Searching for the origin of the rare-earth peak with precision mass measurements across Ce–Eu isotopic chains

R. Orford, N. Vassh, J. Clark, G. C. McLaughlin, M. Mumpower, D. Ray, G. Savard, R. Surman, F. Buchinger, D. P. Burdette, M. T. Burkey, D. A. Gorelov, J. W. Klimes, W. S. Porter, K. S. Sharma, A. A. Valverde, L. Varriano, X. L. Yan

Published PRCL 105, 052802 (2022)

A nuclear mass survey of rare-earth isotopes has been conducted with the Canadian Penning Trap mass spectrometer using the most neutron-rich nuclei thus far extracted from the CARIBU facility. We present a collection of 12 nuclear masses determined with a precision of less than 10 keV/$c^2$ for $Z=58 - 63$ nuclei near $N = 100$. Independently, a detailed study exploring the role of nuclear masses in the formation of the r-process rare-earth abundance peak has been performed. Employing a Markov chain Monte Carlo (MCMC) technique, mass predictions of lanthanide isotopes have been made which uniquely reproduce the observed solar abundances near $A = 164$ under three distinct astrophysical outflow conditions. We demonstrate that the mass surface trends thus far mapped out by our measurements are most consistent with MCMC mass predictions given an r process that forms the rare-earth peak during an extended (n,$\gamma$)-($\gamma$,n) equilibrium.