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 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 fully relativistic multi-configuration Dirac-Hartree-Fock (MCDHF) method. 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 (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 = 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.