High-precision mass measurement of doubly magic Pb.

Area of Science:

• Nuclear Physics
• Atomic Physics
• Metrology

Background:

• Accurate atomic mass determination is fundamental for nuclear structure studies and the understanding of fundamental forces.
• Previous measurements of lead-208 atomic mass had limitations in precision, impacting related nuclear data.

Purpose of the Study:

• To determine the absolute atomic mass of lead-208 (²⁰⁸Pb) with unprecedented fractional uncertainty.
• To establish a new high-precision reference mass value for nuclides in the Z = 81-84 region.

Main Methods:

• Measured the cyclotron-frequency ratio (R) of ²⁰⁸Pb to Xenon-136 (¹³⁶Xe) using the Pentatrap high-precision Penning-trap mass spectrometer.
• Computed binding energies of atomic electrons for ²⁰⁸Pb and ¹³⁶Xe using the ab initio fully relativistic multi-configuration Dirac-Hartree-Fock (MCDHF) method.

Main Results:

• Determined the absolute atomic mass of ²⁰⁸Pb with a fractional uncertainty of 1.1 x 10⁻¹¹.
• Achieved a relative precision of 7.1 x 10⁻¹² for the cyclotron-frequency ratio measurement.
• The new mass value improves the precision of 14 nuclides and aligns with the Atomic-Mass Evaluation (AME) 2020 within 0.4σ.

Conclusions:

• The precise determination of ²⁰⁸Pb atomic mass sets a new benchmark for mass metrology.
• This result serves as a critical reference for precision mass determination of transuranium and superheavy nuclides.
• The study highlights the synergy between high-precision Penning-trap measurements and advanced relativistic quantum chemical calculations.