In this first period of NSHAPE, the focus has been on preparing the experimental campaign, technical developments, and initial data collection.
At KU Leuven, a new laser laboratory is under construction for the development of ionisation schemes for laser spectroscopy. This laboratory should enter full operation in the summer of 2025.
At CERN ISOLDE, tests have been performed to demonstrate the feasibility of the study of neutron-deficient lutetium isotopes with the PI-LIST device and a proposal was subsequently accepted to perform that study.
Meanwhile, the analysis of the data collected on the neutron-rich polonium and actinium isotopes with the PI-LIST is near completion. Those results have been presented at the International Nuclear Physics Conference 2025 and the preparation of publications of those results are in preparation.
At GANIL, the commissioning of the facility is facing some delays. To mitigate the impact on the NSHAPE programme, some initial measurements have been proposed at GSI in Germany, using the SHIP velocity filter, to investigate the most neutron-deficient lutetium isotopes, beyond what can be reached at ISOLDE. The beam time is planned for 2026.
At PSI, test data sets have been collected for muonic x-ray spectroscopy on the naturally available La-139, Th-232, and U-238 to demonstrate the feasibility of study more exotic isotopes of those elements. Furthermore, a full data set has been collected with natural and enriched lutetium, to complete the study of Lu-175,176. Combined with the laser spectroscopy data that should be collected at CERN ISOLDE and GSI, this would offer a comprehensive view of this isotopic chain.
Meanwhile, extensive technical developments are ongoing to support the muonic x-ray spectroscopy programme: a systematic study of target production techniques has demonstrated that implanted beams, as obtained from mass separation, are directly applicable in muonic x-ray spectroscopy experiments; this would enable the direct use of target prepared for NSHAPE with that technique. Moreover, development work has been performed to achieve the efficient mass separation of lanthanum isotopes, especially to produce a high-purity La-138 samples for the upcoming campaign. Monte Carlo simulations have been performed to demonstrate the improvement that can be achieved with high-purity germanium clover detectors instead of the current standard detectors used at PSI (BEGe, SEGe, REGe); this study has motivated to bring the ISOLDE Decay Station array to PSI for the 2026 campaign, to be complemented by 2 new detectors acquired from NSHAPE.
Finally, the full analysis pipeline for the determination of absolute charge radii from muonic x-ray spectroscopy has been established, using the somewhat simpler case of Cl-35,3y and K-39,40,41. This paves the way for the full analysis of the isotopes of interest to NSHAPE, while also helping identify the challenges that are faced by the theory groups.
