First on-line mass measurements at SHIPTRAP and mass determinations of neutron-rich Fr and Ra isotopes at ISOLTRAP

SHIPTRAP is an ion trap facility behind the velocity filter SHIP at GSI/Darmstadt. Its aim are precision studies of transuranium nuclides produced in a fusion reaction and separated by SHIP. The current set-up for high-precision mass measurements consists of three main functional parts: (i) a gas cell for stopping the energetic ions from SHIP, (ii) radiofrequency quadrupole structures to cool and to bunch the ions extracted from the gas cell, and (iii) a superconducting magnet with two cylindrical Penning traps at a field strength of 7 T. In this work the Penning trap system has been installed and extensively characterized. The first on-line mass measurements of short-lived nuclides were carried out and the masses of $^{147}$Er and $^{148}$Er could be experimentally determined for the first time. Here a relative mass uncertainty of $\delta$ m/m of about 1$\times$ 10$^{-6}$ was achieved. Furthermore the masses of heavy neutron-rich $^{229-232}$Ra and $^{230}$Fr isotopes have been determined with a relative mass uncertainty of about 1$\times$10$^{-7}$ with the ISOLTRAP mass spectometer at ISOLDE/CERN. The isotope $^{232}$Ra is the heaviest unstable nuclide ever investigated with a Penning trap. Underlying nuclear structure effects of these nuclides far from$\beta$-stability were studied by a comparison of the resulting two-neutron separation energies S$_{2n}$ with those given by the theoretical Infinite nuclear mass model.