Schottky Mass Measurements of Cooled Proton-Rich Nuclei at the GSI Experimental Storage Ring

High-precision mass measurements of proton-rich isotopes in the range of 60≤Z≤84 were performed using the novel technique of Schottky spectrometry. Projectile fragments produced by ²⁰⁹Bi ions at 930A MeV were separated with the magnetic spectrometer FRS and stored and cooled in the experimental storage ring (ESR). A typical mass resolving power of 350 000 and a precision of 100 keV were achieved in the region A≈200. Masses of members of α chains linked by precise Q_α values but not yet connected to the known masses were determined. In this way it is concluded that ²⁰¹Fr and ¹⁹⁷At are proton unbound.