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Differential cross sections for elastic $p\text{\ensuremath{-}}^{6}\mathrm{He}$ and $p\text{\ensuremath{-}}^{8}\mathrm{He}$ scattering, measured in inverse kinematics at high momentum transfer up to the first diffraction minimum and at projectile energies around 700 MeV/u at GSI Darmstadt, are analyzed applying the sum-of-Gaussians (SOG) method based on the Glauber multiple-scattering theory. The rms point matter radii of $^{6}\mathrm{He}$ and $^{8}\mathrm{He}$ are deduced to be 2.29(6) fm and 2.53(7) fm, respectively, in close agreement with those from former analyses using phenomenological parametrizations for describing the matter distributions. With the aid of the measurement at high momentum transfer, the overall radial density distributions of $^{6}\mathrm{He}$ and $^{8}\mathrm{He}$ are precisely deduced using the SOG method, in particular at small radii. A pronounced core rearrangement by adding the valence neutrons to an $\ensuremath{\alpha}$-like core to form $^{6}\mathrm{He}$ and $^{8}\mathrm{He}$ is elucidated, and briefly discussed.

Mass measurements of the $^{69}$As, $^{70,71}$Se and $^{71}$Br isotopes, produced via fragmentation of a $^{124}$Xe primary beam at the FRS at GSI, have been performed with the multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS) of the FRS Ion Catcher with an unprecedented mass resolving power of almost 1,000,000. For the $^{69}$As isotope, this is the first direct mass measurement. A mass uncertainty of 22 keV was achieved with only 10 events. For the $^{70}$Se isotope, a mass uncertainty of 2.6 keV was obtained, corresponding to a relative accuracy of $\delta$m/m = 4.0$\times 10^{-8}$, with less than 500 events. The masses of the $^{71}$Se and $^{71}$Br isotopes were measured with an uncertainty of 23 and 16 keV, respectively. Our results for the $^{70,71}$Se and $^{71}$Br isotopes agree with the 2016 Atomic Mass Evaluation, and our result for the $^{69}$As isotope resolves the discrepancy between previous indirect measurements. We measured also the mass of $^{14}$N$^{15}$N$^{40}$Ar (A=69) with a relative accuracy of $\delta$m/m = 1.7$\times 10^{-8}$, the highest yet achieved with a MR-TOF-MS. Our results show that the measured restrengthening of the proton-neutron interaction ($\delta$V$_{pn}$) for odd-odd nuclei at the N=Z line above Z=29 (recently extended to Z=37) is hardly evident at N-Z=2, and not evident at N-Z=4. Nevertheless, detailed structure of $\delta$V$_{pn}$ along the N-Z=2 and N-Z=4 lines, confirmed by our mass measurements, may provide a hint regarding the ongoing $\approx$500 keV discrepancy in the mass value of the $^{70}$Br isotope, which prevents including it in the world average of ${Ft}$-value for superallowed 0$^+\rightarrow$ 0$^+$ $\beta$ decays. The reported work sets the stage for mass measurements with the FRS Ion Catcher of nuclei at and beyond the N=Z line in the same region of the nuclear chart, including the $^{70}$Br isotope., Comment: 11 pages, 4 figures, accepted for publication at Physical Review C

This work was supported in part by the Helmholtz International Center for FAIR (HIC for FAIR), the Helmholtz Association (grant IK-RU-002), the Russian Ministry of Education and Science (grant No. NSh- 932.2014.2), the Russian Science Foundation (grant No. 17-12-01367), the Polish National Science Center (Contract No. UMO-2011/01/B/ST2/01943), the Polish Ministry of Science and Higher Education (Grant No. 0079/DIA/2014/43,Grant Diamentowy), the Helmholtz- CAS Joint Research Group (grant HCJRG-108), the FPA2009-08848 contract (MICINN, Spain), the Justus- Liebig-Universit¨at Giesen (JLU) and GSI under the JLUGSI strategic Helmholtz partnership agreement. This article is a part of PhD thesis of X.-D. Xu. The authors acknowledge the help of D. Kostyleva in the preparation of the manuscript.

A novel method for measuring nuclear reactions in inverse kinematics with stored ion beams was successfully used to extract the nuclear-matter radius of $^{58}\mathrm{Ni}$. The experiment was performed at the experimental heavy-ion storage ring at the GSI facility using a stored $^{58}\mathrm{Ni}$ beam at energies of 100 and 150 MeV/u and an internal helium gas-jet target. Elastically scattered $\ensuremath{\alpha}$-recoils at low momentum transfers were measured with an in-ring detector system compatible with ultrahigh vacuum. Experimental angular distributions were fitted using density-dependent optical model potentials within the eikonal approximation. This permitted the extraction of the point-matter root-mean-square radius of $^{58}\mathrm{Ni}$ with an average value of 3.70(7) fm. Results from this work are in good agreement with several experiments performed in the past in normal kinematics. This pioneering experiment demonstrates a major breakthrough towards future investigations with far-from-stability stored beams using the present technique.

The $\ensuremath{\beta}$ decay of $^{31}\mathrm{Ar}$, produced by fragmentation of an $^{36}\mathrm{Ar}$ beam at 880 MeV/nucleon, was investigated. Identified ions of $^{31}\mathrm{Ar}$ were stopped in a gaseous time projection chamber with optical readout allowing us to record decay events with emission of protons. In addition to $\ensuremath{\beta}$-delayed emission of one and two protons we clearly observed the $\ensuremath{\beta}$-delayed three-proton branch. The branching ratio for this channel in $^{31}\mathrm{Ar}$ is found to be $0.07\ifmmode\pm\else\textpm\fi{}0.02$%.

Previously unknown states in ${}^{18}$Na and ${}^{19}$Mg have been studied by measuring the trajectories of their decay products with microstrip detectors. Analyzing angular correlations of the fragments provided information on decay energies and widths of the parent states. The ground state of ${}^{18}$Na has been detected and its one-proton decay energy of 1.23(15) MeV determined. Four previously unknown states in ${}^{19}$Mg at 2.1, 2.9, 3.6, and 5.2 MeV have been observed. The competition between simultaneous and sequential two-proton emission of states in ${}^{19}$Mg is discussed, and the conclusion of a direct mechanism of $2p$ radioactivity of the ${}^{19}$Mg ground state is confirmed.

A powerful method of investigating proton-unbound nuclear states by tracking their decay products in flight is discussed in detail. To verify the method, four known levels in 15 F , 16 Ne , and 19 Na were investigated by measuring the angular correlations between protons and the respective heavy-ion fragments stemming from the precursor decays in flight. The parent nuclei of interest were produced in nuclear reactions of one-neutron removal from 17 Ne and 20 Mg projectiles at energies of 410–450 A MeV. The trajectories of the respective decay products, 14 O + p + p and 18 Ne + p + p, were measured by applying a tracking technique with microstrip detectors. These data were used to reconstruct the angular correlations of the fragments, which provided information on energies and widths of the parent states. In addition for reproducing properties of known states, evidence for hitherto unknown excited states in 15 F and 16 Ne was found. This tracking technique has an advantage in studies of exotic nuclei beyond the proton drip line measuring the resonance energies and widths with a high precision although by using low-intensity beams and very thick targets.

The $^{7}\mathrm{H}$ and $^{6}\mathrm{H}$ nuclear systems were investigated via transfer reactions with a $^{8}\mathrm{He}$ beam at $15.4A$ MeV impinging in a $^{12}\mathrm{C}$ target. The experimental setup allowed a complete reconstruction of the reaction kinematics with the MAYA gas detector, based on the active-target concept, where the carbon atoms of the filling isobutane played also the role of reaction target. The $^{7}\mathrm{H}$ resonance was observed at $0.{57}_{\ensuremath{-}0.21}^{+0.42}$ MeV above the ${}^{3}\mathrm{H}+4n$ threshold with a width of $0.{09}_{\ensuremath{-}0.06}^{+0.94}$ MeV. The $^{6}\mathrm{H}$ system was formed at $2.{91}_{\ensuremath{-}0.95}^{+0.85}$ MeV with a resonance width of $1.{52}_{\ensuremath{-}0.35}^{+1.77}$ MeV. These results show the availability of nuclear structure information well outside the bounding limits, resulting in an extraordinary input to improve the present models and understanding of nuclear matter.

Proton-proton correlations were observed for the two-proton decays of the ground states of {sup 19}Mg and {sup 16}Ne. The trajectories of the respective decay products, {sup 17}Ne+p+p and {sup 14}O+p+p, were measured by using a tracking technique with microstrip detectors. These data were used to reconstruct the angular correlations of fragments projected on planes transverse to the precursor momenta. The measured three-particle correlations reflect a genuine three-body decay mechanism and allowed us to obtain spectroscopic information on the precursors with valence protons in the sd shell.