Isabelle Brandherm

High-Energy and Nuclear Physics research facilities around the world demand cutting-edge instruments dedicated to exploring the signatures of particles knocked out by collisions at ultra-relativistic energies. Each instrument is a class of its own, but shares underlying technologies proven to solve specific challenges. Polymer-based scintillating fibers (cross sections typically below 1 mm²) are sensitive to a large range of particle types and broad energy ranges and provide a fast response, fine spatial segmentation, and a low material budget, making them suitable for particle tracking, beam monitoring, and timing applications. Indeed, scintillating fibers can cover a large variety of shapes and sizes when assembled as ribbons, also allowing for multilayer designs. While most multilayer fiber detectors employ round-section fibers in staggered layers configuration, the square cross section permits regular arrangements with gapless fully packed ribbons and a quasi-uniform distribution of sensitive material. This work presents the manufacturing process developed at the Detector Laboratory of GSI Helmholtzzentrum für Schwerionenforschung (Germany) for manufacturing single- and multilayer ribbons made of scintillating square fibers. The complete production sequence is described, including fiber winding and positioning, bonding of layers, stacking and alignment of multilayer ribbons, integration of mechanical interfaces, machining and surface finishing of the optical couplings, and quality control procedures. Dedicated tooling was developed for each production stage to provide mechanical reproducibility and scalability. The process can be fully adapted to different fiber sizes, ribbon widths and lengths, and layer configurations, enabling the production of both small prototypes and large-format modules. This technology, already validated in operative instruments, is being deployed in a new generation of experiments for the international Facility for Antiproton and Ion Research (FAIR) research center.

Short-Lived Radionuclides (SLRs) with million-year lifetimes serve as chronometers of Early Solar System (ESS) formation and can reveal active nucleosynthesis in our Galaxy. Among the nuclides whose decay signatures are preserved in meteorites, the extinct radionuclide ⁹² Nb is one of the few confirmed proton-rich SLRs, and the ESS ⁹² Nb/ ⁹² Mo abundance ratio serves as a sensitive probe of proton-rich nucleosynthesis. However, the interpretation of this ratio is complicated by uncertainties in both nuclear reaction rates and the astrophysical environments. Because ⁹² Nb is shielded by the stable isobars ⁹² Zr and ⁹² Mo, it cannot be produced through β-decay chains. Instead, it must be synthesized through direct reactions in explosive supernova environments, where the photoneutron reaction on ⁹² Nb is a key regulator and currently dominates the uncertainty in the nuclear reaction networks producing ⁹² Nb. Direct measurements of this reaction are presently not feasible. Therefore, recommended values have relied on theoretical calculations. Here, we present the first experimental constraint on this reaction. This newly constrained reaction rate significantly increases the predicted ⁹² Nb abundance in relevant supernova environments, thereby shifting model predictions in the direction needed to ease the long-standing discrepancy in the ESS ⁹² Nb/ ⁹² Mo ratio by removing one of the dominant nuclear uncertainties in the ⁹² Nb production network.

This corrects the article DOI: 10.1103/PhysRevLett.133.232502.

The electric dipole strength distribution in Ni 58 between 6 and 20 MeV has been determined from proton inelastic scattering experiments at very forward angles at RCNP, Osaka. The experimental data are rather well reproduced by quasiparticle random-phase approximation calculations including vibration coupling, despite a mild dependence on the adopted Skyrme interaction. They allow an estimate of the experimentally inaccessible high-energy contribution above 20 MeV, leading to an electric dipole polarizability α D ( Ni 58 ) = 3.48 ( 31 ) fm 3 . This serves as a test case for recent extensions of coupled-cluster calculations with chiral effective field theory interactions to nuclei with two nucleons on top of a closed-shell system.

Dipole toroidal modes appear in many fields of physics. In nuclei, such a mode was predicted more than 50 years ago, but clear experimental evidence was lacking so far. Using a combination of high-resolution inelastic scattering experiments with photons, electrons, and protons, we identify for the first time candidates for toroidal dipole excitations in the nucleus ^{58}Ni and demonstrate that transverse electron scattering form factors represent a relevant experimental observable to prove their nature.

Background: Electric and magnetic dipole strengths in nuclei at excitation energies well below the giant resonance region are of interest for a variety of nuclear structure problems including a possible electric dipole toroidal mode or the quenching of spin-isospin flip modes.