Patent Number: 
Section: claims

1. A scanning apparatus for scanning a beam in a single dimensional scan, the apparatus comprising:a. a source of radiation for generating a fan beam of radiation effectively emanating from a source axis and characterized by a width;b. an angle selector, stationary during the course of scanning, for limiting the angular extent of the scan; andc. a multi-aperture unit rotatable about a central axis in such a manner that beam fluence incident on a target is the same per revolution for different fields of view of the beam on the target. 2. A scanning apparatus in accordance with claim 1, wherein the multi-aperture unit includes rings of apertures spaced laterally along the central axis in such a manner that relative axial motion of the multi-aperture unit, relative to the x-ray beam plane, places a ring of apertures in the beam that is collimated by a corresponding opening angle in the angle selector. 3. A scanning apparatus in accordance with claim 1, wherein the angle selector includes a slot of continuously variable opening. 4. A scanning apparatus in accordance with claim 1, wherein the central axis is substantially coincident with the source axis. 5. A scanning apparatus in accordance with claim 1, wherein the multi-aperture unit includes rectangular slots. 6. A scanning apparatus in accordance with claim 1, wherein the source axis is forward-offset relative to the central axis. 7. A scanning apparatus in accordance with claim 1, further comprising a collimator for limiting at least one of a width of the beam and an angular extent of the scan. 8. A scanning apparatus in accordance with claim 7, wherein the collimator is a width collimator. 9. A scanning apparatus in accordance with claim 8, wherein the collimator is an inner collimator. 10. A scanning apparatus in accordance with claim 8, wherein the collimator is an outer collimator. 11. A scanning apparatus in accordance with claim 1, wherein the angle selector includes a plurality of discrete slots. 12. A scanning apparatus in accordance with claim 10, wherein the angle selector includes a shutter position. 13. A scanning apparatus in accordance with claim 1, wherein the source of radiation is an x-ray tube. 14. A scanning apparatus in accordance with claim 1, wherein the source of radiation is of a type generating a fan beam exceeding 60° in opening angle. 15. A scanning apparatus in accordance with claim 1, further comprising an enclosing conveyance for conveying the scanning apparatus past an inspection target. 16. A scanning apparatus in accordance with claim 1, wherein the scanning apparatus is coupled to a platform. 17. A scanning apparatus in accordance with claim 1, wherein the scanning apparatus is coupled to a platform in conjunction with at least one further scanning apparatus. 18. A scanning apparatus in accordance with claim 1, further comprising a filter disposed within the beam for changing the energy distribution of the beam. 19. A scanning apparatus in accordance with claim 18, wherein the filter is disposed on a filter tube adapted for selective insertion of a plurality of filters. 20. A scanning apparatus in accordance with claim 18, wherein the filter tube includes a beam shutter. 21. A scanning apparatus in accordance with claim 1, wherein the multi-aperture unit includes two nested, multi-aperture collimators. 22. A scanning apparatus in accordance with claim 1, wherein the multi-aperture unit includes an inner multi-aperture hoop characterized by a hoop axis, the inner multi-aperture hoop made of material opaque to the beam. 23. A scanning apparatus in accordance with claim 21, wherein the inner multi-aperture unit includes rings of apertures spaced laterally along the hoop axis in such a manner that relative axial motion of the inner multi-aperture unit, relative to the beam plane, places a ring of apertures in the beam that is collimated by a corresponding opening angle in the angle selector. 24. A scanning apparatus in accordance with claim 1, wherein the multi-aperture unit includes an outer multi-aperture hoop rotatable in registration with an inner multi-aperture hoop. 25. A scanning apparatus in accordance with claim 23, wherein the outer multi-aperture hoop includes a plurality of apertures configured as horizontal slots in such a manner as to define a minimum size of emitted pencil beams along a sweep direction of the beams. 26. A scanning apparatus in accordance with claim 23, wherein the inner multi-aperture hoop and the outer multi-aperture hoop are mechanically integral. 27. A scanning apparatus in accordance with claim 23, further comprising an outer variable width collimator for defining a width of the beam that enters or exits the outer multi-aperture hoop. 28. A scanning apparatus in accordance with claim 1, wherein radiation is emitted through a plurality of apertures at different angles with respect to the target, such that pencil beams of penetrating radiation sweep in alternation through the target in such a manner as to provide a stereoscopic view of an interior volume of the target. 29. A scanning apparatus in accordance with claim 1, further comprising a rotation assembly adapted to provide for rotation of the source of radiation about the source axis. 30. A scanning apparatus in accordance with claim 1, wherein the multi-aperture unit includes substantially rectangular through-holes. 31. A method for inspecting an object based on the transmission of x-rays through an object, the method comprising:a. generating a fan beam of radiation;b. collimating the width of the fan beam with a collimator that is stationary during the course of a scan of the object, the scan characterized by an extent;c. limiting the extent of the scan with an angle selector; andd. varying a field of view of the beam on the object by means of a multi-aperture unit rotatable about a central axis in such a manner that the resulting beam fluence on the target is the same per revolution for all selected scan angles.