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A flash radiography diode includes a cathode and an anode. The cathode includes a frustum member with a bore extending through the frustum member. The anode is a tapered anode made of an electrically conductive material and oriented toward the cathode. The anode and the cathode are housed in a chamb

A flash radiography diode includes a cathode and an anode. The cathode includes a frustum member with a bore extending through the frustum member. The anode is a tapered anode made of an electrically conductive material and oriented toward the cathode. The anode and the cathode are housed in a chamber with a gap between the anode and the cathode. The cathode is configured to emit electrons to the tapered anode, which electrons strike the anode and create an anode plasma. The anode plasma creates X rays which propagate from the anode.

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What is claimed is: 1. A flash radiography diode, comprising: a cathode comprising a frustum member with a bore extending through the frustum member; a tapered anode comprising an electrically conductive material, the cathode and the tapered anode housed in a chamber, wherein the cathode is configu

What is claimed is: 1. A flash radiography diode, comprising: a cathode comprising a frustum member with a bore extending through the frustum member; a tapered anode comprising an electrically conductive material, the cathode and the tapered anode housed in a chamber, wherein the cathode is configured to emit an electrical pulse to the tapered anode; a gap between the tapered anode and the frustum member; and wherein the frustum member further comprises a flange having an outwardly flared wall at a first end proximate to the anode. 2. The flash radiography diode of claim 1, wherein the cathode comprises carbon. 3. The flash radiography diode of claim 1, wherein the tapered anode comprises at least one material selected from the group consisting of brass, copper, tungsten, tungsten alloy, stainless steel, lead and tantalum. 4. The flash radiography diode of claim 1, wherein a taper of the tapered anode is 20 degrees. 5. The flash radiography diode of claim 1, wherein the frustum member comprises a cylindrical portion. 6. The flash radiography diode of claim 1, wherein the flange is at least partially coated with carbon. 7. The flash radiography diode of claim 1, wherein the frustum member projects from a base of the cathode towards the tapered anode. 8. The flash radiography diode of claim 7, wherein the bore comprises a conical shape comprising a first opening with a first diameter at the first end and a second end with a second diameter, the first diameter smaller than the second diameter and the first end located closer to the tapered anode than the second end. 9. The flash radiography diode of claim 1, wherein the gap comprises an axial gap between the tapered anode and the bore and wherein the axial gap is between 1 and 3 mm. 10. The flash radiography diode of claim 1, wherein the anode comprises a coating element with an atomic number greater than 55. 11. The flash radiography diode of claim 10, wherein the element is tungsten or uranium. 12. The flash radiography diode of claim 1, wherein non-tip portions of the tapered anode comprise a carbon coating configured to increase ion emission threshold. 13. The flash radiography diode of claim 1, wherein non-tip portions of the tapered anode comprise at least one material selected from the group consisting of an element having an atomic number less than 55, carbon, aluminum or titanium, the at least one material configured to increase the ion emission threshold of the anode. 14. The flash radiography diode of claim 1, wherein the bore is coaxial with the tapered anode. 15. The flash radiography diode of claim 1, wherein the tapered anode is replaceable. 16. The flash radiography diode of claim 1, wherein the non-tapered portion of the tapered anode comprises a hollow rod. 17. The flash radiography diode of claim 16, wherein the hollow rod comprises at least one element with an atomic number less than 55. 18. The flash radiography diode of claim 1, wherein the cathode is connected to ground. 19. The flash radiography diode of claim 1, wherein the chamber is an evacuated chamber. 20. The flash radiography diode of claim 1, wherein the cathode comprises a carbon coating or a carbon insert. 21. The flash radiography diode of claim 1, wherein the cathode comprises an anodized aluminum configured to minimize plasma production on the remainder of the cathode. 22. The flash radiography diode of claim 1, further comprising a positive polarity voltage pulse generator coupled to the cathode. 23. A method of operating a flash radiography diode, comprising: providing an electrical pulse from a voltage pulse generator to a cathode; propagating electrons from an outer surface of a frustum member of the cathode across a gap to a tapered anode; emitting an X ray from a tip of the tapered anode through a bore in the cathode, the bore comprising a smaller diameter close to the tapered anode and a larger diameter further from the tapered anode; and wherein the frustum member includes a flange having an outwardly flared wall at a first end proximate to the anode. 24. The method of claim 23 further comprising heating the anode. 25. The method of claim 23 further comprising forming plasma on a high-field stressed portion of the frustum member. 26. The method of claim 25, wherein electrons from the plasma strike a tip of the tapered anode. 27. The method of claim 23, wherein propagating electrons comprises electrostatically focusing electrons emitted from the cathode towards a tip of the anode. 28. The method of claim 23 further comprising forming an anode plasma on the tip of the anode because of high electron flux. 29. The method of claim 28 further comprising expanding the anode plasma in a primarily radial direction. 30. A method of generating ions, comprising: providing an electrical pulse from a voltage pulse generator; propagating electrons from a cathode to an anode, the cathode connected to the voltage pulse generator and the anode comprising an element to be ionized; ionizing gas molecules emitted from the anode surface; and wherein the cathode includes a frustum member having a flange with an outwardly flared wall at a first end proximate to the anode. 31. The method of claim 30, wherein the anode comprises a deuterated plastic. 32. The method of claim 31, wherein ionizing gas molecules comprises generating neutrons.