Precision calculations of the hyperfine constants and isotope and isomer shifts in low-lying states of 229Th3+

Abstract

We present high-precision calculations of the hyperfine constants, isotope shift, and isomer shift in low-lying states of Th3+ relevant to spectroscopy of the 229Th nuclear isomer. The removal energy and hyperfine constants are calculated using a relativistic coupled-cluster method including single, double, and triple excitations, demonstrating the importance of higher-order correlation effects. The isotope shift of the 5f_5/2 -7s transition is evaluated using both the CI+MBPT and CI+all-order methods, providing an estimate of the theoretical uncertainty. We find that the isotope shift is dominated by the field shift, with the mass shift contributing negligibly. Combining the calculated field-shift coefficient with the measured difference in the nuclear mean-square charge radii of the ground and isomeric states, we predict the 7s isomer shift to be (Delta E^(m,g))= 0.9(1) GHz. These results provide benchmark atomic data for Th3+ and support ongoing precision spectroscopy of 229Th and the development of a nuclear clock.