Masahiro Tooma

Origins of charged particles in vapor generated by electron‐beam evaporation

The origins of electrons and ions in uranium vapor generated by electron‐beam evaporation have been determined. Measurements were made for the electron emission current due to high‐energy electron‐beam irradiation on a uranium surface (backscattered electrons, etc.), thermionic emission current from the melt surface, and electron current due to vapor ionization. Comparison of these currents confirmed that vapor ionization was the main electron generation process at evaporation surface temperatures above 2200 K. The ionized vapor formed a weakly ionized plasma of very low electron temperature: The degree of ionization ≤1%, electron temperature ≤0.3 eV. The electron‐impact ionization process contributed mainly to plasma formation. Beam electrons, their backscattered electrons, and secondary electrons from the beam‐irradiated uranium surface were the source electrons for this process. Thermal ionization was the next major process. In addition to the plasma formation model, plasma behavior in vapor was descri...

Cross sections of charge transfer between uranium atoms and ions produced by autoionization

A technique to reduce charge transfer has been studied to cut enrichment loss during atomic vapor laser isotope separation. The charge transfer cross sections of uranium were experimentally examined. The cross sections of charge transfer for case A (between ground-state ions and atoms) and, cases B and C (between ions populated in some excited states and atoms) were relatively measured in the energy range of 100–2,000 eV by the cross-beam method. The charge transfer cross sections for cases A, B and C do not depend on impact energy, and the cross sections for case A are smaller than those for cases B and C. These results are in fairly good agreement agreed with theoretical predictions. It is confirmed experimentally and theoretically that the uranium charge transfer cross section depends on its initial ionic state, therefore ion loss by charge transfer will be reduced by controlling the initial state of the ions.