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 theory framework to determine the atomic field shift and mass shift 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 coupled-cluster theory has been applied to determine mass shift 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 $^2$P$_{3/2}$ $\rightarrow$ 9s $^2$S$_{1/2}$) and 246.0-nm (5p $^2$P$_{1/2}$ $\rightarrow$ 8s $^2$S$_{1/2}$) 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.

https://iopscience.iop.org/article/10.1088/1367-2630/ab66dd/pdf

Analytic response relativistic coupled-cluster theory: the first application to indium isotope shifts

In this work, we extend two successful nuclear-structure methods, the valence-space and the no-core shell model, to new domains of applications.

We address key developments for a realistic implementation of the valence-space shell model to enhance its predictive power and allow for a description of arbitrary nuclei, ranging from the valley of stability to the neutron-deficient or neutron-rich extremes of the Segre chart.
One essential step is the capability to deal with valence spaces that comprise more than a single major shell.
We propose an importance-truncation scheme for the valence-space shell model based on a physics-driven and adaptive truncation that, in combination with refined extrapolation techniques, provides an efficient and accurate tool for the description of nuclei in large-scale model spaces.
Additionally, we explore effective valence-space Hamiltonians derived from chiral interactions in the in-medium similarity renormalization group.
These interactions are rooted in quantum chromodynamics and provide an excellent framework to describe nuclear properties from first principles.
Using these interactions, we demonstrate the reliability of the approach in single-shell valence spaces; however, difficulties persist with the construction of effective Hamiltonians for multi-shell valence spaces.
While an ab initio description of nuclei in the framework of the importance-truncated valence-space shell model is not yet feasible, we study ground and first excited states of neutron-deficient tin isotopes in the gds valence space based on effective Hamiltonians that are constrained by few-body data only.
Our results highlight the need for a more rigorous and systematic approach for the construction of nuclear interactions.

Moreover, we present an ab initio approach for the description of collective excitations and transition-strength distributions by combining the importance-truncated no-core shell model with the Lanczos strength-function method.
Due to its computational efficiency, this method can be applied to all nuclei that are feasible in the no-core shell model.
It provides access to the full energy range from low-lying excitations to the giant-resonance region and beyond in a unified and consistent framework, including a complete description of fragmentation and fine structure.
The method relies solely on the basis truncation, and we demonstrate convergence of the strength distributions with the truncation parameter.
Starting from chiral effective-field-theory interactions, we explore the electric monopole, dipole, and quadrupole response of oxygen, carbon, and helium isotopes.
We focus on the emergence and evolution of pygmy and giant resonances, as well as the systematics of dipole polarizabilities throughout the isotopic chains.
Furthermore, we study transition densities of prominent transitions in the distributions, which provide valuable insights in their nature.
The results underline the importance of collective modes for constraining nuclear interactions.
In addition, we elaborate on the relation with approximate methods, such as the random-phase approximation, and shed new light on their deficiencies.

Nuclear Spectra and Strength Distributions from Importance-Truncated Configuration-Interaction Methods

Strongly correlated many-body systems often display the emergence of simple patterns and regular behaviour of their global properties. Phenomena such as clusterization, collective motion and appearance of shell structures are commonly observed across different size, time, and energy scales in our universe. Although at the microscopic level their individual parts are described by complex interactions, the collective behaviour of these systems can exhibit strikingly regular patterns. This contribution provides an overview of the experimental signatures that are commonly used to identify the emergence of shell structures and collective phenomena in distinct physical systems. Examples in macroscopic systems are presented alongside features observed in atomic nuclei. The discussion is focused on the experimental trends observed for exotic nuclei in the vicinity of nuclear closed-shells, and the new challenges that recent experiments have posed in our understanding of emergent phenomena in nuclei.

/pdf/emergence-of-simple-patterns-in-many-body-systems-from-fofj2adknr.pdf

Emergence of simple patterns in many-body systems: from macroscopic objects to the atomic nucleus

A gas-filled linear Paul trap for the Collinear Resonance Ionisation Spectroscopy (CRIS) experiment at ISOLDE, CERN is currently under development. The trap is designed to accept beam from both ISOLDE target stations and the CRIS stable ion source. The motivation for the project along with the current design, simulations and future plans, will be outlined.

/pdf/a-compact-linear-paul-trap-cooler-buncher-for-cris-49u638cmjj.pdf

A compact linear Paul trap cooler buncher for CRIS

At the beginning of long shutdown 1, three collinear laser spectroscopy experiments using the COLLAPS setup remained open. IS519 (Zn) has yet to be scheduled, IS508 (Mn) was able to take 11 of the 18 shifts approved and IS529 (Ca) successfully completed all measurements for which shifts were allocated. In this document we demonstrate that the physics cases originally endorsed by the INTC remain significant and that substantial technical developments have been undertaken in order to fully address the remaining unmeasured isotopes.

Status Report to the ISOLDE and Neutron Time-of-Flight Committee

/pdf/laser-spectroscopy-of-exotic-indium-z-49-isotopes-k5dssvvvys.pdf

Laser Spectroscopy of exotic indium (Z = 49) isotopes: Approaching the N = 50 and N = 82 neutron numbers

/pdf/laser-spectroscopy-of-neutron-deficient-sn-isotopes-40nrf7oprk.pdf

Ronald Fernando

Papers

Laser Spectroscopy of exotic indium (Z = 49) isotopes: Approaching the N = 50 and N = 82 neutron numbers

Laser spectroscopy of neutron-deficient Sn isotopes

Towards laser spectroscopy of exotic fluorine isotopes

Collinear Laser Spectroscopy on exotic Ca isotopes towards new magic numbers N=32 and N=34