New Nuclear Magnetic Moment of 209Bi: Resolving the Bismuth Hyperfine Puzzle

A recent measurement of the hyperfine splitting in the ground state of Li-like Bi-208(80+) has established a "hyperfine puzzle"- the experimental result exhibits a 7 sigma deviation from the theoretical prediction [J. Ullmann et al., Nat. Commun. 8, 15484 (2017); J. P. Karr, Nat. Phys. 13, 533 (2017)]. We provide evidence that the discrepancy is caused by an inaccurate value of the tabulated nuclear magnetic moment (mu(I)) of Bi-209. We perform relativistic density functional theory and relativistic coupled cluster calculations of the shielding constant that should be used to extract the value of mu(l) (Bi-209) and combine it with nuclear magnetic resonance measurements of BioNO(NO3)(3) in nitric acid solutions and of the hexafluoridobismuthate (V) BiF6- ion in acetonitrile. The result clearly reveals that mu(l) (Bi-209) is much smaller than the tabulated value used previously. Applying the new magnetic moment shifts the theoretical prediction into agreement with experiment and resolves the hyperfine puzzle.