The rare-earth peak in the r-process abundance pattern depends sensitively on both the astrophysical conditions and subtle changes in nuclear structure in the region. This work takes an important step elucidating the nuclear structure and reducing the uncertainties in r-process calculations via precise atomic mass measurements at the JYFLTRAP double Penning trap. 158 Nd, 160 Pm, 162 Sm, and 164−166 Gd have been measured for the first time and the precisions for 156 Nd, 158 Pm, 162,163 Eu, 163 Gd, and 164 Tb have been improved considerably. Nuclear structure has been probed via twoneutron separation energies S2n and neutron pairing energy metrics Dn. The data do not support the existence of a subshell closure at N = 100. Neutron pairing has been found to be weaker than predicted by theoretical mass models. The impact on the calculated r-process abundances has been studied. Substantial changes resulting in a smoother abundance distribution and a better agreement with the solar r-process abundances are observed.

Collinear laser spectroscopy was performed on the nuclear ground states of the neutron-deficient isotopes (206,205,204)Fr. A new technique was developed to suppress hyperfine pumping in collinear laser spectroscopy of atoms. This involved high-frequency intensity modulation of narrow-linewidth laser light using fast-switching electro-optical modulators. The nuclear ground-state spins of (206,205,204)Fr were determined to be 3, 9/2, and 3, respectively. Both the changes in mean-squared charge radii and nuclear magnetic dipole moments indicate a departure from single-particle estimates.

A β-detected nuclear quadrupole resonance (NQR) spectrometer becomes a powerful tool to study changes in nuclear ground-state properties along isotopic chains when coupled to a laser excitation beamline to polarize the nuclei of interest. Recently, the β-NQR technique in a zero magnetic field has been applied for the first time to measure the ratio of static nuclear quadrupole moments of 8,9 Li, Q 9 /Q 8 = 0.966 75(9) denoted by Q 8 for 8 Li and Q 9 for 9 Li, respectively. This shows agreement with present literature values but with significantly improved precision. Based on the literature, the quadrupole moment for 8 Li has been re-evaluated to be |Q 8 | = 32.6(5) mb. From this, the quadrupole moment for 9 Li is calculated as |Q 9 | = 31.5(5) mb with the error being dominated by the error of Q 8 .

Collinear laser fluorescence spectroscopy has been performed on the ground and isomeric states of 204,206 Fr in order to determine their spins, nuclear moments, and changes in mean-squared charge radii. A new experimental technique has been developed as part of this work which much enhances the data collection rate while maintaining the high resolution. This has permitted the extension of this study to the two isomeric states in each nucleus. The investigation of nuclear g factors and mean-squared charge radii indicates that the neutron-deficient Fr isotopes lie in a transitional region from spherical towards more collective structures.