Precision Mass Measurements of Neutron-Rich Rare-Earth Nuclei*

One of the open problems in nuclear astrophysics is the identification of the astrophysical site of the rapid neutron capture process (\textit{r} process). Due to the lack of experimental nuclear data of neutron-rich nuclei far from stability, it remains difficult to constrain or judge the accuracy of \textit{r}-process models and calculations. The Canadian Penning Trap mass spectrometer (CPT) is located in the CARIBU facility at Argonne National Laboratory where intense beams of neutron-rich isotopes are created from the spontaneous fission of a $^{252}$Cf source. The implementation of a phase-imaging mass measurement technique (PI-ICR) at the CPT in conjunction with the MR-TOF mass separator at CARIBU has improved our experimental sensitivity by more than two orders of magnitude. Recently, PI-ICR was used to make the first direct mass measurements of a number of neutron-rich rare-earth isotopes near N = 100. The phase-imaging technique, and insights from these new masses into possible \textit{r}-process sites will be discussed.