Atom-at-a-time laser resonance ionization spectroscopy of nobelium


Optical spectroscopy of a primordial isotope has traditionally formed the basis for understanding the atomic structure of an element. Such studies have been conducted for most elements1 and theoretical modelling can be performed to high precision2,3, taking into account relativistic effects that scale approximately as the square of the atomic number. However, for the transfermium elements (those with atomic numbers greater than 100), the atomic structure is experimentally unknown. These radioactive elements are produced in nuclear fusion reactions at rates of only a few atoms per second at most and must be studied immediately following their production4, which has so far precluded their optical spectroscopy. Here we report laser resonance ionization spectroscopy of nobelium (No; atomic number 102) in single-atom-at-a-time quantities, in which we identify the ground-state transition 1S0 1P1. By combining this result with data from an observed Rydberg series, we obtain an upper limit for the ionization potential of nobelium. These accurate results from direct laser excitations of outer-shell electrons cannot be achieved using state-of-the-art relativistic many-body calculations5,6,7,8 that include quantum electrodynamic effects, owing to large uncertainties in the modelled transition energies of the complex systems under consideration. Our work opens the door to high-precision measurements of various atomic and nuclear properties of elements heavier than nobelium, and motivates future theoretical work.

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Figure 1: Resonance ionization signals of nobelium atoms.
Figure 2: Saturation characteristics of the first-step resonance for 254No.
Figure 3: Observed high-lying Rydberg states in nobelium.


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We thank the staff of the GSI ion source and accelerator for the preparation of a stable 48Ca beam and the staff of the target laboratory for providing high-quality targets. We acknowledge the technical support of J. Maurer, H. G. Burkhard, D. Racano, L. Braisz, D. Reemts, C. Droese, B. Schausten and I. Kostyuk. We thank P. Thirolf for his suggestions and comments. This work was supported by the German Federal Ministry of Education and Research under contracts 06MZ169I, 06LM236I, FAIR NuSTAR 05P09RDFN4, 05P12RDFN8 and 05P15RDFN1; by the GSI; and by the Helmholtz-Institut Mainz.

Author information

W.L., H.B., M.B., T.W., P.v.D., C.E.D., M.H. and A.Y. provided experimental equipment. M.L., F.L., P.C., S.R., W.L., P.K., M.B., F.P.H., D.A., C.W., A.K.M., B.C., R.F., F.G., O.K., J.K., J.E., S.G. and E.M.R. performed the experiments. F.L., P.C., H.B., S.R. and M.L. analysed the data. M.L. wrote the manuscript with input from all authors.

Correspondence to Mustapha Laatiaoui.

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The authors declare no competing financial interests.

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Nature thanks V. Fedosseev and L. Visscher for their contribution to the peer review of this work.

Extended data figures and tables

Extended Data Figure 1 Principle of the RADRIS technique.

Laser spectroscopy on radionuclides (spheres) after their production and transmission through the velocity filter SHIP22. a, Thermalization of the fusion products in the buffer gas; b, accumulation on the catcher filament; c, re-evaporation from the filament; d, two-step photoionization of neutral atoms; e, accumulation of re-ionized fusion products on the PIPS detector; f, decay detection.

Extended Data Table 1 Uncertainties on the value of the 254No first-step resonance

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Laatiaoui, M., Lauth, W., Backe, H. et al. Atom-at-a-time laser resonance ionization spectroscopy of nobelium. Nature 538, 495–498 (2016).

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