Method and apparatus for extending angular coverage for a scanning two-dimensional X-ray detector
View Patent ↗A method and apparatus for performing an X-ray diffraction measurement with a diffractometer having an X-ray beam directed at a sample and a two-dimensional X-ray detector includes the performance of a physical scan during which the detector is moved through a scanning range in an angular direction about the sample position. To provide a uniform exposure time, the detector, when located at an extreme of the scanning range, is controlled to progressively change the portion of the detected X-ray energy that is used at a rate that maintains a uniform exposure time for each angular position in the scanning range. Alternatively, when located at an extreme of the range, the detector is kept stationary until a desired minimum exposure time is obtained for each angular position, after which the collected diffraction data is normalized relative to exposure time.
1. A method for performing an X-ray diffraction measurement with an X-ray diffractometer that has an X-ray beam directed at a sample, that detects X-ray energy diffracted by the sample with a two-dimensional X-ray detector and that stores a representation of the detected X-ray energy as a spatial intensity distribution relative to a detection area comprising a cylindrical segment, the method comprising:
moving the detector in an angular direction along a scanning path about a location of the sample while detecting the diffracted X-ray energy; and
when the detector is located at an extreme of the scanning path, maintaining the position of the detector while detecting the X-ray energy, and progressively changing, along said angular direction, a portion of the X-ray energy being detected that is used to contribute to said representation of the detected X-ray energy.
2. A method according to claim 1 wherein the extreme of the scanning path is the beginning of the scanning path, and wherein progressively changing a portion of the X-ray energy being detected that is used to contribute to said representation comprises progressively increasing said portion before moving the detector along the scanning path.
3. A method according to claim 1 wherein the extreme of the scanning path is the end of the scanning path, and wherein progressively changing a portion of the X-ray energy being detected that is used to contribute to said representation comprises progressively decreasing said portion after moving the detector along the scanning path.
4. A method according to claim 1 wherein the detector is moved such that an angular range of said detection area for which detected X-ray energy is used to contribute to said representation changes at a predetermined speed, and wherein progressively changing a portion of the X-ray energy being detected that is used to contribute to said representation comprises changing said portion at a rate that matches said predetermined speed.
5. A method according to claim 1 wherein a spatial distribution of X-ray energy detected by the detector is transformed with a cylindrical projection prior to being used to contribute to said representation of the detected X-ray energy.
6. A method according to claim 5 wherein progressively changing a portion of the X-ray energy being detected that is used to contribute to said representation comprises progressively changing said portion along said angular direction after the detected X-ray energy is transformed with said cylindrical projection.
7. A method according to claim 1 wherein the detector moves along the scanning path with a stepwise motion.
8. A method according to claim 1 wherein the detector moves along the scanning path with a continuous motion.
9. A method according to claim 1 wherein the detector comprises a two-dimensional array of pixels.
10. A method according to claim 9 wherein changing a portion of the X-ray energy being detected that is used to contribute to said representation comprises changing the pixels from which detected X-ray energy is used for contributing to said representation.
11. A method according to claim 10 wherein pixel columns in the detector are perpendicular to the scanning path, and wherein changing the pixels from which detected X-ray energy is used comprises changing the pixels column-by-column in a direction perpendicular to the pixel columns.
12. A method according to claim 9 wherein a spatial distribution of X-ray intensities detected by the pixels in the plane of the detector is stored as a spatial distribution of X-ray intensities in a cylindrical projection of the detector pixels that substantially corresponds to the detection area.
13. A method according to claim 12 wherein changing the portion of the X-ray energy being detected that is used to contribute to said representation comprises changing the pixels, as projected in the cylindrical projection, from which said X-ray intensities are used column-by-column along a direction of the scanning path.
14. An X-ray diffractometer for performing an X-ray diffraction measurement of a sample comprising:
an X-ray beam directed at the sample;
a two-dimensional X-ray detector that detects X-ray energy diffracted by the sample; and
a scanning system that moves the detector in an angular direction along a scanning path about a location of the sample while detecting the diffracted X-ray energy and stores a representation of the detected X-ray energy as a spatial intensity distribution relative to a detection area comprising a cylindrical segment wherein, when the detector is located at an extreme of the scanning path, the position of the detector is maintained while detecting the X-ray energy, and a portion of the X-ray energy being detected that is used to contribute to said representation of the detected X-ray energy is progressively changed along said angular direction.
15. A diffractometer according to claim 14 wherein the extreme of the scanning path is the beginning of the scanning path, and wherein the portion of the X-ray energy being detected that is used to contribute to said representation is progressively increased before moving the detector along the scanning path.
16. A diffractometer according to claim 14 wherein the extreme of the scanning path is the end of the scanning path, and wherein the portion of the X-ray energy being detected that is used to contribute to said representation is progressively decreased after moving the detector along the scanning path.
17. A diffractometer according to claim 14 wherein the detector is moved such that an angular range of said detection area for which detected X-ray energy is used to contribute to said representation changes at a predetermined speed, and wherein progressively changing a portion of the X-ray energy being detected that is used to contribute to said representation comprises changing said portion at a rate that matches said predetermined speed.
18. A diffractometer according to claim 14 wherein the scanning system transforms a spatial distribution of X-ray energy detected by the detector with a cylindrical projection prior to it being used to contribute to said representation of the detected X-ray energy.
19. A diffractometer according to claim 18 wherein the portion of the X-ray energy being detected that is used to contribute to said representation of the detected X-ray energy is progressively changed along said angular direction after the detected X-ray energy is transformed with said cylindrical projection.
20. A diffractometer according to claim 14 wherein the scanning system moves the detector along the scanning path with a stepwise motion.
21. A diffractometer according to claim 14 wherein the scanning system moves the detector along the scanning path with a continuous motion.
22. A diffractometer according to claim 14 wherein the detector comprises a two-dimensional array of pixels.
23. A diffractometer according to claim 22 wherein the portion of the X-ray energy being detected that is used to contribute to said representation is changed by changing the pixels from which detected X-ray energy is used for contributing to said representation.
24. A diffractometer according to claim 23 wherein pixel columns in the detector are perpendicular to the scanning path, and wherein the pixels from which detected X-ray energy is used are changed column-by-column in a direction perpendicular to the pixel columns.
25. A diffractometer according to claim 22 wherein a spatial distribution of X-ray intensities detected by the pixels in the plane of the detector is stored as a spatial distribution of X-ray intensities in a cylindrical projection of the detector pixels that substantially corresponds to the detection area.
26. A diffractometer according to claim 25 wherein changing the portion of the X-ray energy being detected that is used to contribute to said representation comprises changing the pixels, as projected in the cylindrical projection, from which said X-ray intensities are used column-by-column along a direction of the scanning path.
27. A method for performing an X-ray diffraction measurement with an X-ray diffractometer having an X-ray beam directed at a sample and a two-dimensional X-ray detector that collects X-ray energy diffracted by the sample, the method comprising:
performing a scan by collecting said diffracted X-ray energy while moving the detector through a scanning range in an angular direction about a location of the sample at a speed of Δα/Δt, where Δα is an angular distance that corresponds to the distance between adjacent columns of detector pixels perpendicular to the scan direction;
when the detector is located at an extreme of the scanning range, maintaining the position of the detector and actively collecting said diffracted X-ray energy for a duration of N(Δt), where N is the number of said pixel columns; and
normalizing a measured intensity of the diffracted X-ray energy collected by the detector relative to exposure time.
28. A method according to claim 27 wherein said extreme of the scanning range is the beginning of the scanning range.
29. A method according to claim 27 wherein said extreme of the scanning range is the end of the scanning range.
30. A method according to claim 27 wherein, when the detector is moving, an exposure time for the detector is substantially the same for any angular position along the scanning range.
31. A method according to claim 27 wherein the detector moves through the scanning range with a stepwise motion.
32. A method according to claim 27 wherein the detector moves through the scanning range with a continuous motion.