A spectrum of the radiative recombination showing the features
from heliumlike, hydrogenic, and bare uranium ions.

We produced bare uranium ions (U92+) in Super-EBIT. This achievement is the first time these ions have been produced without the use of a high-energy particle accelerator.

The ions were produced in Super-EBIT with an electron beam energy of about 198 keV, well above the binding energy of the most tightly bound electron (that of hydrogenic uranium) of about 131 keV. We detected the ions by means of their emitted radiative recombination. From the intensity of the recombination, we infer that there were about 8 bare uranium ions in the trap at any time.

We also used the radiative recombination to infer the ionization cross section for heliumlike and hydrogenic uranium, as described in our paper on the subject (Phys. Rev. Lett. 72, 4082 (1994)).