High-precision mass measurement of doubly magic Pb

The absolute atomic mass of $$ Pb has been determined with a fractional uncertainty of $$ by measuring the cyclotron-frequency ratio R of $$ Pb $$ to $$ Xe $$ with the high-precision Penning-trap mass spectrometer Pentatrap and computing the binding energies $$ and $$ of the missing 41 and 26 atomic electrons, respectively, with the ab initio fully relativistic multi-configuration Dirac-Hartree-Fock (MCDHF) method. R has been measured with a relative precision of $$ . $$ and $$ have been computed with an uncertainty of 9.1 eV and 2.1 eV, respectively, yielding $$  u ( $$  eV/c $$ ) for the $$ Pb neutral atomic mass. This result agrees within $$ with that from the Atomic-Mass Evaluation (AME) 2020, while improving the precision by almost two orders of magnitude. The new mass value directly improves the mass precision of 14 nuclides in the region of Z = 81-84 and is the most precise mass value with $$ . Thus, the measurement establishes a new region of reference mass values which can be used e.g. for precision mass determination of transuranium nuclides, including the superheavies.