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An x-ray generating device includes a field emission cathode formed at least partially from a nanostructure-containing material having an emitted electron current density of at least 4 A/cm2. High energy conversion efficiency and compact design are achieved due to easy focusing of cold cathode emitt

An x-ray generating device includes a field emission cathode formed at least partially from a nanostructure-containing material having an emitted electron current density of at least 4 A/cm2. High energy conversion efficiency and compact design are achieved due to easy focusing of cold cathode emitted electrons and dramatic reduction of heating at the anode. In addition, by pulsing the field between the cathode and the gate or anode and focusing the electron beams at different anode materials, pulsed x-ray radiation with varying energy can be generated from a single device.

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1. An x-ray generating device comprising:a chamber; a field emission cathode, the cathode comprising a nanostructure-containing material having an emitted electron current density of more than 1 mA/cm2 when subjected to an applied electrical field of less than 3 V/μm; an anode target; and an acceler

1. An x-ray generating device comprising:a chamber; a field emission cathode, the cathode comprising a nanostructure-containing material having an emitted electron current density of more than 1 mA/cm2 when subjected to an applied electrical field of less than 3 V/μm; an anode target; and an accelerating field established by an applied potential between the cathode and anode. 2. The device of claim 1, wherein the nanostructure containing material has an emitted electron current density of more than 10 mA/cm2 when subjected to an applied electrical field of less than 4 V/μm.3. The device of claim 1, wherein the emitted current density is as great as 10 A/cm2.4. The device of claim 1, wherein an applied electrical field of greater than 2 V/μm produces a stable current density of at least about 100 mA/cm2.5. The device of claim 1, wherein an applied electrical field of 2-8 V/μm produces a stable current density of at least about 100 mA/cm2.6. The device of claim 1, wherein an applied electrical field less than 8 V/μm produces a stable current density greater than 100 mA/cm2.7. The device of claim 1, wherein the nanostructure-containing material comprises carbon nanotubes.8. The device of claim 1, wherein the nanostructure-containing material comprises single-walled carbon nanotubes.9. The device of claim 1, wherein the cathode comprises a substrate material at least partially covered with the nanostructure-containing material.10. The device of claim 9, further comprising a metal interlayer between the substrate and the nanostructure-containing material.11. The device of claim 9, further comprising a gate electrode which is electrically isolated from the cathode.12. The device of claim 9, wherein the nanostructure-containing material comprises a thin paper which is adhered to the substrate.13. The device of claim 11, wherein the nanostructure-containing material comprises a patterned film defined by electron emitting materials aligned with openings disposed in the gate electrode.14. The device of claim 11, further comprising a feedback circuit constructed to vary the applied electrical potential between the gate electrode and the cathode thereby improving stability of the generated x-rays.15. The device of claim 11, further comprising a focusing ring located above the gate electrode.16. The device of claim 1, comprising a gate electrode which is electrically isolated from the cathode,wherein the applied potential is between the cathode and gate electrode and is pulsed between on and off and produces a beam of field-emitted electrons during a period of the pulse being on and does not produce a beam of field-emitted electrons during a period of the pulse being off. 17. The device of claim 1, wherein the anode further comprises a plurality of target materials.18. The device of claim 17, wherein the device is capable of selectively producing x-rays of different energies.19. The device of claim 18, wherein a portion of the anode target comprises a first target material and another portion of the anode target comprises a second target material.20. The device of claim 19, wherein the anode target comprises a conical face.21. The device of claim 1, wherein the anode target comprises a focus spot 10-30 mm in length and 0.1-0.5 mm in width.22. The device of claim 1, wherein the anode target comprises a target angle of 2°-10°.23. The device of claim 1, wherein the device produces an apparent focal spot having an area of 0.1-0.5 mm2.24. The device of claim 1, wherein the anode target comprises a focus spot 10-30 mm in length and 0.1-0.5 mm in width, and a target angle of 2°-10°, the device producing an apparent focus spot having an area of 0.1-0.5 mm2.25. The device of claim 1, wherein the x-ray generating device is portable.26. A method for producing x-rays comprising:providing a chamber; introducing a field emission cathode into the chamber, the cathode comprising a nanostructure-containing material having an emitted electron current density of more than 1 mA/cm2 when subjected to an applied electrical field of less than 3 V/μm; applying a control voltage to the cathode thereby causing a stream of electrons to be emitted; and providing an anode target within the chamber incident to the stream of emitted electrons thereby causing x-rays to be emitted from the anode target. 27. The method of claim 26, wherein the nanostructure containing material has an emitted electron current density of more than 10 mA/cm2 when subjected to an applied electrical field of less than 4 V/μm.28. The method of claim 26, wherein the emitted current density is as great as 10 A/cm2.29. The method of claim 26, wherein the emitted electron current density is at least about 100 mA/cm2 when subjected to an applied electrical field of 2-7 V/μm.30. The method of claim 26, wherein an applied electrical field greater than 2 V/μm produces a stable current density of at least about 100 mA/cm2.31. The method of claim 26, wherein an applied electrical field of 2-8 V/μm produces a stable current density of at least about 100 mA/cm2.32. The method of claim 26, wherein an applied electrical field less than 8 V/μm produces a stable current density greater than 100 mA/cm2.33. The method of claim 29, wherein the emitted electron current density is stable.34. The method of claim 26, further comprising pulsing the incident electron beam.35. The method of claim 34, wherein the pulsing of the incident beam is caused by the application and removal of the electric field on the field emission cathode.36. The method of claim 26, wherein the nanostructure containing material comprises single walled carbon nanotubes.37. The method of claim 36, wherein the cathode comprises a substrate at least partially covered with the nanostructure-containing material.38. The method of claim 26, further comprising providing the anode target with a portion comprising a first target material and with another portion comprising a second target material, and causing a first stream of electrons to strike the first target material and a second stream of electrons to strike the second target material, thereby causing the device to generate x-rays of different energies by applying the same control voltage.39. The method of claim 26, further comprising processing the anode target with a focus spot 10-30 mm in length, 0.1-0.5 mm in width, and a target angle of 2°-10° thereby producing an apparent focus spot having an area of 0.1-0.5 mm2.40. The method of claim 26, wherein the amount of applied voltage is utilized to generate an x-ray beam of predetermined density and distribution.41. An x-ray generating device comprising:a chamber; a field emission cathode, the cathode comprising a nanostructure-containing electron emissive material; an anode target; and an accelerating field established by an applied electrical potential between the cathode and anode, wherein the nanostructure-containing material has an emitted electron current density of more than 1 mA/cm2 when subjected to an applied electrical field of less than 3 V/μm. 42. The device of claim 41, wherein the emitted current density is as great as 10 A/cm2.43. The device of claim 41, wherein an applied electrical field of greater than 2 V/μm produces a stable current density of at least about 100 mA/cm2.44. The device of claim 41, wherein the x-ray generating device is portable.45. An x-ray generating device comprising:a chamber; a field emission cathode, the cathode comprising a nanostructure-containing electron emissive material; an anode target; and an accelerating field established by an applied electrical potential between the cathode and anode, wherein the nanostructure containing material has an emitted electron current density of more than 10 mA/cm2 when subjected to an applied electrical field of less than 5 V/μm. 46. The device of claim 45, wherein the emitted current density is as great as 10 A/cm2.47. The device of claim 45, wherein an applied electrical field of 2-8 V/μm produces a stable current density of at least about 100 mA/cm2.48. The device of claim 45, wherein the x-ray generating device is portable.49. An x-ray generating device comprising:a chamber; a field emission cathode, the cathode comprising a nanostructure-containing electron emissive material; an anode target; and an accelerating field established by an applied electrical potential between the cathode and anode, wherein an applied electrical field less than 8 V/μm produces a stable current density greater than 100 mA/cm2. 50. The device of claim 49, wherein the x-ray generating device is portable.51. A method for producing x-rays comprising:providing a chamber; introducing a field emission cathode into the chamber, the cathode comprising a nanostructure-containing electron emissive material; applying a control voltage to the cathode thereby causing a stream of electrons to be emitted; and providing an anode target within the chamber incident to the stream of emitted electrons thereby causing x-rays to be emitted from the anode target, wherein the nanostructure-containing material has an emitted electron current density of more than 10 mA/cm2 when subjected to an applied electrical field of less than 4 V/μm. 52. A The method for producing x-rays comprising:providing a chamber; introducing a field emission cathode into the chamber, the cathode comprising a nanostructure-containing electron emissive material; applying a control voltage to the cathode thereby causing a stream of electrons to be emitted; and providing an anode target within the chamber incident to the stream of emitted electrons thereby causing x-rays to be emitted from the anode target, wherein the nanostructure-containing material has an emitted current density of as great as 10 A/cm2. 53. A method for producing x-rays comprising:providing a chamber; introducing a field emission cathode into the chamber, the cathode comprising a nanostructure-containing electron emissive material; applying a control voltage to the cathode thereby causing a stream of electrons to be emitted; and providing an anode target within the chamber incident to the stream of emitted electrons thereby causing x-rays to be emitted from the anode target, wherein the nanostructure-containing material has an emitted current density of at least about 100 mA/cm2 when subjected to an applied electrical field of 2-8 V/μm. 54. A method for producing x-rays comprising:providing a chamber; introducing a field emission cathode into the chamber, the cathode comprising a nanostructure-containing electron emissive material; applying a control voltage to the cathode thereby causing a stream of electrons to be emitted; and providing an anode target within the chamber incident to the stream of emitted electrons thereby causing x-rays to be emitted from the anode target, wherein the nanostructure-containing material has an emitted current density greater than 100 mA/cm2 when subjected to an applied electrical field of less than 8 V/μm.