High-precision mass measurement of doubly magic [Formula: see text] Pb

The absolute atomic mass of [Formula: see text] Pb has been determined with a fractional uncertainty of [Formula: see text] by measuring the cyclotron-frequency ratio R of [Formula: see text] Pb[Formula: see text] to [Formula: see text] Xe[Formula: see text] with the high-precision Penning-trap mass spectrometer Pentatrap and computing the binding energies [Formula: see text] and [Formula: see text] 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 [Formula: see text] . [Formula: see text] and [Formula: see text] have been computed with an uncertainty of 9.1 eV and 2.1 eV, respectively, yielding [Formula: see text] u ([Formula: see text] eV/c[Formula: see text] ) for the [Formula: see text] Pb neutral atomic mass. This result agrees within [Formula: see text] 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 [Formula: see text] . 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.