Patent Number: 
Section: claims

1. A radiation generator comprising:an insulator;a ion source carried within the insulator and configured to directly generate ions and indirectly generate undesirable particles;a plurality of extractor electrodes, a first extractor electrode of the plurality of extractor electrodes carried within the insulator downstream of the ion source and having a first potential, and a second extractor electrode of the plurality of extractor electrodes carried within the insulator downstream of the ion source and having a second potential, wherein the first extractor electrode terminates farther downstream from the ion source than the second extractor electrode, and wherein the first potential is closer to ground than the second potential;an intermediate electrode carried within the insulator downstream of the extractor electrodes and being shaped to capture at least some of the undesirable particles;a suppressor electrode carried within the insulator downstream of the intermediate electrode and having a third potential opposite in sign to the first potential and the second potential;the intermediate electrode being at an intermediate potential between the first and third potential; anda target carried within the insulator downstream of the suppressor electrode;the extractor electrodes and the suppressor electrode having a voltage therebetween such that an electric field generated in the insulator accelerates the ions generated by the ion source toward the target. 2. The radiation generator of claim 1, wherein the intermediate potential is at ground potential. 3. The radiation generator of claim 1, wherein the first extractor electrode is curved inwardly toward a longitudinal axis of the insulator and a portion of the first extractor electrode that is curved has a substantially uniform thickness. 4. The radiation generator of claim 1, wherein the suppressor electrode is curved inwardly toward a longitudinal axis of the insulator. 5. The radiation generator of claim 1, wherein the first extractor electrode is shaped to capture the undesirable particles indirectly generated by the ion source, wherein the first extractor electrode is curved inwardly toward a longitudinal axis of the insulator, whereby an inner diameter of the first extractor electrode is greater at a longitudinal location nearer to the ion source than at a longitudinal location farther from the ion source. 6. The radiation generator of claim 1, wherein the intermediate electrode is shaped to attenuate x-rays undesirably generated in the radiation generator. 7. The radiation generator of claim 1, wherein the intermediate electrode is T-shaped. 8. The radiation generator of claim 1, wherein the intermediate electrode comprises a base extending along the longitudinal axis of the insulator, and a projection extending outwardly from the base. 9. The radiation generator of claim 8, wherein the projection has a concave triangular shape. 10. The radiation generator of claim 1, wherein the intermediate electrode comprises a material having a Z of less than or equal to 13. 11. The radiation generator of claim 1, comprising a sealed housing carrying the insulator, and ionizable gas molecules within the sealed housing; andwherein the ion source comprises:a cathode configured to emit electrons;a cathode grid downstream of the cathode;an extractor grid downstream of the cathode grid;the cathode and the cathode grid having a first voltage therebetween such that the electrons emitted by the cathode are accelerated toward the grid and downstream;the cathode grid and the extractor grid having a second voltage therebetween less than the first voltage such that the electrons are decelerated as they approach the extractor grid, at least some of the electrons striking the ionizable gas molecules to create the ions. 12. A well logging instrument comprising:a sonde housing;a radiation generator carried by the sonde housing;a solid insulator carried by the sonde housing between an inner surface of the sonde housing and an outer surface of the radiation generator; andan insulating gas in the sonde housing;the radiation generator comprisinga sealed generator tube,a charged particle source carried within the sealed generator tube and configured to emit charged particles,an extractor electrode carried within the sealed generator tube downstream of the charged particle source at a first potential,an intermediate electrode carried within the sealed generator tube downstream of the extractor electrode wherein the intermediate electrode comprises a base extending along the longitudinal axis of the sealed generator tube, and a projection extending outwardly from the base, wherein the projection comprises a first portion extending from a central point in the base toward the charged particle source and a second portion extending from the central point in the base away from the charged particle source, wherein the first and second portions are substantially symmetrical to each other,a suppressor electrode carried within the sealed generator tube downstream of the intermediate electrode at a second potential opposite in sign to the first potential, anda target within the sealed generator tube downstream of the suppressor electrode,the intermediate electrode being at an intermediate potential between the first and second potential,the difference in the first and second potentials being such that an electric field generated in the sealed generator tube accelerates the charged particles emitted by the charged particle source toward the target;wherein the intermediate electrode curves in a generally complementary trajectory to the extractor electrode and in a generally complementary trajectory to the suppressor electrode, thereby allowing an acceleration gap between the ion source and the target to be shorter than otherwise, and thereby reducing a number of charge exchange reactions that might otherwise occur. 13. The well logging instrument of claim 12, wherein the intermediate potential is a ground potential. 14. The well logging instrument of claim 12, wherein the extractor electrode is curved inwardly toward a longitudinal axis of the sealed generator tube in a direction away from the charged particle source. 15. The well logging instrument of claim 12, wherein the suppressor electrode is curved inwardly toward a longitudinal axis of the sealed generator tube. 16. The well logging instrument of claim 12, wherein the intermediate electrode is T-shaped. 17. The well logging instrument of claim 12, wherein the projection has a concave triangular shape. 18. A method of generating radiation comprising:generating ions and indirectly generating undesirable particles, using an ion source within an insulator, the undesirable particles generated on a trajectory toward the insulator;accelerating the ions toward a target within the insulator using an extractor electrode downstream of the ion source at a first potential and a suppressor electrode downstream of the extractor electrode at a second potential opposite in sign to the first potential; andshielding the insulator from the undesirable particles that would otherwise strike the insulator, using an intermediate electrode downstream of the extractor electrode and upstream of the suppressor electrode at an intermediate potential between the first and second potential and using the extractor electrode, wherein the extractor electrode shields the insulator by curving inwardly toward a longitudinal axis of the insulator away from the ion source, and using the suppressor electrode, wherein the suppressor electrode shields the insulator by curving inwardly toward a longitudinal axis of the insulator toward the ion source, wherein the intermediate electrode curves in a generally complementary trajectory to the extractor electrode and in a generally complementary trajectory to the suppressor electrode, thereby allowing an acceleration gap between the ion source and the target to be shorter than otherwise, and thereby reducing a number of charge exchange reactions that might otherwise occur. 19. The method of claim 18, comprising reducing an electric field that would otherwise be at a surface of the suppressor electrode by shaping the suppressor electrode to be curved inwardly toward a longitudinal axis of the insulator. 20. The method of claim 18, comprising shielding the insulator from the undesirable particles that would otherwise strike the insulator by shaping the extractor electrode to capture the undesirable particles. 21. The method of claim 18, wherein the intermediate electrode comprises a base extending along the longitudinal axis of the housing, and a projection extending outwardly from the base. 22. The method of claim 18, wherein generating the ions comprises:emitting electrons using a cathode; andaccelerating the electrons away from the cathode using a grid downstream of the cathode so that some of the electrons accelerated away from the cathode strike ionizable gas molecules to create the ions.