Charge-exchange cross sections and beam lifetimes for stored and decelerated bare uranium ions

Charge-exchange cross sections and beam lifetimes are studied for decelerated bare uranium ions at the ESR storage ring. By deceleration from the initial energy of 358 MeV/u down to various energies as low as 49 MeV/u, i.e., far below the production energy of bare ionic species, the electron pickup cross sections were obtained for collisions with N₂, Ar, CH₄, and Kr gaseous targets. The measured cross sections and beam lifetimes are compared with the theoretical results for radiative and nonradiative electron capture. The present data, along with the theoretical approximations discussed, provide a solid basis for the estimation of beam lifetimes for decelerated bare high-Z ions. Moreover, a normalization procedure is proposed, in which absolute total charge-exchange cross sections are derived by normalizing the simultaneously measured yield of radiative electron capture photons to rigorously calculated relativistic cross sections. This method, along with the unprecedented beam conditions at the ESR storage ring, allows a significant improvement of the accuracy of cross-section data.