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

Abstract

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 147Er and 148Er 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 232Ra 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.