Measurement of QED and Hyperfine Splitting in the2s1/2-2p3/2X-Ray Transition in Li-likeB209i80+

A measurement of the ${2s}_{1/2}-{2p}_{3/2}$ x-ray transition in trapped Li-like ${\mathrm{Bi}}^{80+}$ ions was made that resolved the $0.820\pm 0.026\mathrm{eV}$ hyperfine splitting of the $({1s}^{2}2s{)}_{F=4,5\mathrm{}}$ ground configuration, providing the first such measurement in a multielectron highly charged ion. The intensity ratio of the two components is shown to be a new electron density diagnostic. The statistically averaged $2788.139\pm 0.039\mathrm{eV}$ energy of the ${2s}_{1/2}-{2p}_{3/2}$ transition provides the most accurate test of QED in a high- $Z$ ion to date, demonstrating the need for including higher-order terms in the Lamb shift calculations.