Observation of an unexpected negative isotope shift in 229Th+ and its theoretical explanation

Abstract

We have measured the hyperfine structure and isotope shifts of the 402.0 nm and 399.6 nm resonance lines in 229Th+. These transitions could provide pathways towards the 229Th isomeric nuclear state excitation. An unexpected negative isotope shift relative to 232Th+ is observed for the 399.6 nm line, indicating a strong Coulomb coupling of the excited state to the nucleus. We have developed a new all-order approach to the isotope shift calculations that is generally applicable to heavy atoms and ions with several valence electrons. The theoretical calculations provide an explanation for the negative isotope shift of the 399.6 nm transition and yield a corrected classification of the excited state. The calculated isotope shifts are in good agreement with experimental values.

arXiv comment5 pages, 2 figures

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Cited by in corpus (9)

• Radiative lifetime and energy of the low-energy isomeric level in ${}^{229}$Th
• The ${}^{229}$Th isomer: prospects for a nuclear optical clock
• Nuclear charge radii of ${}^{229}$Th from isotope and isomer shifts
• Internal conversion from excited electronic states of ${}^{229}\mathrm{T}h$ ions
• Hyperfine interaction with the ${}^{229}$Th nucleus and its low lying isomeric state
• Theoretical analysis of the electron bridge process in ${}^{229}$Th${}^{3+}$
• Electronic level structure of ${\mathrm{Th}}^{+}$ in the range of the ${}^{229m}\mathrm{Th}$ isomer energy
• Sympathetic cooling of trapped Th3+ alpha-recoil ions for laser spectroscopy
• Shift of nuclear clock transition frequency in ${}^{229}$Th ions due to hyperfine interaction