Patent Number: 061852791
Section: claims

1. Casing for electromagnetic radiation source, comprising a window made of a material which is transparent to the radiation emitted by the source, wherein that the window comprises at least one chamber in which a material that is opaque to electromagnetic radiation can move, this chamber being designed in such a way that the material that is opaque to radiation can be introduced from the exterior of the chamber and that, inside the chamber, this material that is opaque to radiation surrounds a region for passage of a radiation beam in such a way that the area of the beam passage region varies as a function of the volume of opaque material in the chamber, by virtue of which parasitic extrafocal radiation is eliminated from the beam. 2. Casing according to claim 1 wherein that the chamber comprises a first channel wound on itself in the shape of a spiral. 3. Casing according to claim 2 wherein the chamber comprises a second channel in the shape of a spiral, juxtaposed with the first channel in a direction perpendicular to the planes on which the openings of the first and second channels are located, this first and this second channel being offset relative to each other in such a way that the turns of one spiral cover the space between the turns of the other spiral, so as to ensure complete opacity to radiation in the part of the spirals through which the opaque material passes. 4. Casing according to claim 1 wherein a part of the volume of the chamber is occupied by the material that is opaque to radiation and the remaining volume is occupied by a fluid that is transparent to radiation. 5. Casing according to claim 2 wherein a part of the volume of the chamber is occupied by the material that is opaque to radiation and the remaining volume is occupied by a fluid that is transparent to radiation. 6. Casing according to claim 3 wherein a part of the volume of the chamber is occupied by the material that is opaque to radiation and the remaining volume is occupied by a fluid that is transparent to radiation. 7. Casing according to claim 4 wherein the material that is opaque to radiation is contained at the periphery of the chamber and the fluid that is transparent to radiation is contained at its center. 8. Casing according to claim 5 wherein the material that is opaque to radiation is contained at the periphery of the chamber and the fluid that is transparent to radiation is contained at its center. 9. Casing according to claim 6 wherein the material that is opaque to radiation is contained at the periphery of the chamber and the fluid that is transparent to radiation is contained at its center. 10. Casing according to claim 1 wherein the material that is opaque to radiation is liquid mercury. 11. Casing according to claim 4 wherein the fluid that is transparent to radiation is alcohol. 12. Casing according to claim 11 wherein the fluid that is transparent to radiation is alcohol. 13. Casing according to claim 1 wherein the window has the shape of a frustoconical dome having an end wall and a sidewall, the chamber comprising at least one channel wound in a spiral, arranged in the end wall, and an annular cavity, arranged in the sidewall and communicating with the spiral channel(s). 14. Casing according to claim 2 wherein the window has the shape of a frustoconical dome having an end wall and a sidewall, the chamber comprising at least one channel wound in a spiral, arranged in the end wall, and an annular cavity, arranged in the sidewall and communicating with the spiral channel(s). 15. Casing according to claim 3 wherein the window has the shape of a frustoconical dome having an end wall and a sidewall, the chamber comprising at least one channel wound in a spiral, arranged in the end wall, and an annular cavity, arranged in the sidewall and communicating with the spiral channel(s). 16. Casing according to claim 4 wherein the window has the shape of a frustoconical dome having an end wall and a sidewall, the chamber comprising at least one channel wound in a spiral, arranged in the end wall, and an annular cavity, arranged in the sidewall and communicating with the spiral channel(s). 17. Casing according to claim 5 wherein the window has the shape of a frustoconical dome having an end wall and a sidewall, the chamber comprising at least one channel wound in a spiral, arranged in the end wall, and an annular cavity, arranged in the sidewall and communicating with the spiral channel(s). 18. Casing according to claim 6 wherein the window has the shape of a frustoconical dome having an end wall and a sidewall, the chamber comprising at least one channel wound in a spiral, arranged in the end wall, and an annular cavity, arranged in the sidewall and communicating with the spiral channel(s). 19. Casing according to claim 7 wherein the window has the shape of a frustoconical dome having an end wall and a sidewall, the chamber comprising at least one channel wound in a spiral, arranged in the end wall, and an annular cavity, arranged in the sidewall and communicating with the spiral channel(s). 20. Casing according to claim 10 wherein the window has the shape of a frustoconical dome having an end wall and a sidewall, the chamber comprising at least one channel wound in a spiral, arranged in the end wall, and an annular cavity, arranged in the sidewall and communicating with the spiral channel(s). 21. Casing according to claim 11 wherein the window has the shape of a frustoconical dome having an end wall and a sidewall, the chamber comprising at least one channel wound in a spiral, arranged in the end wall, and an annular cavity, arranged in the sidewall and communicating with the spiral channel(s). 22. Casing according to claim 1 wherein the electromagnetic radiation source is an X-ray source. 23. Method for eliminating the extrafocal radiation from a beam of electromagnetic radiation emitted by a source, comprising the steps of providing a casing of the electromagnetic radiation source with a window having a chamber and introducing into the chamber the desired quantity of radiation-opaque material to absorb the extrafocal radiation.