High-precision mass measurement of doubly magic $^{208}$Pb

TL;DR

This paper reports a highly precise measurement of the atomic mass of doubly magic $^{208}$Pb using advanced Penning-trap mass spectrometry and relativistic calculations, significantly improving existing mass data.

Contribution

The study introduces a novel combination of high-precision Penning-trap measurements with ab initio relativistic calculations to determine the $^{208}$Pb mass with unprecedented accuracy.

Findings

Mass of $^{208}$Pb determined with fractional uncertainty of $7\times 10^{-11}$.

Measurement agrees within $1.2\sigma$ with previous data, but with nearly two orders of magnitude better precision.

Provides a new reference mass value for $^{208}$Pb and improves mass data for related nuclides.

Abstract

The absolute atomic mass of $^{208}$Pb has been determined with a fractional uncertainty of $7\times 10^{-11}$ by measuring the cyclotron-frequency ratio $R$ of $^{208}$Pb$^{41+}$ to $^{132}$Xe$^{26+}$ with the high-precision Penning-trap mass spectrometer Pentatrap and computing the binding energies $E_{\text{Pb}}$ and $E_{\text{Xe}}$ 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 $9\times 10^{-12}$. $E_{\text{Pb}}$ and $E_{\text{Xe}}$ have been computed with an uncertainty of 9.1 eV and 2.1 eV, respectively, yielding $207.976\,650\,571(14)$ u (u$=9.314\,941\,024\,2(28)\times 10^{8}$ eV/c$^2$) for the $^{208}$Pb neutral atomic mass. This result agrees within $1.2\sigma$ 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 A>200. 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.