Ruben de Groote

We present two newly constructed experimental setups - REBEL (Resonant Excitation of Beams with Electromagnetic fields and Lasers) and STRIPE (Stopping and Trapping of Radioactive Isotopes for Precision Experiments) - integrated into a single offline beamline at KU Leuven. REBEL is designed for collinear laser spectroscopy of ion bunches following isobaric separation with a multireflection time-of-flight mass spectrometer, enabling high-sensitivity measurements of mass-selected fast-ion beams. In contrast, STRIPE focuses on the deceleration, trapping, and laser cooling of ions in a segmented linear Paul trap, optimized for long interrogation times and precision spectroscopy. The shared infrastructure features stable high-voltage operation ($<10$ ppm), modular vacuum sections, and a fast-beam switchyard to route ions to either experiment. Initial results include a mass-resolving power of $R \approx 12900$ in REBEL and successful ion trapping and laser cooling of ions with a kinetic energy of 10 keV in STRIPE, with improved performance achieved using a frequency-modulated cooling laser. This dual-system platform enables the development and benchmarking of advanced spectroscopy and trapping techniques and is compatible with future operation at radioactive ion beam facilities.

High-precision mass measurements of exotic $^{95-97}$Ag isotopes close to the $N = Z$ line have been conducted with the JYFLTRAP double Penning trap mass spectrometer, with the silver ions produced using the recently commissioned inductively-heated hot cavity catcher laser ion source at the Ion Guide Isotope Separator On-Line facility. The atomic mass of $^{95}$Ag was directly determined for the first time. In addition, the atomic masses of $β$-decaying 2$^+$ and 8$^+$ states in $^{96}$Ag have been identified and measured for the first time, and the precision of the $^{97}$Ag mass has been improved. The newly measured masses, with a precision of $\approx$ 1 keV/c$^2$, have been used to investigate the $N =$ 50 neutron shell closure confirming it to be robust. Empirical shell-gap and pairing energies determined with the new ground-state mass data are compared with the state-of-the-art \textit{ab initio} calculations with various chiral effective field theory Hamiltonians. The precise determination of the excitation energy of the $^{96m}$Ag isomer in particular serves as a benchmark for \textit{ab initio} predictions of nuclear properties beyond the ground state, specifically for odd-odd nuclei situated in proximity to the proton dripline below $^{100}$Sn. In addition, density functional theory (DFT) calculations and configuration-interaction shell-model (CISM) calculations are compared with the experimental results. All theoretical approaches face challenges to reproduce the trend of nuclear ground-state properties in the silver isotopic chain across the $N =$50 neutron shell and toward the proton drip-line.

RAPTOR, Resonance ionization spectroscopy And Purification Traps for Optimized spectRoscopy, is a new collinear resonance ionization spectroscopy device constructed at the Ion Guide Isotope Separator On-Line (IGISOL) facility at the University of Jyväskylä, Finland. By operating at beam energies of under 10 keV, the footprint of the experiment is reduced compared to more traditional collinear laser spectroscopy beamlines. In addition, RAPTOR is coupled to the JYFLTRAP Penning trap mass spectrometer, opening a window to laser-assisted nuclear-state selective purification, serving not only the mass measurement program, but also supporting post-trap decay spectroscopy experiments. Finally, the low-energy ion beams used for RAPTOR will enable high-precision laser-radiofrequency double-resonance experiments, resulting in spectroscopy with linewidths below 1 MHz. In this contribution, the technical layout of RAPTOR and a selection of ion-beam optical simulations for the device are presented, along with a discussion of the current status of the commissioning experiments.