Patent Number: 
Section: claims

1. A shutter arrangement, comprising:an opening in an housing for allowing X-rays to pass through the opening from an inner face to an outer face of the X-ray housing, the X-ray housing being substantially opaque to X-rays; anda shutter movable between a blocking position adjacent to the opening where it blocks the opening and an open position where it allows X-rays to pass through the opening;wherein the shutter is of tantalum, niobium or zirconium, or an alloy containing at least 80% of one of these elements and a further metal/element; andwherein the shutter is a block having a through hole through the block, the hole being aligned with the opening when the shutter is in the open position to allow X-rays to pass through the hole and the shutter blocking the opening when the shutter is in the blocking position. 2. A shutter arrangement according to claim 1 wherein the through hole through the block is sized to completely cover edges of the opening when the shutter is in the open position. 3. A shutter arrangement according to claim 1 wherein the shutter is arranged to slide laterally across the opening in the plane of the opening between the blocking position and the open position. 4. A shutter arrangement according to claim 1 wherein the X-ray housing contains an X-ray tube, the X-ray tube having a window for allowing X-rays to pass out of the tube,wherein the shutter in the blocking position is at a distance of not more than 20 mm from the window in the X-ray tube. 5. A shutter arrangement according to claim 4, wherein the shutter in the blocking position is at a distance of not more than 10 mm from the window in the X-ray tube. 6. A shutter arrangement according to claim 1 wherein the housing is of brass. 7. A shutter arrangement according to claim 1 wherein the shutter consists essentially of tantalum. 8. A shutter arrangement according to claim 1 wherein the shutter consists of an alloy of at least 80% tantalum, niobium or zirconium and no more than 20% of at least one other metal/element having an atomic number of over 26. 9. A shutter arrangement according to claim 1 further comprising an X-ray transparent window sealing the opening. 10. A shutter arrangement, comprisingan opening in an housing for allowing X-rays to pass through the opening from an inner face to an outer face of the X-ray housing, the X-ray housing being substantially opaque to X-rays; anda shutter movable on the inner face of the X-ray housing between a blocking position adjacent to the opening where it blocks the opening and an open position where it allows X-rays to pass through the opening;wherein the shutter is of tantalum, niobium or zirconium, or an alloy containing at least 80% of one of these elements and a further metal/element. 11. A shutter arrangement according to claim 10, wherein the shutter is a block having a hole through the block, the hole being aligned with the opening when the shutter is in the open position to allow X-rays to pass through the hole and the shutter blocking the opening when the shutter is in the blocking position. 12. A shutter arrangement according to claim 11 wherein the hole through the block is sized so that all edges of the opening are completely covered when the shutter is in the open position. 13. A shutter arrangement according to claim 10 wherein the shutter is arranged to slide laterally across the opening in the plane of the opening between the blocking position and the open position. 14. A shutter arrangement according to claim 10 wherein the X-ray housing contains an X-ray tube, the X-ray tube having a window for allowing X-rays to pass out of the tube,wherein the shutter in the blocking position is at a distance of not more than 20 mm from the window in the X-ray tube. 15. A shutter arrangement according to claim 10 wherein the housing is of brass. 16. A shutter arrangement according to claim 10 wherein the shutter consists essentially of tantalum. 17. A shutter arrangement according to claim 10 wherein the shutter is of an alloy containing tantalum, niobium or zirconium and another metal/element of atomic number above 26. 18. A shutter arrangement according to claim 10 further comprising an X-ray transparent window sealing the opening. 19. X-ray diffraction apparatus comprising:an X-ray tube having a window;a housing around the X-ray tube, the housing having an opening in the housing for allowing X-rays to pass through the opening from an inner face to an outer face of the X-ray housing, the X-ray housing being substantially opaque to X-rays; anda shutter movable between a blocking position adjacent to the opening where it blocks the opening and an open position where it allows X-rays to pass through the opening;a sample area for mounting a sample; andan X-ray detector for detecting X-rays emitted from the sample in the sample area;wherein the shutter is of tantalum, niobium or zirconium, or an alloy containing at least 80% of one of these elements and a further metal/element; andwherein the shutter is a block having a hole through the block, the hole being aligned with the opening when the shutter is in the open position to allow X-rays to pass through the opening and the shutter blocking the opening when the shutter is in the blocking position. 20. X-ray diffraction apparatus according to claim 19 wherein the hole through the block is sized to completely cover edges of the opening when the shutter is in the open position.