The accuracy of reaction theories used to extract properties of exotic nuclei from scattering experiments is often unknown or not quantified, but of utmost importance when, e.g., constraining the equation of state of asymmetric nuclear matter from observables as the neutron-skin thickness. In order to test the Glauber multiple-scattering model, the total interaction cross section of Image 1 on carbon targets was measured at initial beam energies of 400, 550, 650, 800, and 1000 MeV/nucleon. The measurements were performed during the first experiment of the newly constructed R3B (Reaction with Relativistic Radioactive Beams) experiment after the start of FAIR Phase-0 at the GSI/FAIR facility with beam energies of 400, 550, 650, 800, and 1000 MeV/nucleon. The combination of the large-acceptance dipole magnet GLAD and a newly designed and highly efficient Time-of-Flight detector enabled a precise transmission measurement with several target thicknesses for each initial beam energy with an experimental uncertainty of ±0.4%. A comparison with the Glauber model revealed a discrepancy of around 3.1% at higher beam energies, which will serve as a crucial baseline for the model-dependent uncertainty in future fragmentation experiments.

The ground-state decay width of the two-phonon J = 1-, 4742 keV state of 88Sr has been determined with the relative self-absorption method combined with a monoenergetic photon beam. This width is important to determine the decay transition strengths into the ground state and the one-phonon 2+1 and 3-1 levels which are required to verify the two-phonon character of the J = 1- state. The experiment was performed at the High Intensity gamma -ray Source (HI gamma S) using a novel experimental approach to adapt the relative self-absorption method to monoenergetic photon beams. The result for the ground-state decay width is, thus, independent of any calibration standard and confirms the two-phonon character of the 88Sr, Jr = 1-, 4742 keV state within an improved uncertainty.

. - We report on a new method to perform nuclear self-absorption measurements in combination with a monochromatic photon beam produced via laser Compton backscattering. We have used the method for two very different applications: The precision determination of the transition width of the first excited state in 12C to the ground state and to determine nuclear level densities up to the neutron separation energy in 88Sr. Both experiments serve as a proof of principle and are currently being analyzed. First preliminary results are presented.

Low energy fission of 234,235,236,238 U and 237,238 Np radioactive beams, provided by the GSI/FRS facility, has been studied using the R 3 B/SOFIA setup. The latter allows, on an event-by-event basis, to simultaneously identify, in terms of their mass and atomic numbers, the fissioning nucleus in coincidence with both fission fragments after prompt-neutron emission. This presentation reports on new results on elemental, isobaric and isotopic yields.

In the last decades, measurements of spallation, fragmentation and Coulex induced fission reactions in inverse kinematics have provided valuable data to accurately investigate the fission dynamics and nuclear structure at large deformations of a large variety of stable and non-stable heavy nuclei. To go a step further, we propose now to induce fission by the use of quasi-free (p,2p) scattering reactions in inverse kinematics, which allows us to reconstruct the excitation energy of the compound fissioning system by using the four-momenta of the two outgoing protons. Therefore, this new approach might permit to correlate the excitation energy with the charge and mass distributions of the fission fragments and with the fission probabilities, given for the first time direct access to the simultaneous measurement of the fission yield dependence on temperature and fission barrier heights of exotic heavy nuclei, respectively. The first experiment based on this methodology was realized recently at the GSI/FAIR facility and a detailed description of the experimental setup is given here.

Despite the recent experimental and theoretical progress in the investigation of the nuclear fission process, a complete description still represents a challenge in nuclear physics because it is a very complex dynamical process, whose description involves the coupling between intrinsic and collective degrees of freedom, as well as different quantum-mechanical phenomena. To improve on the existing data on nuclear fission, we produce fission reactions of heavy nuclei in inverse kinematics by using quasi-free (p,2p) scattering, which induce fission through particle-hole excitations that can range from few to ten's of MeV. The measurement of the four-momenta of the two outgoing protons allows to reconstruct the excitation energy of the fissioning compound nucleus and therefore to study the evolution of the fission yields with temperature. The realization of this kind of experiment requires a complex experimental setup, providing full isotopic identification of both fission fragments and an accurate measurement of the momenta of the two outgoing protons. This was realized recently at the GSI/FAIR facility and here some preliminary results are presented.

The Reactions with Relativistic Radioactive Beams (R3B) collaboration of the Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany, has constructed an experimental setup to perform fundamental studies of nuclear matter, using as a probe reactions with exotic nuclei at relativistic energies. Among the various detection systems, one of the most recent upgrades consists of the installation of a large area, around 2 m2, multi-gap Resistive Plate Chamber (RPC). The chamber is equipped with twelve 0.3 mm gaps and readout by 30 mm pitch strips, exhibiting a timing precision down to 50 ps and efficiencies above 98% for minimum ionizing particles in a previous characterization of the detector. The RPC was part of the setup of the FAIR Phase 0 experiment that focused on measuring for the first time, in spring 2022, nucleon-nucleon short-range correlations (SRC) inside an exotic nucleus (16C). The excellent timing precision of this detector will allow the measurement of the forward emitted proton momentum with a resolution of around 1%. In beam measurements show an RPC efficiency above 95% and a time precision better than 100 ps (including the contribution of a reference scintillator and the momentum spread of the particles) for forward emitted particles.

Low-energy investigations on rare ion beams are often limited by the available intensity and purity of the ion species in focus. Here, we present the first application of a technique that combines in-flight production at relativistic energies with subsequent secondary beam storage, accumulation and finally deceleration to the energy of interest. Using the FRS and ESR facilities at GSI, this scheme was pioneered to provide a secondary beam of ^118Te^52+ for the measurement of nuclear proton-capture at energies of 6 and 7 MeV/u. The technique provided stored beam intensities of about 10^6 ions at high purity and brilliance, representing a major step towards low-energy nuclear physics studies using rare ion beams.

The proton drip-line nucleus 17Ne is investigated experimentally in order to determine its two-proton halo character. A fully exclusive measurement of the 17Ne(p,2p)16F→15⁎O+p quasi-free one-proton knockout reaction has been performed at GSI at around 500 MeV/nucleon beam energy. All particles resulting from the scattering process have been detected. The relevant reconstructed quantities are the angles of the two protons scattered in quasi-elastic kinematics, the decay of 16F into 15O (including γ decays from excited states) and a proton, as well as the 15O+p relative-energy spectrum and the 16F momentum distributions. The latter two quantities allow an independent and consistent determination of the fractions of l=0 and l=2 motion of the valence protons in 17Ne. With a resulting relatively small l=0 component of only around 35(3)%, it is concluded that 17Ne exhibits a rather modest halo character only. The quantitative agreement of the two values deduced from the energy spectrum and the momentum distributions supports the theoretical treatment of the calculation of momentum distributions after quasi-free knockout reactions at high energies by taking into account distortions based on the Glauber theory. Moreover, the experimental data allow the separation of valence-proton knockout and knockout from the 15O core. The latter process contributes with 11.8(3.1) mb around 40% to the total proton-knockout cross section of 30.3(2.3) mb, which explains previously reported contradicting conclusions derived from inclusive cross sections.

We report on the first integration of novel magnetic microcalorimeter detectors (MMCs), developed within SPARC (Stored Particles Atomic Physics Research Collaboration), into the experimental environment of storage rings at GSI 6 6 GSI Helmholtzzentrum für Schwerionenforschung GmbH, Planckstraße 1, 64 291 Darmstadt., Darmstadt, namely at the electron cooler of CRYRING@ESR. Two of these detector systems were positioned at the 0° and 180° view ports of the cooler section to obtain high-resolution x-ray spectra originating from a stored beam of hydrogen-like uranium interacting with the cooler electrons. While previous test measurements with microcalorimeters at the accelerator facility of GSI were conducted in the mode of well-established stand-alone operation, for the present experiment we implemented several notable modifications to exploit the full potential of this type of detector for precision x-ray spectroscopy of stored heavy ions. Among these are a new readout system compatible with the multi branch system data acquisition platform of GSI, the synchronization of a quasi-continuous energy calibration with the operation cycle of the accelerator facility, as well as the first exploitation of the maXs detectors’ time resolution to apply coincidence conditions for the detection of photons and charge-changed ions. GSI Helmholtzzentrum für Schwerionenforschung GmbH, Planckstraße 1, 64 291 Darmstadt.

Background: Numerous studies of the ground-state decay of the pygmy dipole resonance (PDR) have been carried out in the past. However, data on the decay of the PDR to low-lying excited states is still very scarce due to limitations of the sensitivity to weak branching transitions of experimental setups. Purpose: We present a detailed examination of the low-energy dipole response of Te-128 and Te-130 below their neutron separation thresholds of 8.8 and 8.5 MeV, respectively. Methods: Photonuclear reactions with the subsequent gamma-ray spectroscopy of the decay channel with continuous-energy bremsstrahlung at varying endpoint energies and linearly polarized quasimonochromatic gamma-ray beams with energies ranging from 2.7 to 8.9 MeV in steps of roughly 250 keV were used for probing the decay behavior of the low-energy dipole response in Te-128 and Te-130. In addition, ((gamma) over right arrow, gamma ' gamma '') reactions were used to study the population of low-lying states of Te-128. Results: Spin-parity quantum numbers and reduced transition probabilities are determined for individual photo-excited states. The analysis of average decay properties for nuclear levels in narrow excitation-energy bins enable the extraction of photoabsorption cross sections, average branching ratios to the 2(1)(+) state, and the distinction between E1 and M1 transitions to the ground state and to the 2(1)(+) state accounting for resolved and unresolved transitions. Conclusions: Above 5 MeV, the experimental data are in reasonable agreement to calculations within the quasiparticle phonon model. The major fraction of the ground-state decay channel is due to E1 transitions, while less than 5-10% stem from M1 transitions. Furthermore, first direct experimental evidence is provided that the population of the 2(1)(+) state of Te-128 via primary gamma-ray transitions from excited states in the PDR region from 5 to 9 MeV is dominated by E1 transitions of 1(-) states.

The E2/M1 multipole mixing ratio of the 1(sc)(+) -> 2(1)(+) gamma-ray transition and therefore the F-vector E2 decay of the scissors mode of the shape-phase transitional nucleus Sm-152 have been measured with the nuclear resonance fluorescence method at the High-Intensity gamma-ray Source (HI gamma S). Furthermore, parity quantum numbers of several dipole-excited states have been remeasured, making use of the polarized gamma-ray beam at HI gamma S, and partially reassigned. The new data enable an unambiguous determination of the proton and neutron effective boson quadrupole charges within the proton-neutron interacting boson model. With the well-constrained parameter set, a new mixed-symmetry state is predicted.

The well-known spherical-deformed-transitional nucleus and potential 0 nu beta beta emitter Nd-150 and its daughter Sm-150 were investigated in nuclear resonance fluorescence experiments using quasimonoenergetic, linearly polarized gamma-ray beams. For both nuclei transitions from the 1(+) scissors mode to the 0(2)(+) and 2(2)(+) states were observed for the first time and their respective M1 transition strengths were determined. Through a systematic investigation, a sensitivity of these transition strengths to the three Majorana parameters of the interacting boson model-2 (IBM-2) was established. In combination with the novel experimental data, this poses strong constraints to the Majorana parameters in improved IBM-2 representations of both nuclei. A subsequent recalculation of the nuclear matrix elements (NMEs) for the Nd-150 -> Sm-150 0 nu beta beta decay in the IBM-2 with these improved representations results in M-IBM-2((0)nu beta beta) [0(1)(+)] = 3.35 for the NME for 0 nu beta beta decay into the ground state of Sm-150 and M-IBM-2((0)nu(beta beta)) [0(2)(+)] = 1.30 for 0 nu beta beta decay to its 0(2)(+) state.

NeuLAND (New Large-Area Neutron Detector) is the next-generation neutron detector for the (RB)-B-3 (Reactions with Relativistic Radioactive Beams) experiment at FAIR (Facility for Antiproton and Ion Research). NeuLAND detects neutrons with energies from 100 to 1000 MeV, featuring a high detection efficiency, a high spatial and time resolution, and a large multi-neutron reconstruction efficiency. This is achieved by a highly granular design of organic scintillators: 3000 individual submodules with a size of 5 x 5 x 250 cm(3) are arranged in 30 double planes with 100 submodules each, providing an active area of 250 x 250 cm(2) and a total depth of 3 m. The spatial resolution due to the granularity together with a time resolution of sigma(t) <= 150 ps ensures highresolution capabilities. In conjunction with calorimetric properties, a multi-neutron reconstruction efficiency of 50% to 70% for four-neutron events will be achieved, depending on both the emission scenario and the boundary conditions allowed for the reconstruction method. We present in this paper the final design of the detector as well as results from test measurements and simulations on which this design is based.

Background: Little data is available for the pygmy dipole resonance (PDR) in axially deformed nuclei. Photon-scattering experiments are complicated by high level densities in the PDR region and the small energy difference of transitions to the ground state and to excited states.Purpose: We report on an experimental study of the low-energy dipole strength distribution of the well-deformed nucleus $^{164}\mathrm{Dy}$ between 4.0--7.7 MeV.Methods: The low-lying photoresponse of $^{164}\mathrm{Dy}$ has been investigated using the method of nuclear resonance fluorescence using a quasimonochromatic linearly polarized $\ensuremath{\gamma}$-ray beam in the energy range of 4.0--7.7 MeV in steps of 0.2 MeV.Results: For excitation energies between 4 MeV and 5 MeV, sufficiently low level densities allow for the identification of individual states, including level energies, reduced transition widths and branching ratios. Energy-averaged mean decay branching ratios, mean population ratios and partial absorption cross sections were determined above 5 MeV up to the neutron-separation threshold at 7.7 MeV. A Lorentzian-shaped enhancement of the partial photo absorption cross section followed by decays back to the ground-state band is found at 6.10(5) MeV with a width of 0.77(23) MeV. A comparison with results from complementary measurements is performed using the framework of the statistical model.Conclusions: The experimental results for the mean population ratios deviate systematically from the statistical model simulation by 30(6)%. However, they are in agreement within one standard deviation of the simulation.

Background: Detailed information on the low-lying dipole response in atomic nuclei along isotonic or isotopic chains is well suited to systematically investigate the structure and evolution of the pygmy dipole resonance (PDR). Moreover, the dipole strength below and around the neutron separation energy S-n has impact on statistical model calculations for nucleosynthesis processes. Purpose: The photon strength function (PSF) of Rb-87, which is directly connected to the photoabsorption cross section, is a crucial input for statistical model calculations constraining the Maxwellian-averaged cross section (MACS) of the neutron capture of the unstable s-process branching-point nucleus Rb-86. Within this work, the photoabsorption cross section is investigated. Methods: The photoabsorption cross section of the N = 50 nucleus Rb-87 was determined from photon-scattering experiments via the nuclear resonance fluorescence (NRF) technique. Bremsstrahlung beams at the gamma ELBE facility in conjunction with monoenergetic photon beams at the HI gamma S facility were used to determine the integrated cross sections I-s of isolated states as well as the averaged cross section as function of the excitation energy. Decays to the ground state were disentangled from decays to first low-lying excited states. Statistical and experimental approaches for the gamma-decay properties at various excitation energies were applied. The linearly polarized photon beams at HI gamma S provide information on the ratio of electric and magnetic type of radiation. Results: Within this work, more than 200 ground-state decays and associated levels in Rb-87 were identified. Moreover, transitions below the sensitivity limit of the state-by-state analysis were taken into account via a statistical approach from the bremsstrahlung data as well as model-independently from the HI gamma S data. The photoabsorption cross sections at various excitation energies were determined. The dipole response between 6 and 10 MeV of Rb-87 is in agreement with assuming contributions of electric multipolarity, only. Conclusions: The photoabsorption cross section of Rb-87 does not contradict with the trend of decreasing E1 strength with increasing proton number along the N = 50 isotonic chain but might also be associated with a constant trend. The experimental gamma decay at various excitation energies of the HI gamma S data supports the statistical approach but does not provide a stringent proof due to the limited sensitivity in the decay channels. The additional E1 strength observed in the present experiments significantly enhances the MACSs compared only to recent microscopic HFB+QRPA (Hartree-Fock-Bogoliubov plus quasiparticle random-phase approximation) calculations using the D1M interaction. Moreover, theoretical estimations provided by the KADoNiS project could be significantly improved.

The electron capture process was studied for Xe$^{54+}$ colliding with H$_2$ molecules at the internal gas target of the ESR storage ring at GSI, Darmstadt. Cross section values for electron capture into excited projectile states were deduced from the observed emission cross section of Lyman radiation, being emitted by the hydrogen-like ions subsequent to the capture of a target electron. The ion beam energy range was varied between 5.5 MeV/u and 30.9 MeV/u by applying the deceleration mode of the ESR. Thus, electron capture data was recorded at the intermediate and in particular the low collision energy regime, well below the beam energy necessary to produce bare xenon ions. The obtained data is found to be in reasonable qualitative agreement with theoretical approaches, while a commonly applied empirical formula significantly overestimates the experimental findings.

Luminosity is a measure of the colliding frequency between beam and target and it is a crucial parameter for the measurement of absolute values, such as reaction cross sections. In this paper, we make use of experimental data from the ESR storage ring to demonstrate that the luminosity can be precisely determined by modelling the measured Rutherford scattering distribution. The obtained results are in good agreement with an independent measurement based on the x-ray normalization method. Our new method provides an alternative way to precisely measure the luminosity in low-energy stored-beam configurations. This can be of great value in particular in dedicated low-energy storage rings where established methods are difficult or impossible to apply.

The achievable acquisition rates of modern triggered nuclear physics experiments are heavily dependent on the readout software, in addition to the limits given by the utilized hardware. This paper presents an asynchronous readout scheme that significantly improves the livetime of an otherwise synchronous triggered Versa Module Eurocard Bus-based data acquisition system. A detailed performance analysis of this and other readout schemes, in terms of the basic data transfer operations, is described. The performance of the newly developed scheme as well as synchronous schemes on two systems has been measured. The measurements show excellent agreement with the detailed description. For the second system, which previously used a synchronous readout, the deadtime ratio is at a 20-kHz trigger request frequency reduced by 30% compared to the nearest contender, allowing 10% more events to be recorded in the same time. The interaction between the network and readout tasks for single-core processors is also investigated. A livetime ratio loss of a few percents can be observed, depending on the size of the data chunks given to the operating system kernel for network transfer. With appropriately chosen chunk size, the effect can be mitigated.

Background: The low-lying electric dipole strength provides insights into the parameters of the nuclear equation of state via its connection with the pygmy dipole resonance and nuclear neutron skin thickness. Purpose: The aim was to complement the systematic of the pygmy dipole resonance and first study its behavior across the N = 28 neutron shell closure. Methods: Photon-scattering cross sections of states of Cr-50,Cr-54 were measured up to an excitation energy of 9.7 MeV via the nuclear resonance fluorescence method using gamma-ray beams from bremsstrahlung and Compton backscattering. Results: Transitions strengths, spin and parity quantum number, and average branching ratios for 55 excited states, 44 of which were observed for the first time, were determined. The comparison between the total observed strengths of the isotopes Cr-50,Cr-52,Cr-54 shows a significant increase above the shell closure. Conclusions: The evolution of the pygmy dipole resonance is heavily influenced by the shell structure.