From the discovery of the atomic nucleus its binding energy has been a key observable for understanding nuclear structure. A century later the atomic masses of more than two thousand radionuclides have been measured and the resulting trends of binding energies have shown great sensitivity to the evolution of nuclear structure with the change of proton and neutron number. Nuclear theory concepts such as "shell closures", "nuclear deformation" and "pairing gap" rely heavily on the intuition built with the properties of the mass surface, while nucleosynthesis and weak-interaction studies require nucleon separation energies and beta-decay Q-values as experimental input.
The ISOLTRAP spectrometer has been used for the past three decades to perform mass measurements of exotic nuclides at ISOLDE/CERN. First thought as a Penning-trap experiment, the installation in 2010 of a multi-reflection time-of-flight mass spectrometer (MR-TOF MS) has turned it into a versatile setup capable not only of performing mass measurements, but also ion-counting studies and trap-assisted spectroscopy. Operating most of the times as an MR-TOF MS/Penning-trap tandem, ISOLTRAP has now proven capable of measuring isotopes of less than 50 ms half-life, produced at rates below 10 ions per second.
This talk will give an overview of the current status of the ISOLTRAP setup, its capabilities and recently performed studies in key regions of the nuclear chart. The masses of neutron-rich copper and cadmium isotopes reveal the evolution of the structure of N = 50 and N = 82 isotones towards 78Ni and away from 132Sn, respectively. The masses of neutron-rich A~100 nuclides explore the limits of the "shape-transition" phenomenon in the region, while the masses of neutron-rich chromium isotopes illustrate the sensitivity of the mass surface to the so-called "N = 40 island of inversion".
In addition, the talk will present preliminary results from the implementation of a new ion-phase-imaging technique for high-precision Q-value measurements and high-resolution isomer separation.