The weak binding and spatially extended neutron densities characteristic of drip-line nuclei give rise to a distinctive low-energy dipole response. The drip-line nucleus ^{8}He is the most neutron-rich bound nucleus with a mass-to-charge ratio of A/Z=4. We measure the dipole response of ^{8}He, including for the first time the four-neutron decay channel. A total dipole strength of ∑B(E1)(E^{*}<15  MeV)=0.95(16)e^{2} fm^{2} and a dipole polarizability of α_{D}=0.61(1)  fm^{3} are extracted from the differential Coulomb-excitation cross section and compared to state-of-the-art theoretical calculations employing coupled cluster and three-body approaches. We find that the dipole continuum is dominated, even at high excitation energies well above the 4n decay threshold, by two-neutron emission, pointing to a ^{6}He+2n structure of the excited dipole mode. No indication was found for a 4n final-state correlation, while pronounced nn and ^{6}He-n final-state correlations are apparent.

The spectrum of the exotic three-proton (3p) emitter ^17Na has been studied by detecting all in-flight decay products. Derived from the measured angular correlations ^14O+p+p+p, a resonant peak has been discovered at the 3p-decay energy of 2.24(^+0.17_-0.25) MeV, which likely corresponds to the ^17Na ground state. This decay energy value is significantly smaller than the previous experimental upper limit. Our measured ^14O-p correlations stemming from the ground state decay have been quantitatively described by a sequential 1p-2p emission from a ^17Na resonance via the intermediate ^16Ne ground state, which allowed to derive the upper limit of ^17Na ground-state width of 0.6 MeV. A dramatic systematic decrease in the mirror energy differences of mirror nuclei pairs has been observed at almost all 3p emitters with known proton separation energy (such as ^31K, ^20Al, and ^17Na), in sharp contrast to the behavior in less exotic nuclei. Such a lowering effect indicates a general trend in evolution of nuclear structure for light to medium mass nuclei beyond the proton drip line, which is often associated with strong isospin symmetry breaking.

The reaction mechanism of the quasi-free scattering (QFS) reaction 12C(p, 2p)11B is investigated in inverse and complete kinematics using a 12C beam at 400 MeV/nucleon impinging on a polyethylene (CH2) target. A complete set of kinematic observables characterizing the three-body final state is obtained through the exclusive reconstruction of the 11B recoil fragment and the two outgoing protons. For the first time, a systematic Treiman-Yang test is applied to inverse-kinematics (p, 2p) reactions with a heavy-ion beam, taking advantage of the large phase space covered by the experimental setup, particularly in non-coplanar kinematic configuration. This model-independent test confirms the predominance of the QFS reaction mechanism. The characteristic dependence of the Treiman-Yang angle on the azimuthal correlation of the outgoing protons, along with other kinematic signatures, provides further evidence for the single-step proton knockout process.

We report charge pickup reaction cross sections for 24 p-shell isotopes, including ^8,9Li, ^10-12Be, ^10,13-15B, ^12,14-19C and ^14,15,17-22N, measured at relativistic energies (approximately 900A MeV) on both hydrogen and carbon targets. For the first time, we reveal a universal rapid increase in the charge pickup cross sections of unstable projectiles with isospin asymmetry along several isotopic chains. The cross sections can be decoupled into distinct contributions from the mass number and isospin asymmetry of the projectile, highlighting the critical role of the latter, and can be formulated empirically.

The previously-unknown nucleus 20Al has been observed for the first time by detecting its in-flight decays. Tracking trajectories of all decay products with silicon micro-strip detectors allowed for a conclusion that 20Al is unbound with respect to three-proton (3p) emission. The 3p-decay energy of 20Al ground state has been determined to be 1.93(+0.11,-0.09) MeV through a detailed study of angular correlations of its decay products, 17Ne+p+p+p. This value is much smaller in comparison with the predictions inferred from the isospin symmetry by using the known energy of its mirror nucleus 20N, which indicates a possible mirror symmetry violation in the structure of 3p emitters. Such an isospin symmetry breaking is supported by the calculations of the continuum embedded theoretical frameworks, describing the observed 20Al ground state as an 1p s-wave state with a spin-parity of 1-, which contradicts to the spin-parity (2-) of the 20N ground state. The 20Al ground state decays by sequential 1p-2p emission via intermediate ground state of 19Mg, which is the first observed case of daughter two-proton radioactivity following 1p decay of the parent state.

The combined use of the inverse kinematics technique and the advanced detection setup R3B (Reactions with Relativistic Radioactive Beams) at GSI/FAIR provides unique opportunities to study the fission process. This approach provides access to the complete isotopic identification of the two fission fragments, the precise determination of their velocities and the measurement of the neutrons and gammas emitted in coincidence, for a wide range of unstable fissile nuclei. In addition, quasi-free NN scattering represents a surrogate reaction to induce fission, allowing the complete identification of the fissioning system in terms of isotopic composition and excitation energy. The manuscript describes the technical realisation of these experiments as well as the physics programme and some preliminary results.

Neutron-rich light isotopes offer a great tool to extend our current knowledge of nuclear physics. On the one hand, they are optimal systems for investigating nucleon-nucleon correlations. On the other hand, exotic nuclei are crucial when studying the reduction factor (ratio of experimental cross sections relative to theoretical predictions) found in some previous studies for single-nucleon knockout reactions. The conclusions about the dependence of this reduction on the ΔS of the projectile are varied, therefore having more data for extreme values of ΔS is fundamental. The (p,pX) knockout reactions studied with the R3B setup offer a unique opportunity for kinematically complete measurements using inverse kinematics. This work presents the experiment, explaining how this data could shed some light on investigations where there is still room for improvement.

Nuclear fission leads to the splitting of a nucleus into two fragments(1,2). Studying the distribution of the masses and charges of the fragments is essential for establishing the fission mechanisms and refining the theoretical models(3,4). It has value for our understanding of r-process nucleosynthesis(5,6), in which the fission of nuclei with extreme neutron-to-proton ratios is pivotal for determining astrophysical abundances and understanding the origin of the elements(7) and for energy applications(8,9). Although the asymmetric distribution of fragments is well understood for actinides (elements in the periodic table with atomic numbers from 89 to 103) based on shell effects(10), symmetric fission governs the scission process for lighter elements. However, unexpected asymmetric splits have been observed in neutron-deficient exotic nuclei(11), prompting extensive further investigations. Here we present measurements of the charge distributions of fission fragments for 100 exotic fissioning systems, 75 of which have never been measured, and establish a connection between the neutron-deficient sub-lead region and the well-understood actinide region. These new data comprehensively map the asymmetric fission island and provide clear evidence for the role played by the deformed Z = 36 proton shell of the light fragment in the fission of sub-lead nuclei. Our dataset will help constrain the fission models used to estimate the fission properties of nuclei with extreme neutron-to-proton ratios for which experimental data are unavailable.

The (RB)-B-3 (Reactions with Relativistic Radioactive Beams) experiment as a major instrument of the NUSTAR collaboration for the research facility FAIR in Darmstadt is designed for kinematically complete studies of reactions with high-energy radioactive beams. Part of the broad physics program of (RB)-B-3 is to constrain the asymmetry term in the nuclear equation-of-state and hence improve the description of highly asymmetric nuclear matter (e.g., in neutron stars). For a precise determination of the neutron-skin thickness - an observable which is directly correlated with the symmetry energy in theoretical calculations - by measuring absolute fragmentation cross sections, it is essential to quantify the uncertainty and challenge the reaction model under stable conditions. During the successful FAIR Phase-0 campaign of (RB)-B-3, we precisely measured the energy dependence of total interaction cross sections in C-12+C-12 collisions, for a direct comparison with calculations based on the eikonal reaction theory.

Previous studies have shown a reduction in cross sections relative to theoretical predictions for single-nucleon knockout reactions, with varying conclusions about the dependence of this reduction on the N/Z ratio of the projectile. The (p,pX) knockout reactions studied with the R3B setup offer a unique opportunity for kinematically complete measurements using inverse kinematics. This work focuses on the development of an algorithm for performing particle identification using the CALIFA detector, of vital importance for the study of knocked-out clusters such as deuterium.

We report on the observation of previously-unknown isotope ^21Al, the first unbound aluminum isotope located beyond the proton dripline. The ^21Al nucleus decays by one-proton (1p) emission, and its in-flight decays were detected by tracking trajectories of all decay products with micro-strip silicon detectors. The 1p-emission processes were studied by analyses of the measured angular correlations of decay products ^20Mg+p. The 1p-decay energies of ground and low-lying excited states of ^21Al, its mass excess and proton separation energy value S_p=-1.1(1) MeV were determined.

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.

A multi-shot target assembly and automatic alignment procedure for laser-plasma proton acceleration at high repetition rate are introduced. The assembly is based on a multi-target rotating wheel capable of hosting more than 5000 targets, mounted on a 3D motorized stage to allow rapid replenishment and alignment of the target material between laser irradiations. The automatic alignment procedure consists of a detailed mapping of the impact positions at the target surface prior to the irradiation that ensures stable operation of the target, which alongside the purpose-built design of the target wheel, enables operation at rates up to 10 Hz. Stable and continuous laser-driven proton acceleration at 10 Hz is demonstrated, with observed cut-off energy stability about 15%.

The unexplained disagreement in the dependence of spectroscopic factors (C2Sexp) on the binding energy obtained by nucleon knockout using different targets is still a puzzle that needs to be addressed. To find an explanation of this riddle through exclusive measurements using different targets. The exclusive measurements were performed by using a Ne17 beam with an energy of 500 MeV/u incident on C and CH2 targets. Through the standard theoretical approach, C2Sexp were derived from the analysis of the experimental data on proton ejection from the proton halo in Ne17 as well as from its core O15. For the C target, proton ejection from the proton halo gave C2Sexp about 37% smaller than for the H target. But when protons are ejected from the core of Ne17, C2Sexp are identical within statistical uncertainties. An explanation for the difference in C2Sexp could be the removal of both halo protons, a more important reaction pathway for the C target. The C2Sexp values obtained by analyzing the proton ejection from the core indicate that it is not affected by the interaction with the halo protons. Published by the American Physical Society 2024

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.

This work presents a systematic study of the properties (Light Output Non-Uniformity (LONU) and energy resolution) of two CsI(Tl) scintillation units over a span of almost three years, under adverse conditions of humidity and temperature. These two crystals are part of the CALIFA detector, a highly segmented calorimeter and spectrometer for γ rays and light-charged particles, that is placed surrounding the reaction target at Cave C, the experimental cave of the R3B (Reactions with Radioactive Relativistic Beams) collaboration at the GSI-FAIR facilities in Darmstadt, Germany. The findings obtained after the experiment indicate that there was no significant impact on the performance in terms of resolution and LONU. This suggests that the employed wrapping for light collection effectively serves as an excellent barrier against humidity. As a result, the crystal is preserved in a far better condition than initially anticipated.

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. The collected data were used to constrain dynamic and nuclear structure parameters of different de-excitation models, such as ABLA and GEF, but the data can also be used to constrain the parameterizations describing the pre-fragment properties after the nuclear collision, such as the angular momentum gained by the pre-fragment. In this work, the fissioning system yields are compared to calculations assuming different parameterizations for modeling the angular momentum gained by the compound nuclei. Our findings indicate that the parameterizations utilized by abrasion models clearly underestimate the angular momentum, resulting in the underestimation of the production of lighter fissioning systems.

Nuclear fission is a complex dynamical process, whose description involves the coupling between intrinsic and collective degrees of freedom, as well as different quantum-mechanical phenomena. For this reason, to this day it still lacks a satisfactory and complete microscopic description. In addition to the importance of describing fission itself, studies of the r-process in astrophysics depend on fission observables to constrain the theoretical models that explain the isotopic abundances in the Universe. To improve on the existing data, fission reactions of heavy nuclei in inverse kinematics are produced in quasi-free (p,2p) scattering reactions, which induce fission through particle-hole excitations that can range from few to tens of MeV. In order to study the evolution of the fission yields with temperature, the excitation energy of the fissioning system must be reconstructed, which is possible by measuring the four-momenta of the two outgoing protons. Performing 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 some of the results obtained for the charge distributions are presented in this work.

The experimental data collected during the S515 experiment performed by the R3B collaboration at GSI/FAIR represent a great opportunity to investigate nucleon knockout reactions of exotic nuclei in the region of Sn using complete kinematics measurements. These cross sections can be used in the future to investigate the quenching in the knockout of the minority species (neutrons or protons) in nuclei far from stability. Some of the arguments put forward are the underestimation of the knockout of deeply bound nucleons, final state interactions or the role of short-range correlations (SRC). Recently, several works based on inclusive measurements have shown that these SRCs could reduce the single nucleon knockout cross sections by around 50%, depending on the neutron excess (N/Z) of the initial projectile. The S515 data can help us to go further in this investigation because it allows to correlate the knockout cross sections of one, two or more nucleons with the number of protons and neutrons emitted from the target and which can be detected by the CALIFA and NeuLAND detectors, respectively, and perform complete kinematical studies on the nature of the event (SRC, evaporation, emission of clusters, final-state interactions...). Here the results obtained for the charge distribution of reaction residues are presented, which is one of the first steps of the still on-going analysis.