Diffractometer
A compact powder diffractometer has one or more detectors arranged no more than 300 mm, in an example 55 mm, from a sample stage for mounting a powder sample. High resolution is nevertheless obtained in spite of the small dimensions using a geometry that achieves a suitable divergence of X-rays incident on the sample and a small spot size using a grazing exit condition on a monochromator crystal.
1. A powder diffractometer for measuring a powder sample, comprising:
a sample stage for holding the powder sample;
an X-ray source for emitting an X-ray beam;
a monochromator crystal having a diffraction surface arranged to diffract a monochromatic X-ray beam at a grazing exit angle of less than 5° to the diffraction surface towards the sample stage to have a spot width of less than 60 μm at the sample stage;
at least one detector crystal for measuring intensities of X-rays passing through the sample having been diffracted from the powder sample simultaneously at a plurality of diffraction angles; and
processing means for calculating a diffraction pattern from the measured X-rays.
2. A diffractometer according to claim 1 wherein each detector crystal is arranged 300 mm or less from the sample stage.
3. A diffractometer according to claim 1 wherein each detector crystal is arranged 100 mm or less from the sample stage.
4. A diffractometer according to claim 1 wherein the monochromatic crystal is arranged to diffract the monochromatic X-ray beam incident on the sample with an angular divergence from 0.005° to 0.02°.
5. A diffractometer according to claim 1 further comprising a parabolic mirror arranged to direct the X-ray beam from the X-ray source towards the monochromator crystal.
6. A diffractometer according to claim 1 , wherein each detector crystal is planar.
7. A diffractometer according to claim 1 , wherein the sample stage has a mounting surface of adhesive material for adhering a thin layer of powder sample.
8. A diffractometer according to claim 1 comprising a plurality of detector crystals,
wherein the detector crystals are arranged on alternating sides of a line passing through the sample stage along the line of the monochromatic X-ray beam from the monochromator.
9. A diffractometer according to claim 1 , further comprising:
means for moving the sample stage perpendicularly to the X-ray beam at the sample stage during data collection;
wherein the processing means are adapted to process the measured X-ray intensities whilst measurements are being made and to stop data collection when sufficient data has been collected.
10. A method of making diffraction measurements, comprising:
mounting a powder sample on a sample stage;
emitting an X-ray beam from an X-ray source onto a monochromator crystal having a diffraction surface arranged to diffract a monochromatic X-ray beam at a grazing exit angle of less than 5° to the diffraction surface towards the sample stage to have a spot width of less than 60 μm at the sample stage;
measuring intensities of X-rays passing through and diffracted from the powder sample simultaneously at a plurality of diffraction angles using at least one detector crystal; and
calculating a diffraction pattern from the measured X-rays.
11. A method according to claim 10 , wherein the detector is arranged 300 mm or less from the sample stage.
12. A method according to claim 10 wherein the monochromatic crystal is arranged to diffract the monochromatic X-ray beam incident on the sample to have an angular divergence from 0.005° to 0.02°.
13. A method according to claim 10 wherein the powder sample has a thickness no greater than 10 μm.
14. A method according to claim 10 including mounting the powder sample on a mounting surface of adhesive material on the sample stage.
15. A method according to claim 10 further comprising measuring the intensities using a plurality of detector crystals arranged on alternating sides of a line passing through the sample along the line of the monochromatic X-ray beam from the monochromator to the sample.
16. The method according to claim 10 further comprising moving the sample stage during data collection.
17. The method according to claim 10 further comprising processing the measured X-ray intensities whilst measurements are being made and stopping the data collection when sufficient data has been collected.