacuum, the fuel will typically be enclosed in a chamber to prevent exposure to the vacuum, for example, the fuel may be enclosed in a chamber and the x-rays access the fuel via a window in the chamber. According to one aspect, the x-rays may be monochromatic x-rays. Also, the detecting of the x-ray fluorescence may be practiced at a temperature greater than about minus 100 degrees centigrade, typically greater than about minus 50 degrees centigrade, or even greater than about 0 degrees centigrade, for example at about room temperature (20 degrees centigrade). The detecting may be practiced using a semiconductor-type detector, for example, a PIN-type semiconductor detector.

Regarding improved heat dissipating aspects of the invention, the invention is a device for cooling and electrically-insulating a high-voltage, heat-generating component. This device includes: a first thermally-conductive material having a first side in thermal communication with the component and a second side; a thermally-conductive dielectric material having a first side in thermal communication with the second side of the first thermally-conductive material and a second side; and a second thermally-conductive material having a first side in thermal communication with the second side of the thermally-conductive, dielectric material; wherein heat generated by the component is conducted away from the component through the device while current loss across the device is minimized. In one aspect of the invention, the thermal communication between the component and the first thermally-conductive material is through an area of contact between the component and the first thermally-conductive material, the area of contact having a first outer dimension, and wherein the first thermally-conductive material comprises a periphery having a second outer dimension, greater than the first outer dimension, wherein at least some heat from the component is conducted in the first thermally-conductive material in a direction from the area of contact toward the periphery of the first thermally-conductive material. In another aspect of the invention, the first thermally-conductive material comprises a first plate, wherein at least some heat is conducted in the first plate in a direction from the area of contact toward the periphery of the first plate, and hence through the thermally-conductive dielectric material to the second thermally-conductive material. The invention may also include means for facilitating removal of heat from the second thermally-conductive material, for example, at least one cooling fin or cooling pin. In one aspect of the invention, the thermally-conductive dielectric material comprises one of aluminum nitride, beryllium oxide, and diamond-like carbon. The high-voltage, heat-generating component may be an x-ray generator, an electron-beam generator, a high-voltage lead, or a microwave generator, among other devices.

This aspect of the invention may be used with the fluid-analyzing technique and optics discussed above.

Another aspect of the heat dissipating invention is an x-ray tube assembly including: an x-ray tube comprising a high-voltage, heated anode; and a heat dissipating device coupled to the anode, the heat dissipating device comprising: a first metal plate having a first side in thermal communication with the anode and a second side; a thermally-conductive dielectric material plate having a first side in thermal communication with the second side of the first metal plate and a second side; and a second metal plate having a first side in thermal communication with the second side of the thermally-conductive dielectric material plate; wherein heat generated in the anode is conducted away from the anode through the device while current loss across the device is minimized. In one enhanced aspect of the invention, the heat dissipating device provided structural support for the anode, for example, the heat dissipating device can provide essentially all the structural support for the anode. In another aspect of the invention, the x-ray tube assembly further includes a high voltage connector coupled with the first metal plate.

This aspect of the invention may be used with the fluid-analyzing technique and optics discussed above.

A further aspect of the heat dissipation invention is a method for fabricating a device for cooling and electrically-insulating a high-voltage, heat-generating component, the method comprising: providing a first thermally-conductive material having a first surface for contacting the component and a second surface; providing a thermally-conductive dielectric material having a first surface and a second surface; coupling the first surface of the first thermally-conductive dielectric material to the second surface of the first thermally-conductive material, so that the first thermally-conductive material and the thermally-conductive dielectric material are in thermal communication; providing a second thermally-conductive material having a first surface and a second surface; and coupling the first surface of the second thermally-conductive material to the second surface of the thermally-conductive dielectric material so that the thermally-conductive dielectric material and the second thermally-conductive material are in thermal communication. In one aspect of the invention, coupling comprises, gluing, adhesive bonding, soldering, brazing, or welding. One adhesive that may be used is Dow Chemical's 4174 thermally-conductive, silicone adhesive, or its equivalent. Another aspect of the invention further includes coupling a high voltage connector to the electrically-conductive, first thermally-conductive material.

This aspect of the invention may be used with the fluid-analyzing system and optics discussed above.

Since it may be desirable to align the x-ray beam produced by an x-ray device with an internal or external x-ray optic, according to one aspect of the invention, the components of an x-ray beam device are mounted in a way that enables the user to adjust the position or direction of the x-ray beam relative to an optic to account for, among other things, variations in alignment due to thermal expansion. Furthermore, since the alignment of an x-ray beam device with an optic can be difficult when the x-ray tube is bolted inside a sealed container and the sealed container contains a cooling fluid, in one aspect of the invention, x-ray beam device is provided which requires little or no cooling fluid. For example, according to one aspect of the invention, an x-ray beam device is provided having sufficient cooling yet permitting alignment of the device, for example, precise alignment with an optical device.

This aspect of the invention may be used with the fluid-analyzing system and optics discussed above.

Regarding the enhanced stability aspects of the invention, the use of e-beam impingement upon an anode to generate x-rays, such as in the x-ray tubes described above, can generate an amount of heat that is sufficient to cause thermal expansion of the elements which support and position the x-ray tube within the x-ray source. This thermal expansion can be sufficient to cause a misalignment between the x-rays that are diverging from the anode and, e.g., the element that serves to control the direction of the x-rays. As a result, operating an x-ray source at different powers may lead to a range of misalignments between the diverging x-rays and the focusing electrode. This misalignment could cause the output power intensity of the x-ray source to vary widely. Misalignment could also cause changes in x-ray spot or x-ray beam position for some types of beam controlling elements, e.g., for pinholes or single reflection mirrors. Thus, in one aspect, provided herein is an x-ray source assembly having enhanced output stability over a range of operating power levels, as well as enhanced x-ray spot or x-ray beam position stability. More particularly, an x-ray source assembly in accordance with an aspect of the present invention provides an x-ray beam output intensity which can be maintained relatively constant notwithstanding variation in one or more operating conditions of the x-ray source, such as anode power level, housing temperature and ambient temperature about the assembly.

This aspect of the invention may be used with the fluid-analyzing system, optics and heat dissipation aspects discussed above.

For enhanced stability, additional advantages are provided through the provision of an x-ray source assembly which includes an anode having a source spot upon which electrons impinge, and a control system for controlling position of the anode source spot relative to an output structure. The control system can maintain the anode source spot location relative to the output structure notwithstanding a change in one or more operating conditions of the x-ray source assembly.

This aspect of the invention may be used with the fluid-analyzing system, optics and heat dissipation aspects discussed above.

In another enhanced stability aspect of the invention, an x-ray source assembly is provided which includes an x-ray tube having an anode for generating x-rays, and an optic for collecting x-rays generated by the anode. The x-ray source assembly further includes a control system for controlling x-ray output intensity of the optic. The control system can maintain x-ray output intensity notwithstanding a change in one or more operating conditions of the x-ray source assembly.

This aspect of the invention may be used with the fluid-analyzing system, optics and heat dissipation aspects discussed above.

In still another enhanced stability aspect of the invention, a method of providing x-rays is presented which includes: providing an x-ray source assembly having an anode with a source spot upon which electrons impinge; and controlling position of the anode source spot relative to an output structure, wherein the controlling includes maintaining the anode source spot location relative to the output structure notwithstanding a change in at least one operating condition of the x-ray source assembly.

This aspect of the invention may be used with the fluid-analyzing system, optics and heat dissipation aspects discussed above.

In a further enhanced stability aspect of the invention, a method of providing x-rays is presented which includes: providing an x-ray source assembly having an x-ray tube with an anode for generating x-rays and an optic for collecting x-rays generated by the anode; and controlling x-ray output intensity from the optic, wherein the controlling includes maintaining x-ray output intensity from the optic notwithstanding a change in at least one operating condition of the x-ray source assembly.

This aspect of the invention may be used with the fluid-analyzing system, optics and heat dissipation aspects discussed above.

These and other embodiments and aspects of the present invention will become more apparent upon review of the attached drawings, description below, and attached claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of practice, together with further objects and advantages thereof, may best be understood by reference to the following detailed descriptions of the preferred embodiments and the accompanying drawings in which:

FIG. 1 is a schematic block diagram of an x-ray fluorescence system that can be used to practice the present invention.

FIG. 2 is a schematic cross-sectional view of a prior art x-ray tube over which one aspect of the present invention is an improvement.

FIG. 3 is a schematic cross-sectional view of one aspect of the present invention.

FIGS. 4, 5, and 6 illustrate various perspective views of another aspect of the present invention.

FIG. 7 is a perspective view of the housing assembly of another aspect of the present invention.

FIG. 8 is a perspective view of the aspect of the invention shown in FIG. 7 with the housing removed.

FIG. 9 is a schematic block diagram of an x-ray fluorescence system according to another aspect of the present invention.

FIG. 10 illustrates a cross-sectional elevation view of one embodiment of a high-voltage component and a cooling and electrically-insulating device in accordance with one aspect of the present invention.

FIG. 11 illustrates a detail of the cooling and electrically-insulating device of FIG. 10 in accordance with one aspect of the present invention.

FIG. 12 depicts a cross-sectional view of one embodiment of an x-ray source assembly, in accordance with an aspect of the present invention;

FIG. 13 depicts one example of a source scan curve for an x-ray source such as shown in FIG. 12 plotting output intensity versus displacement, in accordance with an aspect of the present invention;

FIG. 14 depicts a cross-sectional view of the x-ray source assembly of FIG. 1 showing a source spot to optic misalignment, which is addressed in accordance with an aspect of the present invention;

FIG. 15 depicts a cross-sectional view of the x-ray source assembly of FIG. 14 showing different sensor placements for monitoring source spot to optic displacement, in accordance with an aspect of the present invention;

FIG. 16 is a cross-sectional view of one embodiment of the anode base assembly depicted in FIGS. 12, 14 & 15, in accordance with an aspect of the present invention;

FIG. 17 is a cross-sectional view of the anode stack of FIGS. 12, 14 & 15, in accordance with an aspect of the present invention;

FIG. 17A is a graphical representation of change in temperature across the elements of the anode stack for different anode power levels, in accordance with an aspect of the present invention;

FIG. 17B is a graph of change in reference temperature as a function of anode power level, in accordance with an aspect of the present invention;

FIG. 18 depicts a cross-sectional view of one embodiment of an enhanced x-ray source assembly, in accordance with an aspect of the present invention;

FIG. 19 depicts a block diagram of one embodiment of a control system for an x-ray source assembly, in accordance with an aspect of the present invention;

FIG. 19A is a representation of one embodiment of processing implemented by the processor of the control system of FIG. 19, in accordance with an aspect of the present invention;

FIG. 20 is a flowchart of one embodiment of control processing for an x-ray source assembly, in accordance with an aspect of the present invention; and

FIG. 21 is an exemplary reference temperature table which can be employed by the control processing of FIG. 20, in accordance with an aspect of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a schematic block diagram of a typical system 10 used for exposing a substance to x-ray radiation to produce flourescent radiation which can then be detected and analyzed to determine a characteristic of the substance. Such a system typically includes an x-ray source 12, a first x-ray focusing device 14, a sample excitation chamber 16, a second x-ray focusing device 18, and an x-ray detector 20. The x-ray source 12, for example, an x-ray tube, produces a beam of x-rays 22. Since x-ray beam 22 is typically a divergent beam, beam 22 is diffracted or focused by means of one or more x-ray focusing devices 14. X-ray focusing device 14 may be one or more doubly-curved crystals, for example, a doubly-curved crystal having essentially parallel atomic planes, such as the crystals disclosed in pending application Ser. No. 09/667,966 filed on Sep. 22, 2000, the disclosure of which is incorporated by reference herein. X-ray focusing device may be one or more capillary-type x-ray optic or curved crystal optic, for example, one of the optics disclosed in U.S. Pat. Nos. 6,317,483; 6,285,506; 5,747,821; 5,745,547; 5,604,353; 5,570,408; 5,553,105; 5,497,008; 5,192,869; and 5,175,755, the disclosures of which are incorporated by reference herein. The one or more x-ray focusing devices produces a focused beam 24 directed toward the sample excitation chamber 16.

The sample under test in excitation chamber 16 may be any desired substance for which a characteristic is desired. The sample may be a solid, a liquid or a gas. If the sample is a solid, the sample is typically located on a relatively flat surface, for example, an x-ray reflective flat surface, for example, an optically-reflective surface. The sample, if a solid, liquid, or gas, may also be contained in a closed container or chamber, for example, a sealed container, having a x-ray transparent aperture through which x-ray beam can pass. When irradiated by beam 24, at least one of the constituents of sample in chamber 16 typically is excited in such a fashion that the constituent x-ray fluoresces, that is, produces a secondary source of x-rays 26 due to excitation by x-rays 24. Again, since x-ray beam 26 is typically a diverging beam of x-rays, beam 26 is focused by means of the second x-ray focusing device 18, for example, a device similar to device 14, to produce a focused beam of x-rays 28 directed toward x-ray detector 20. It will be apparent to those of skill in the art that this and other aspects of the present invention, though described with respect to x-ray fluorescence applications, may also be utilized in x-ray absorption applications.

X-ray detector 20 may be a proportional counter-type or a semiconductor type x-ray detector. Typically, x-ray detector 20 produces an electrical signal 30 containing at least some characteristic of the detected x-rays which is forwarded to an analyzer 32 for analysis, printout, or other display.

Various aspects of the present invention provide advancements and improvements to the system 10 and system components shown in FIG. 1. One of these aspects of the present invention is disclosed with respect to FIGS. 2 and 3. FIG. 2 illustrates a cross-section of a typical prior art x-ray tube assembly 34, for example, a Series 5000 TF5011 x-ray tube produced by Oxford Instruments of Scotts Valley, Calif., though other similar x-ray tubes may be used. As is typical, this prior art x-ray tube 34 includes a cylindrical housing 36, which typically comprises a non-conducting glass housing. An electron-beam generator 38 and an anode 40 are mounted in housing 34 typically in the orientation shown. Anode 40 is typically a thin solid material, for example, tungsten or Chromium mounted on a conducting anode of copper or a similar high-thermal-conductivity material. Anode 40 is typically fashioned to provide surface 50 and having cylindrical support structure 41 fashioned to provide a rigid support for anode 40 in housing 41 and also to isolate the gas volume above structure 41 from the volume below structure 41. Anode 40 also includes a cylindrical non-conducting support 44 which penetrates housing 36. Electrical connections 42 provide power to the electron-beam generator 38. Housing 36 typically includes at least one aperture 46 for emitting the x-rays produced by x-ray tube 34. Housing 36 typically isolates the internal volume of tube 34 from the ambient environment and the internal volume of tube 34 is typically provided with at least some form or vacuum, for example, about 10.sup.-6 Torr.

When power, for example, 50 Watts, is provided to electrical connections 42, electron-beam generator 38 produces a beam of electrons, as indicated by arrow 48, directed towards surface 50 of anode 40. Surface 50 is typically an inclined surface, for example, inclined at about 45 degrees to the axis of the tube. The interaction of electron beam 48 with surface 50 produces x-rays which are scattered in all directions. The wavelength and frequency of the x-rays produced is a function of the power provided to electrical connections 42, among other things. However, at least one path of these scattered x-rays is indicated by arrow 52 directed toward aperture 46. The direction of x-ray beam 52 is a typically a function of the orientation of tube 34. The x-ray beam represented by arrow 52 passes through x-ray permeable barrier 54 in aperture 46. The x-ray permeable barrier 54 is typically made from beryllium (Be) or titanium (Ti) which permits the passage of x-rays while isolating the internal volume of the housing 36 from the ambient environment.

The generation of x-rays by the impingement of electron beam 48 upon anode 40 generates substantial heat, for example, the temperature of anode 40 typically is elevated to a least 60 degrees centigrade, and can reach as high as the melting point of tungsten. In consequence, tube 34 is typically immersed in a cooling and insulating fluid 56, for example, an petroleum-based oil. Tube 34 and fluid 56 are typically contained in a cylindrical housing 58. Housing 58 is typically impermeable to x-rays, for example, housing 58 can be typically lead-lined. The volume of cooling and insulating fluid 56 and thus the size of housing 58 is a function of the cooling requirements of x-ray tube 34. Housing 58 also typically includes an aperture 60 aligned with aperture 46 of tube 34 to emit x-rays generated by tube 34. Tube 34 is typically rigidly mounted within housing 58 by means of a supporting structure 62 attached to support 44 of tube 34, for example, by means of a threaded connection. Support 44 is typically made of a non-conducting material, for example, a ceramic material, to electrically isolate anode 40 from housing 58.

FIG. 3 illustrates an x-ray tube assembly 64 according to one aspect of the present invention that is an improvement over the prior art x-ray tube assembly illustrated in FIG. 2. Many of the features that appear in FIG. 3 can be essentially identical to the features of FIG. 2 and are identified with the same reference numbers. According to this aspect of the present invention, x-ray tube assembly 64 includes an x-ray tube 34' (which may be similar to tube 34) having a housing 36, an electron-beam generator 38, an anode 40, and an aperture 46 essentially identical to the structures illustrated and described with respect to FIG. 2. However, according to the present invention, x-ray tube assembly 64 includes at least one thermally-conducting, but non-electrically conducting material 70 mounted or thermally coupled to x-ray tube 34'. The thermally-conducting, non-electrically conducting material (which may be referred to as a thermally-conducting, dielectric material) 70 is a material having a high thermal conductivity and also a high dielectric strength. For example, material 70 typically has a thermal conductivity of at least about 100 Wm-1K-1, and preferably at least 150 Wm.sup.-1K.sup.-1; and material 70 typically has a dielectric strength of at least about 1.6.times.10.sup.7Vm.sup.-1, preferably at least about 2.56.times.10.sup.7Vm.sup.-1. Material 70 may be aluminum nitride, beryllium oxide, diamond-like carbon, a combination thereof, or equivalents or derivatives thereof, among others. In FIG. 3, material 70 is illustrated as a cylindrical structure, for example, a circular cylindrical or rectangular cylindrical structure, though material 70 may take many difference geometrical shapes and provide the desired function.

X-ray tube 64 may typically mounted in a housing 158. Housing 158, like housing 58 in FIG. 2 is typically fabricated from an x-ray impermeable material, for example, a lead-lined material, lead, or tungsten. Housing 158 may assume any appropriate shape, including circular cylindrical and rectangular cylindrical. In one aspect of the invention, housing 158 is fabricated from tungsten plate, and due to the poor machinability of tungsten, housing 158 is preferably rectangular cylindrical in shape. Of course, should methods be produced for providing other means of fabricating tungsten housings, these can also be applied to the present invention.

According to the present invention, thermally-conducting, dielectric material 70 permits the conducting of heat away from anode 40 specifically and tube 34' in general while minimizing or preventing the passage of electrical current from anode 40 specifically and tube 34' in general. In this aspect of the invention, support 44' (unlike support 44 of tube 34 of FIG. 2) is typically made of a conducting material, for example, copper or aluminum. According to this aspect of the invention, heat is conducted away from anode 40 via support 44' and material 70 while material 70 electrically isolates anode 40 from, for example, an external housing 158.

Unlike prior art x-ray tube assemblies, the temperature of x-ray tube 34' according to this aspect of present invention can be reduced by conducting heat away from anode 40 and dissipating the heat to the adjacent environment via the surface area of material 70. Thus, material 70 cools anode 40 specifically and tube 34' in general such that the cooling requirements for tube 34' are reduced, or increased heating of anode 40 can be achieved. For example, in one aspect of the invention, the presence of material 70 provides sufficient means for cooling tube 34' whereby little or no additional cooling means is required. In another aspect of the invention, the presence of material 70 provides sufficient means for cooling tube 34' whereby air cooling provides sufficient cooling of tube 34', for example, forced air cooling (though non-forced-air cooling characterizes one aspect of the invention). In another aspect of the invention, the presence of material 70 provides sufficient means for cooling tube 34' whereby less cooling and insulating fluid is required than the fluid required for prior art x-ray tube assemblies, for example, at least 10% less cooling fluid than prior art tube assemblies; typically, at least 20% less cooling fluid than prior art tube assemblies; preferably, at least 50% less cooling fluid than prior art tube assemblies.

According to one aspect of the present invention, the cooling capacity of material 70 is increased by increasing the surface area of material 70, for example, by means of introducing cooling fins or cooling pins to material 70. In another aspect of the invention, additional cooling capacity is obtained by introducing cooling fins or cooling pins to a structure thermally coupled to material 70. One such optional structure is illustrated in phantom in FIG. 3. FIG. 3 includes plate 72 mounted or otherwise thermally coupled to material 70. Plate 72, made of a thermally conductive material, for example copper or aluminum, may provide sufficient surface area for cooling. In this aspect of the invention, the surface area of the thermally-coupled structure is enhanced by the use of cooling pins or cooling fins 74. According to one aspect of the invention, plate 72 and fins 74 are comprised of a material that is thermally conductive so that heat can be conducted away from material 70, for example, a copper-, iron, or aluminum-based. In another aspect of the invention, plate 72 is fabricated from a material that is both thermally conductive and resistant to the penetration of x-rays, for example, tungsten-copper. The copper in tungsten-copper provides the conductivity desired while the tungsten provides the desired x-ray shielding. Other materials having the same or similar properties may be used for plate 72. When plate 72 is a duplex material like tungsten-copper, fins 70 may be simply a copper- or aluminum-based material.

FIGS. 4, 5, and 6 illustrate an x-ray source and x-ray focusing device assembly 80 and an x-ray source assembly 82 according to other aspects of the present invention. X-ray source and x-ray focusing device assembly 80 comprises x-ray source assembly 82 and x-ray focusing device 84. The x-ray focusing device 84 shown in FIG. 4 is a polycapillary x-ray optic as disclosed in above-referenced U.S. patents, but device 84 may be any type of x-ray focusing device, for example, the x-ray focusing crystals and capillary type optics discussed above. In one aspect of the invention x-ray source assembly 82 comprises at least one x-ray source 64 having a thermally-conductive dielectric material 70 as described and illustra