Patent Number: 
Section: claims

1. A collimation device for an X-ray beam, comprising:an enclosure configured to be placed under vacuum or controlled atmosphere, the enclosure comprising an entrance and an exit for the X-ray beam, and at least one first plate made of a material with a diffracting periodic structure,the first plate comprising first and second principal faces and at least one first aperture broadening out between the first and second principal faces,wherein at least one of the first and second plates is made of a monocrystalline material. 2. The device as claimed in claim 1, in which the first principal face of the at least one first plate is an upstream face, with reference to a direction of propagation of the X-ray beam, and the second principal face is a downstream face, the first aperture widens out from the upstream face to the downstream face of the first plate. 3. The device as claimed in claim 1, in which the at least one first plate made of material with a diffracting periodic structure is arranged at a level of the exit of the enclosure. 4. The device as claimed in claim 3, further comprising, at a level of the entrance of the enclosure, at least one second plate made of a material with a diffracting periodic structure, the second plate comprising third and fourth principal faces and at least one second aperture broadening out between the third and fourth faces. 5. The device as claimed in claim 4, in which the third principal face of the at least one second plate is an upstream face, with reference to the direction of propagation of the beam, and the fourth principal face is a downstream face, and the second aperture widens out from the upstream face to the downstream face of the at least one second plate. 6. The device as claimed in claim 4, in which the first and second plates are identical. 7. The device as claimed in claim 4, in which the first and second plates exhibit different apertures. 8. The device as claimed in claim 1, in which an acute angle θ formed between a direction of broadening out of one of the apertures and one of the principal faces is between 10° and 80°. 9. The device as claimed in claim 8, in which the angle θ is equal to the angle between two crystalline planes of the monocrystalline material of diffracting periodic structure forming the first plate. 10. The device as claimed in the preceding claim, in which:the principal faces of the plates correspond to the {100} plane of the monocrystalline material; andthe faces of the apertures connecting the principal faces of this plate correspond to the {111} plane. 11. The device as claimed in claim 1, in which at least one of the first and second plates is made of a material chosen from among silicon or germanium. 12. An optical device for analyzing a specimen by scattering of an X-ray beam, comprising a device for collimating the beam as claimed in claim 1. 13. The optical device as claimed in claim 12, further comprising an X-ray source. 14. The optical device as claimed in claim 13, in which the X-ray source produces a monochromatic beam. 15. The optical device as claimed in claim 12, further comprising another enclosure configured to be placed under vacuum or controlled atmosphere, the other enclosure, arranged downstream of the specimen, comprising a means for stopping the X-ray beam. 16. The optical device as claimed in claim 15, further comprising a detector, arranged downstream of the other enclosure. 17. A collimator for an X-ray beam, comprising:plural parts, of an X-ray aperture;each part made of a monocrystalline material with a diffracting periodic structure, and comprising at least one aperture broadening out in the thickness thereof;faces of the X-ray aperture, formed by assembling said plural parts, forming a sawtooth structure along a longitudinal axis of the X-ray aperture. 18. The collimator as claimed in claim 17, in which each of the parts is formed of a plate, the plates being adjoining. 19. The collimator as claimed in claim 18, in which the plates are identical. 20. A method for using a collimator for an X-ray beam, comprising:illumination a specimen with X-rays;wherein the collimator comprise at least one plate made of a monocrystalline material with a diffracting periodic structure, the plate comprising two principal faces and at least one aperture broadening out between the faces. 21. The method of claim 20, in which an acute angle θ formed between a direction of broadening out of the aperture and one of the principal faces is between 10° and 80°. 22. The method of claim 20, in which the collimator comprises plural identical plates adjoining one another.