Patent Number: 059404698
Section: claims

1. An x-ray source for generating multi-chromatic x-rays comprising: a cathode which emits an electron beam;  an anode disposed in a path of said electron beam and emitting x-ray bremsstrahlung upon being struck by said electron beam;  a target on which said x-ray bremsstrahlung is incident which converts the x-ray bremsstrahlung incident thereon into fluorescence radiation, said target being composed of a plurality of sections with each section being comprised of a different material, and said cathode surrounding said target; and  means for selectively irradiating one of said sections of said target at a time with said x-ray bremsstrahlung.  a cathode comprised of two cathode sections, each capable of emitting, when driven, an electron beam, the respective electron beams emitting by said cathode sections proceeding along respective beam paths;  means for separately driving said two cathode sections for causing only one of said cathode sections to emit an electron beam at a time;  an anode composed of two anode sections disposed opposite each other, said anode sections being respectively disposed in said respective beam paths so that each anode section is struck by only one of said electrode beams respectively emitted by said cathode sections, each of said cathode sections, when struck by the respective electron beam, emitting x-ray bremsstrahlung; and  a needle-shaped target having a longitudinal middle plane dividing said target into two target sections, the bremsstrahlung emitted by the respective anode sections being respectively incident on said target sections, each of said target sections being comprised of a different material and converting the bremsstrahlung respectively incident thereon into fluorescence radiation.  a cathode at a cathode potential which emits an electron beam;  an anode disposed in a path of said electron beam and emitting x-ray bremsstrahlung upon being struck by said electron beam;  a target on which said x-ray bremsstrahlung is incident which converts the x-ray bremsstrahlung incident thereon into fluorescence radiation, said target being composed of a plurality of sections with each section being comprised of a different material;  means for placing said target at said cathode potential; and  means for selectively irradiating one of said sections at a time with said x-ray bremsstrahlung. 2. An x-ray source as claimed in claim 1 further comprising a base plate having a radiation exit window therein disposed opposite said target through which said fluorescence radiation passes. 3. An x-ray source for generating multi-chromatic x-rays comprising: 4. An x-ray source as claimed in claim 3 wherein said anode comprises an anode ring having an anode ring axis and wherein said longitudinal middle plane of said needle-shaped target is disposed perpendicular to said ring axis, said anode ring having a wedge ring projecting toward said anode ring axis and being symmetrical relative to said longitudinal middle plane of said wedge ring having an upper surface forming a first of said two anode sections and a lower surface forming a second of said two anode sections target, and wherein said two sections of said cathode respectively comprise a firs cathode ring, disposed above said middle plane of said target, and first focusing means for focusing an electron beam emitted by said first ring cathode only onto said upper surface of said wedge ring, and a second ring cathode, disposed below said longitudinal middle plane of said target, and second focusing means for focusing an electron beam emitted by said second ring electrode onto said lower surface of said wedge ring. 5. An x-ray source as claimed in claim 4 wherein said wedge ring has a hollow interior, and said x-ray source further comprising a liquid guide surface projecting into said hollow interior of said wedge ring and forming a coolant channel in said wedge ring. 6. An x-ray source as claimed in claim 5 wherein said guide surface has a wedge-shape. 7. An x-ray source as claimed in claim 4 wherein said wedge ring has a heel angle associated therewith, and wherein said upper and lower surfaces of said wedge ring are disposed relative to each other at a wedge angle which is less than or equal to twice said heel angle. 8. An x-ray source as claimed in claim 7 wherein said cathode comprises upper and lower ring cathodes respectively disposed above and below said target, and first and second sets of focusing coils respectively oriented relative to said first and second ring cathodes for focusing respective electron beams emitted thereby, and wherein said x-ray source further comprises a carrying tube for said lower ring cathode, said carrying tube projecting toward said target from said base plate, and said focusing coils for said lower ring cathode being mounted on said carrying tube and said x-ray exit window being disposed in said carrying tube. 9. An x-ray source for generating multi-chromatic x-rays comprising: