Schottky mass measurements of cooled nuclei and mass landscape of the new area of neutron-deficient sub-uranium nuclides

A novel method for direct, high precision mass measurements of relativistic exotic nuclei has been successfully applied in the storage ring ESR at GSI. The nuclei of interest were produced by projectile fragmentation of relativistic highly charged gold and bismuth ions. Products of reactions were separated in-flight by the fragment separator FRS, stored and electron cooled in the storage ring ESR. The mass values have been deduced from the revolution frequencies of the cooled circulating ions, which have been measured by Schottky diagnosis via a Fourier transform of the Schottky noise signal. The main bulk of information have been obtained by fragmentation of 930 MeV/u bismuth ions and is described in this report. The masses for 104 neutron-deficient nuclides of the elements 57 ≤ Z ≤ 84 have been measured for the first time. The precision of mass data obtained is ∼ 100 keV. Using experimentally known energies of α-transitions linking the measured nuclides with long α-decay chains we obtained the masses of further short-lived exotic nuclides in addition and, thus, extended the mass determination to the large area of the nuclear chart up to exotic neutron-deficient sub-uranium nuclides. In total the mass values for 168 nuclides have been determined for the first time. The masses for 60 isomeric states with unknown so far excitation energies have been evaluated as well. This new large scale information obtained about masses allows a new look to the particular features of physics in the exotic territory of the chart of nuclides. One- and two-proton drip-lines have been identified. No evidence for a Thomas-Ehrman shift which could perturb the position of drip-lines has been observed in the region of heavy nuclides. The size of the ''littoral shallow'' of the sea of instability were outlined for the heavy mass region. The analysis of information on the new masses shows a washing out of the two-proton separation energy gap for lead nuclides far off the β-stability. The predictive power of various mass models has been tested. The result is that neither of mass formula tested yields mass values for exotic neutron-deficient nuclides with an accuracy better than 400 keV. The potential of Schottky mass spectrometry in the future has been discussed. (orig.)