Abstract
Using a novel concept for efficient laser spectroscopy, we investigated the hyperfine splittings of three different atomic transitions in the long-lived isotopes $^{97\ensuremath{-}99}\mathrm{Tc}$. Despite the refractory character of the element technetium, sample sizes as low as ${10}^{11}$ atoms were sufficient to achieve excellent signal-to-noise ratios at a spectroscopic linewidth of less than 100 MHz. The obtained spectra were analyzed in detail, which results in a very good consistency for the extracted hyperfine parameters from the different transitions. The presented measurements provide the first hyperfine structure data for the isotopes $^{97,98}\mathrm{Tc}$ from which, in combination with the known nuclear moments of $^{99}\mathrm{Tc}$, their nuclear magnetic dipole and electric quadrupole moments were extracted. In addition, the experimental data confirm the predicted nuclear spin of $^{98}\mathrm{Tc}$ to $I=6$. In combination with atomic Multiconfiguration Dirac-Hartree-Fock calculations, the observed isotope shifts were investigated and the changes in mean-square charge radii were determined.
Highlights
Technetium (Z = 43) is the lightest element with exclusively radioactive isotopes
Using a novel concept for efficient laser spectroscopy, we investigated the hyperfine splittings of three different atomic transitions in the long-lived isotopes 97−99Tc
We investigated the hyperfine structure (HFS) in transitions of the odd-mass isotopes 97Tc and 99Tc with resonance ionization spectroscopy (RIS) [18], while in this work the measurement and evaluation were refined using three different
Summary
99gTc features a fission yield of about 6%, and technetium poses a substantial amount of the long-lived nuclear waste. The refractory character of the transition metal technetium, as well as the limited information on the atomic structure impeded laser spectroscopic investigations of Tc isotopes, especially at isotope separator on-line (ISOL) facilities. In several low-lying multiplets the hyperfine structure (HFS) was partly resolved and investigated by Wendlandt et al [9], but only for the isotope 99Tc. for the long-lived isotopes the nuclear magnetic dipole moment was studied only for 99Tc by different techniques [9,10,11,12], while the most accurate value of μ(99Tc) = 5.6847(4) μN is based on nuclear magnetic resonance (NMR) measurements by Walchli et al [10]. Besides the information of the nuclear properties of the technetium isotopes, the presented results foster the current Tc trace analysis project at Mainz University [19,20,21], where the spectroscopic information on 97Tc is essential for using this isotope as tracer
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