Structural trends in atomic nuclei from laser spectroscopy of tin

Tin is the chemical element with the largest number of stable isotopes. Its complete proton shell, comparable with the closed electron shells in the chemically inert noble gases, is not a mere precursor to extended stability; since the protons carry the nuclear charge, their spatial arrangement also drives the nuclear electromagnetism. We report high-precision measurements of the electromagnetic moments and isomeric differences in charge radii between the lowest 1/2(+), 3/2(+), and 11/2(-) states in Sn117-131, obtained by collinear laser spectroscopy. Supported by state-of-the-art atomic-structure calculations, the data accurately show a considerable attenuation of the quadrupole moments in the closed-shell tin isotopes relative to those of cadmium, with two protons less. Linear and quadratic mass-dependent trends are observed. While microscopic density functional theory explains the global behaviour of the measured quantities, interpretation of the local patterns demands higher-fidelity modelling. Measurements of the hyperfine structure of chemical elements isotopes provide unique insight into the atomic nucleus in a nuclear model-independent way. The authors present collinear laser spectroscopy data obtained at the CERN ISOLDE and measure hyperfine splitting along a long chain of odd-mass tin isotopes.Peer reviewe

Impact of buffer gas quenching on the S-1(0) -> P-1(1) ground-state atomic transition in nobelium

International audienceUsing the sensitive Radiation Detected Resonance Ionization Spectroscopy (RADRIS) techniquean optical transition in neutral nobelium (No, Z = 102) was identified. A remnant signal when delaying the ionizing laser indicated the influence of a strong buffer gas induced de-excitation of the optically populated level. A subsequent investigation of the chemical homologue, ytterbium (Yb, Z = 70), enabled a detailed study of the atomic levels involved in this process, leading to the development of a rate equation model. This paves the way for characterizing resonance ionization spectroscopy (RIS) schemes used in the studyof nobelium and beyond, where atomic properties are currently unknown

Quadrupole moments of odd-A ⁵³⁻⁶³Mn: Onset of collectivity towards N = 40

The spectroscopic quadrupole moments of the odd–even Mn isotopes between N=28 and N=38 have been measured using bunched-beam collinear laser spectroscopy at ISOLDE, CERN. In order to increase sensitivity to the quadrupole interaction, the measurements have been done using a transition in the ion rather than in the atom, with the additional advantage of better spectroscopic efficiency. Since the chosen transition is from a metastable state, optical pumping in ISOLDE’s cooler and buncher (ISCOOL) was used to populate this state. The extracted quadrupole moments are compared to large-scale shell model predictions using three effective interactions, GXPF1A, LNPS and modified A3DA. The inclusion of both the 1νg9/2and 2νd5/2orbitals in the model space is shown to be necessary to reproduce the observed increase in the quadrupole deformation from N=36 onwards. Specifically, the inclusion of the 2νd5/2orbital induces an increase in neutron and proton excitations across the reduced gaps at N=40and Z=28, leading to an increase in deformation above N=36

Nuclear charge radii of ⁶²⁻⁸⁰Zn and their dependence on cross-shell proton excitations

Nuclear charge radii of ⁶²⁻⁸⁰Zn have been determined using collinear laser spectroscopy of bunched ion beams at CERN-ISOLDE. The subtle variations of observed charge radii, both within one isotope and along the full range of neutron numbers, are found to be well described in terms of the proton excitations across the Z = 28 shell gap, as predicted by large-scale shell model calculations. It comprehensively explains the changes in isomer-to-ground state mean square charge radii of ⁶⁹⁻⁷⁹Zn, the inversion of the odd-even staggering around N = 40 and the odd-even staggering systematics of the Zn charge radii. With two protons above Z = 28, the observed charge radii of the Zn isotopic chain show a cumulative effect of different aspects of nuclear structure including single particle structure, shell closure, correlations and deformations near the proposed doubly magic nuclei, ⁶⁸Ni and ⁷⁸Ni

The Evolution of Nuclear Structure in Odd-A Zinc Isotopes

The hyperfine spectra of odd-A Zn (Z = 30) isotopes from N = 33 − 49 have been mea- sured using collinear laser spectroscopy at the COLLAPS (COLlinear LAser sPectroScopy) experiment at ISOLDE, CERN. From the hyperfine spectra, nuclear spins I, magnetic dipole moments µ and spectroscopic quadrupole moments Qs were determined across the Zn isotope chain, with isotopes ranging from stability to neutron-rich nuclei approaching N = 50. The 4s4p 3P2o → 4s5s 3S1 atomic transition was probed using a CW laser tuned to 481.1873 nm wavelength, and allowed for maximal sensitivity to the nuclear spin in order to unam- biguously confirm the ground and isomeric state spins of 73−79Zn. The nuclear moments of Zn isotopes were determined using the reference isotope 67Zn and the hyperfine coeffi- cients A(3P2) = +531.987(5) MHz and B(3P2) = +35.806(5) MHz, and reference moments µ = +0.875479(9)µN and Qs = +0.122(10) b, the latter of which is introduced in this work based on new electric field gradient (EFG) calculations. The nuclear moments are compared to predictions from large-scale shell model calculations in the f5pg9 (JUN45 and jj44b) and pfg9d5 (A3DA-m and LNPS-m) model spaces. The improvement of magnetic dipole moment predictions from JUN45 over those from A3DA-m and LNPS-m as N = 50 is approached points to the persistence of the N = 50 shell gap in neutron-rich Zn isotopes. Regarding quadrupole moments, the close agreement between measured Qs values and A3DA-m predictions beyond N = 40 highlights the importance of the νd5/2 orbital for characterising quadrupole deformation. The hyperfine structure of the newly-discovered isomer in 79Zn with tentatively assigned spin-parity of Iπ = 1/2+ has been directly observed for the first time in this work. In order to reproduce its measured nuclear properties, a novel interaction with an extended model space, PFSDG-U, is developed to understand the contributions to the nuclear wave function from np-mh excitations across the N = 50 shell closure

Evolution of nuclear structure in neutron-rich odd-Zn isotopes and isomers

Collinear laser spectroscopy was performed on Zn (Z = 30) isotopes at ISOLDE, CERN. The study of hyperfine spectra of nuclei across the Zn isotopic chain, N = 33–49, allowed the measurement of nuclear spins for the ground and isomeric states in odd-A neutron-rich nuclei up to N = 50. Exactly one longlived (>10 ms) isomeric state has been established in each 69–79Zn isotope. The nuclear magnetic dipole moments and spectroscopic quadrupole moments are well reproduced by large-scale shell–model calculations in the f5pg9 and fpg9d5 model spaces, thus establishing the dominant term in their wave function. The magnetic moment of the intruder Iπ = 1/2+ isomer in 79Zn is reproduced only if the νs1/2 orbital is added to the valence space, as realized in the recently developed PFSDG-U interaction.The spin and moments of the low-lying isomeric state in 73Zn suggest a strong onset of deformation at N = 43, while the progression towards 79Zn points to the stability of the Z = 28 and N = 50 shell gaps, supporting the magicity of 78N

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 manybody calculations5–8 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. Since the establishmentstatus: publishe

Evolution of nuclear structure in neutron-rich odd-Zn isotopes and isomers

Collinear laser spectroscopy was performed on Zn (Z=30) isotopes at ISOLDE, CERN. The study of hyperfine spectra of nuclei across the Zn isotopic chain, N=33–49, allowed the measurement of nuclear spins for the ground and isomeric states in odd-Aneutron-rich nuclei up to N=50. Exactly one long-lived (>10 ms) isomeric state has been established in each 69–79Zn isotope. The nuclear magnetic dipole moments and spectroscopic quadrupole moments are well reproduced by large-scale shell–model calculations in the f5pg9and fpg9d5model spaces, thus establishing the dominant term in their wave function. The magnetic moment of the intruder Iπ=1/2+isomer in 79Zn is reproduced only if the νs1/2orbital is added to the valence space, as realized in the recently developed PFSDG-U interaction. The spin and moments of the low-lying isomeric state in 73Zn suggest a strong onset of deformation at N=43, while the progression towards 79Zn points to the stability of the Z=28 and N=50 shell gaps, supporting the magicity of 78Ni