Patent Number: 050383701
Section: claims

1. Apparatus for generating an X-ray or gamma beam with small cross-section and variable direction comprising an X-ray or gamma emitter, from the focus of which a bundle of rays emerges, and a diaphragm arrangement, which cuts out a beam from the bundle of rays and comprises a hollow-cylindrical first diaphragm body which is rotatable about its axis of symmetry and has two mutually offset helical slits on the circumference, said slits winding around the diaphragm body in at least one turn each and are shaped in such a way that at least one straight line runs through the slits towards the focus, the position of which line can be varied by rotation of the diaphragm body. 2. Apparatus according to claim 1 wherein each slit has an integral number of turns. 3. Apparatus according to claim 1 including a second diaphragm body which only allows there through a primary beam of the bundle of rays, and in that the second diaphragm body is arranged such that the primary beam always coincides with said at least one straight line. 4. Apparatus according to claim 3 wherein the second diaphragm body has the form of a hollow cylinder, the axis of which lies in the plane containing the axis of symmetry and the focus and the cross-section of which is circular and in that the second diaphragm body is provided with two helical slits mutually offset by 180.degree. on the circumference. 5. Apparatus according to claim 4, wherein the slits on the circumference of the second diaphragm body describe in angle of 180.degree.. 6. Apparatus according to claim 5 including a drive device which drives the first diaphragm body at 2n times the angular velocity as the second diaphragm body. 7. Apparatus according to claim 6 wherein the angle at the circumference which a slit on the first diaphragm body describes is greater by a factor of 2n than the angle at circumference described by a slit on the second diaphragm body where n is an integer. 8. Apparatus according to claim 4 wherein the two diaphragm bodies are arranged concentrically to each other and one encloses the other and in that the slits of the second diaphragm body are wider than at least one of the slits in the first diaphragm body. 9. Apparatus according to claim 8 wherein the first diaphragm body encloses the second diaphragm body. 10. Apparatus according to claim 1 wherein the slits of the diaphragm body have pitches differing from each other. 11. Apparatus according to claim 10 wherein of the slits in the diaphragm body, the one with the greater pitch is narrower than the other one. 12. Apparatus according to claim 1 including a slit diaphragm, the slit of which coincides with the axis of rotation of the diaphragm body and which determines the dimensions of the cut-out beam in the direction perpendicular to its longitudinal direction. 13. Apparatus according to claim 3 wherein the second diaphragm body has the form of a hollow cylinder, the axis of which lies in the plane containing the axis of symmetry and the focus and the cross-section of which is semicircular and in that the second diaphragm body is provided with one slit of semicircular cross-section. 14. Apparatus according to claim 13 wherein the slit on the circumference of the second diaphragm body describes an angle of 180.degree.. 15. Apparatus according to claim 2 including a second diaphragm body which only allows there through a primary beam of the bundle of the rays, and in that the second diaphragm body is arranged such that the primary beam always coincides with said at least one straight line. 16. Apparatus according to claim 13 wherein the two diaphragm bodies are arranged concentrically to each other an one encloses the other and in that the slit of the second diaphragm body is wider than at least one of the slits in the first diaphragm body. 17. Apparatus according to claim 16 wherein the first diaphragm body encloses the second diaphragm body. 18. Apparatus according to claim 17 wherein the slits of the first mentioned diaphragm body have pitches differing from each other. 19. Apparatus according to claim 18 wherein of the slits in the first diaphragm body, the one with the greater pitch is narrower than the other one. 20. Apparatus according to claim 19 including a slit diaphragm the slit of which coincides with the axis of rotation of the first diaphragm body and which determines the dimensions of the cut-out beam in the direction perpendicular to its longitudinal direction.