Precision mass measurements of neutron-rich nuclides using the Canadian Penning Trap mass spectrometer for studying the astrophysical r process*

The formation of about half of the nuclides with Z>26 is attributed to the astrophysical r process, of which our knowledge is still limited. Building models to reproduce the r-process elemental abundances relies on nuclear data with reduced uncertainties for these neutron-rich nuclides. Such data exist in limited quantity due to the difficulties in accessing those nuclides. Masses are an important input to such models. The CARIBU facility, at Argonne National Laboratory can produce beams of such neutron-rich nuclides using the spontaneous fission of a ²⁵²Cf source. The fragments are collected, cooled, bunched and purified, before being sent to the Canadian Penning Trap (CPT) mass spectrometer, where their masses are measured using the Phase-Imaging Ion-Cyclotron-Resonance (PI-ICR) technique. PI-ICR at the CPT has permitted mass measurements of long-lived isomers as well as weakly-produced nuclides from ²⁵²Cf fission, while regularly achieving precision of <5 keV/c². A brief description of the apparatus and recent results will be presented.