Atomic mass determination of uranium-238

Abstract

The atomic mass of uranium-238 has been determined to be $238.050787618(15)\text{u}$, improving the literature uncertainty by two orders of magnitude. It is obtained from a measurement of the mass ratio of ${}^{238}$U${}^{47+}$ and ${}^{132}$Xe${}^{26+}$ ions with an uncertainty of $3.5\times 10^{-12}$. The measurement was carried out with the Penning-trap mass spectrometer \textsc{Pentatrap} and was accompanied by a calculation of the binding energies $E_{\text{U}}$ and $E_{\text{Xe}}$ of the 47 and 26 missing electrons of the two highly charged ions, respectively. These binding energies were determined using an \textit{ab initio} multiconfiguration Dirac-Hartree-Fock (MCDHF) method to be $E_{\text{U}}=39927(10)\text{eV}$ and $E_{\text{Xe}}=8971.2(21)\text{eV}$. The new mass value will serve as a reference for high-precision mass measurements in the heavy mass region of the nuclear chart up to transuranium nuclides.

Includes a Supplemental Material