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High-precision hyperfine structure measurements were performed on stable, singly-charged 59 Co ions at the IGISOL facility in Jyväskylä, Finland using the collinear laser spectroscopy technique. A newly installed light collection setup enabled the study of transitions in the 230 nm wavelength range from low-lying states below 6000 cm - 1 . We report a 100-fold improvement on the precision of the hyperfine A parameters, and furthermore present newly measured hyperfine B paramaters.

We demonstrate that the pulsed-time structure and high-peak ion intensity provided by the laser-ablation process can be directly combined with the high resolution, high efficiency, and low background offered by collinear resonance ionization spectroscopy. This simple, versatile, and powerful method offers new and unique opportunities for high-precision studies of atomic and molecular structures, impacting fundamental and applied physics research. We show that even for ion beams possessing a relatively large energy spread, high-resolution hyperfine-structure measurements can be achieved by correcting the observed line shapes with the time-of-flight information of the resonantly ionized ions. This approach offers exceptional advantages for performing precision measurements on beams with large energy spreads and allows measurements of atomic parameters of previously inaccessible electronic states. The potential of this experimental method in multidisciplinary research is illustrated by performing, for the first time, hyperfine-structure measurements of selected states in the naturally occurring isotopes of indium,In113,115. Ab initio atomic-physics calculations have been performed to highlight the importance of our findings in the development of state-of-the-art atomic many-body methods, nuclear structure, and fundamental-physics studies.

In spite of the high-density and strongly correlated nature of the atomic nucleus, experimental and theoretical evidence suggests that around particular ‘magic’ numbers of nucleons, nuclear properties are governed by a single unpaired nucleon 1 , 2 . A microscopic understanding of the extent of this behaviour and its evolution in neutron-rich nuclei remains an open question in nuclear physics 3 – 5 . The indium isotopes are considered a textbook example of this phenomenon 6 , in which the constancy of their electromagnetic properties indicated that a single unpaired proton hole can provide the identity of a complex many-nucleon system 6 , 7 . Here we present precision laser spectroscopy measurements performed to investigate the validity of this simple single-particle picture. Observation of an abrupt change in the dipole moment at N  = 82 indicates that, whereas the single-particle picture indeed dominates at neutron magic number N  = 82 (refs.  2 , 8 ), it does not for previously studied isotopes. To investigate the microscopic origin of these observations, our work provides a combined effort with developments in two complementary nuclear many-body methods: ab initio valence-space in-medium similarity renormalization group and density functional theory (DFT). We find that the inclusion of time-symmetry-breaking mean fields is essential for a correct description of nuclear magnetic properties, which were previously poorly constrained. These experimental and theoretical findings are key to understanding how seemingly simple single-particle phenomena naturally emerge from complex interactions among protons and neutrons. Precision laser spectroscopy measurements of neutron-rich indium isotopes were performed to investigate the validity and identify limitations of theoretical descriptions of nuclei based on simple single-particle approaches.

Understanding the evolution of the nuclear charge radius is one of the long-standing challenges for nuclear theory. Recently, density functional theory calculations utilizing Fayans functionals have successfully reproduced the charge radii of a variety of exotic isotopes. However, difficulties in the isotope production have hindered testing these models in the immediate region of the nuclear chart below the heaviest self-conjugate doubly-magic nucleus 100 Sn, where the near-equal number of protons ( Z ) and neutrons ( N ) lead to enhanced neutron-proton pairing. Here, we present an optical excursion into this region by crossing the N = 50 magic neutron number in the silver isotopic chain with the measurement of the charge radius of 96 Ag ( N = 49). The results provide a challenge for nuclear theory: calculations are unable to reproduce the pronounced discontinuity in the charge radii as one moves below N = 50. The technical advancements in this work open the N = Z region below 100 Sn for further optical studies, which will lead to more comprehensive input for nuclear theory development. Laser spectroscopic measurements of isotopes near the doubly-magic 100-Sn are challenging due to difficulties in their production. Here the authors measure the ground state charge radius of the proton-rich 96-Ag isotope and find a discontinuity in the nuclear size when crossing the neutron number N equal to 50.

A review is given of precision measurements of hyperfine constants and nuclear g-factors measured with ions confined in ion traps. The nuclear physics observables which can be extracted from these types of measurements are discussed. The feasibility of future nuclear structure studies using precision atomic spectroscopy of trapped radioactive atoms, produced with accelerator-driven approaches, is discussed.

High-resolution collinear laser spectroscopy has been performed on singly charged ions of 234 , 235 , 238 U at the IGISOL facility of the Accelerator Laboratory, University of Jyväskylä, in Finland. Ten ionic transitions from the 4 I 9 / 2 and 6 L 11 / 2 ground and first excited states were measured in the 300 nm wavelength range, improving the precision of the hyperfine parameters of the lower states in addition to providing newly measured values for the upper levels. Isotope shifts of the analyzed transitions are also reported for 234 , 235 U with respect to 238 U.

With increasing demand for accurate calculation of isotope shifts of atomic systems for fundamental and nuclear structure research, an analytic energy derivative approach is presented in the relativistic coupled-cluster (CC) theory framework to determine the atomic field shift and mass shift (MS) factors. This approach allows the determination of expectation values of atomic operators, overcoming fundamental problems that are present in existing atomic physics methods, i.e. it satisfies the Hellmann-Feynman theorem, does not involve any non-terminating series, and is free from choice of any perturbative parameter. As a proof of concept, the developed analytic response relativistic CC theory has been applied to determine MS and field shift factors for different atomic states of indium. High-precision isotope-shift measurements of 104 − 127 In were performed in the 246.8 nm (5p 2P3/2 → 9s 2S1/2) and 246.0 nm (5p 2P1/2 → 8s 2S1/2) transitions to test our theoretical results. An excellent agreement between the theoretical and measured values is found, which is known to be challenging in multi-electron atoms. The calculated atomic factors allowed an accurate determination of the nuclear charge radii of the ground and isomeric states of the 104 − 127 In isotopes, providing an isotone-independent comparison of the absolute charge radii.

This paper reports on the hyperfine-structure and radioactive-decay studies of the neutron-deficient francium isotopes Fr202–206 performed with the Collinear Resonance Ionization Spectroscopy (CRIS) experiment at the ISOLDE facility, CERN. The high resolution innate to collinear laser spectroscopy is combined with the high efficiency of ion detection to provide a highly sensitive technique to probe the hyperfine structure of exotic isotopes. The technique of decay-assisted laser spectroscopy is presented, whereby the isomeric ion beam is deflected to a decay-spectroscopy station for alpha-decay tagging of the hyperfine components. Here, we present the first hyperfine-structure measurements of the neutron-deficient francium isotopes Fr202–206 , in addition to the identification of the low-lying states of Fr202,204 performed at the CRIS experiment.

Nuclear charge radii globally scale with atomic mass number A as A 1∕3 , and isotopes with an odd number of neutrons are usually slightly smaller in size than their even-neutron neighbours. This odd–even staggering, ubiquitous throughout the nuclear landscape 1 , varies with the number of protons and neutrons, and poses a substantial challenge for nuclear theory 2 – 4 . Here, we report measurements of the charge radii of short-lived copper isotopes up to the very exotic 78 Cu (with proton number Z = 29 and neutron number N = 49), produced at only 20 ions s –1 , using the collinear resonance ionization spectroscopy method at the Isotope Mass Separator On-Line Device facility (ISOLDE) at CERN. We observe an unexpected reduction in the odd–even staggering for isotopes approaching the N = 50 shell gap. To describe the data, we applied models based on nuclear density functional theory 5 , 6 and A -body valence-space in-medium similarity renormalization group theory 7 , 8 . Through these comparisons, we demonstrate a relation between the global behaviour of charge radii and the saturation density of nuclear matter, and show that the local charge radii variations, which reflect the many-body polarization effects, naturally emerge from A -body calculations fitted to properties of A ≤ 4 nuclei. Isotopes with an odd number of neutrons are usually slightly smaller in size than their even-neutron neighbours. In charge radii of short-lived copper isotopes, a reduction of this effect is observed when the neutron number approaches fifty.

Nuclear charge radii are sensitive probes of different aspects of the nucleon–nucleon interaction and the bulk properties of nuclear matter, providing a stringent test and challenge for nuclear theory. Experimental evidence suggested a new magic neutron number at N = 32 (refs. 1–3) in the calcium region, whereas the unexpectedly large increases in the charge radii4,5 open new questions about the evolution of nuclear size in neutron-rich systems. By combining the collinear resonance ionization spectroscopy method with β-decay detection, we were able to extend charge radii measurements of potassium isotopes beyond N = 32. Here we provide a charge radius measurement of 52K. It does not show a signature of magic behaviour at N = 32 in potassium. The results are interpreted with two state-of-the-art nuclear theories. The coupled cluster theory reproduces the odd–even variations in charge radii but not the notable increase beyond N = 28. This rise is well captured by Fayans nuclear density functional theory, which, however, overestimates the odd–even staggering effect in charge radii. These findings highlight our limited understanding of the nuclear size of neutron-rich systems, and expose problems that are present in some of the best current models of nuclear theory.The charge radii of potassium isotopes up to 52K are measured, and show no sign of magicity at 32 neutrons as previously suggested in calcium. The observations are interpreted with coupled cluster and density functional theory calculations.