Patent Number: 
Section: claims

1. An X-ray fluorescence analyzer, comprising:an X-ray tube for emitting incident X-rays in the direction of a first optical axis,a slurry handling unit configured to maintain a constant distance between a sample of slurry and said X-ray tube,a first crystal diffractor located in a first direction from said slurry handling unit, said first crystal diffractor being configured to separate a predefined first wavelength range from fluorescent X-rays that propagate into said first direction, and configured to direct the fluorescent X-rays in the separated predefined first wavelength range to a first radiation detector, wherein:the first crystal diffractor comprises a pyrolytic graphite crystal that has a diffractive surface, andsaid first radiation detector is a solid-state semiconductor detector;characterized in thatthe diffractive surface of said pyrolytic graphite crystal is a simply connected surface; andthe crystal is the wavelength-dispersive component of the crystal diffractor. 2. The X-ray fluorescence analyzer according to claim 1, wherein the diffractive surface of said pyrolytic graphite crystal is curved in one direction only. 3. The X-ray fluorescence analyzer according to claim 1, wherein the first crystal diffractor comprises a substrate to which said pyrolytic graphite crystal is attached, and wherein a three-dimensional geometrical shape of the entity constituted by said pyrolytic graphite crystal and said substrate is that of a prism, one side face of which is cut away by the curved diffractive surface. 4. The X-ray fluorescence analyzer according to claim 1, wherein said first radiation detector is one of: a PIN di-ode detector, a silicon drift detector, a germanium detector, a germanium drift detector. 5. The X-ray fluorescence analyzer according to claim 1, wherein the first crystal diffractor comprises:a first slit on a first optical path between said slurry handling unit and said pyrolytic graphite crystal, anda second optical path between said pyrolytic graphite crystal and said first radiation detector. 6. The X-ray fluorescence analyzer according to claim 5, wherein:the diffractive surface of said pyrolytic graphite crystal is curved in one direction only, with a radius of curvature in a plane defined by said first and second optical paths, andsaid first slit is a linear slit oriented perpendicular against said plane. 7. The X-ray fluorescence analyzer according to claim 5, wherein:the diffractive surface of said pyrolytic graphite crystal is curved in two directions, forming a part of a toroidal surface, andsaid first slit is a curved slit with a first radius of curvature oriented perpendicular against said first optical path. 8. The X-ray fluorescence analyzer according to claim 5, wherein:the diffractive surface of said pyrolytic graphite crystal is curved in two directions, forming a part of a rotationally symmetric surface, the rotational axis of which is in the plane defined by said first and second optical paths, andsaid first slit is point-like. 9. The X-ray fluorescence analyzer according to claim 6, wherein:the first crystal diffractor comprises a second slit on said second optical path between said pyrolytic graphite crystal and said first radiation detector,a center point of said diffractive surface, said first slit, and said second slit are located on a Rowland circle the radius of which is R,a radius of curvature of said diffractive surface in the plane defined by said first and second optical paths is 2R, anda radius of curvature of reticular planes in said crystal is 2R; so that the first crystal diffractor has a Johann geometry. 10. The X-ray fluorescence analyzer according to claim 6, wherein:the first crystal diffractor comprises a second slit on said second optical path between said pyrolytic graphite crystal and said first radiation detector,a center point of said diffractive surface, said first slit, and said second slit are located on a Rowland circle the radius of which is R,a radius of curvature of said diffractive surface in the plane defined by said first and second optical paths is R, andthe radius of curvature of reticular planes in said crystal is 2R; so that the first crystal diffractor has a Johansson geometry. 11. The X-ray fluorescence analyzer according to claim 9, wherein R is at most 40 centimeters. 12. The X-ray fluorescence analyzer according to claim 6, wherein:said first crystal diffractor is enclosed in a casing delimited by a first planar surface and a second planar surface that is parallel to said first planar surface. 13. The X-ray fluorescence analyzer according to claim 6, comprising a plurality of other crystal diffractors in addition to said first crystal diffractor, each of said first and other crystal diffractors being located at a respective rotation angle around said first optical axis and each of said first and other crystal diffractors being configured to separate a predefined wavelength range from fluorescent X-rays that propagate into the respective direction, and configured to direct the fluorescent X-rays in the respective separated predefined wavelength range to a respective radiation detector. 14. The X-ray fluorescence analyzer according to claim 13, wherein:said plurality of other crystal diffractors comprises a second crystal diffractor comprising a second crystal, configured to direct the fluorescent X-rays in the respective separated second predefined wavelength range to a respective second radiation detector,said second crystal is of a material other than pyrolytic graphite, andsaid first and second crystal diffractors are con-figured to direct to their respective radiation detectors characteristic fluorescent radiation of a same element. 15. The X-ray fluorescence analyzer according to claim 14, wherein said second crystal is one of: a silicon dioxide crystal, a lithium fluoride crystal, an ammonium dihydrogen phosphate crystal, a potassium hydrogen phthalate crystal. 16. The X-ray fluorescence analyzer according to claim 14, wherein said second radiation detector is a gas-filled proportional counter. 17. The X-ray fluorescence analyzer according to claim 14, wherein said element is gold. 18. The X-ray fluorescence analyzer according to claim 14, wherein:said slurry handling unit is configured to maintain a planar surface of said sample of slurry on a side facing said X-ray tube,said first optical axis is at an oblique angle against said planar surface,said first crystal diffractor is located at that rotational angle around said first optical axis at which said planar surface of said sample covers the largest portion of a field of view of the first crystal diffractor, andsaid second crystal diffractor is located at another rotational angle around said first optical axis. 19. The X-ray fluorescence analyzer according to claim 6, wherein an energy resolution of said first radiation detector is better than 300 eV at a reference energy of 5.9 keV. 20. The X-ray fluorescence analyzer according to claim 6, wherein the in-put power rating of said X-ray tube is at least 400 watts. 21. The X-ray fluorescence analyzer according to claim 20, wherein the input power rating of said X-ray tube is at least 1 kilowatt, preferably at least 2 kilowatts, and more preferably at least 4 kilowatts. 22. The X-ray fluorescence analyzer according to claim 6, wherein the optical path between said X-ray tube and said slurry handling unit is direct with no diffractor therebetween. 23. The X-ray fluorescence analyzer according to claim 6, whereinthe X-ray tube comprises an anode for generating said incident X-rays, andsaid slurry handling unit is configured to maintain a shortest linear distance that is shorter than 50 mm, preferably shorter than 40 mm, and more preferably shorter than 30 mm between said sample of slurry and said anode. 24. The X-ray fluorescence analyzer according to claim 23, wherein said X-ray tube is an X-ray tube of the end window type. 25. The X-ray fluorescence analyzer according to claim 6, further comprising:an analyzer body,a front wall of said analyzer body,an opening in said front wall, anda holder for removably holding said slurry handling unit against an outer side of said front wall and aligned with said opening in said front wall. 26. The X-ray fluorescence analyzer according to claim 25, wherein said X-ray tube and said first crystal diffractor are both inside said analyzer body, on the same side of said front wall. 27. The X-ray fluorescence analyzer according to claim 6, comprising a filter plate on the optical path between said X-ray tube and said slurry handling unit. 28. The X-ray fluorescence analyzer according to claim 27, wherein said filter plate is located closer to said X-ray tube than to said slurry handling unit. 29. The X-ray fluorescence analyzer according to claim 6, comprising a calibrator plate and an actuator configured to controllably move said calibrator plate between at least two positions, of which a first position is not on the path of the incident X-rays and a second position is on the path of the incident X-rays and in a field of view of the first crystal diffractor.