[en] First results are reported on the momentum distribution after one-neutron removal from ²⁴O at 920 MeV/u. The investigated isotopes were produced by projectile fragmentation of a 1 GeV/u ⁴⁸Ca beam in a beryllium production target placed at the entrance of the FRagment Separator (FRS). They were separated and identified in-flight at the mid-focal plane of the separator, where a carbon reaction target was placed. Due to the high resolution of the FRS, operated in dispersion matched-mode, precise momentum measurements of secondary fragments could be performed. The secondary fragments produced in the C target were detected at the final achromatic focal plane of the FRS thus providing the measurements independently of the large momentum spread of the primary fragments. The ²³O momentum distribution in the projectile rest frame and the one-neutron removal cross section can be well explained by using an eikonal model with a nearly pure 2s_1/2 occupation probability. This large s-wave probability indicates a spherical shell closure at N=16, thereby experimentally confirming earlier suggestions that ²⁴O is a new doubly magic nucleus.

[en] Measurements of momentum distributions after one neutron removal and interaction cross sections of Mg and Al nuclei in the island of inversion N=20 have been performed with the FRagment Separator (FRS) at GSI. The nuclear structure of isotopes in this region is interesting because of the observed breakdown of the N=20 shell closure for Mg isotopes. The investigated isotopes, among them ^33,34,35Mg and ³⁴Al, were produced by projectile fragmentation of a 1 GeV/u ⁴⁸Ca beam in a Be production target placed at the entrance of the FRS. They were separated and identified in flight up to the mid-focal plane of the separator, where the interaction target (C or CH₂) was located. Due to the high resolution of the achromatic mode of the FRS, precise momentum measurements of the produced fragments can be performed independently of the large momentum spread due to the reactions in the target. The experiment will provide information about the orbital angular momentum of the knocked out neutron, and thus about the single particle orbitals of the ground state of the studied nuclei. Details of the experiment and the data analysis results are presented

[en] Evolution of magic numbers in neutron-rich nuclei is one of the hot topics in contemporary nuclear structure physics. At RIB in-flight facilities worldwide it was possible to reach the drip line for oxygen isotopes including the access of 2^4O and its neighboring region by fragmentation of stable Ar and Ca beams. However the available spectroscopic information is still very limited. The access to this region of the nuclear chart has determined the existence of a new shell closure at N=16, as it was pointed out through the systematical trends on one-neutron separation energy [1]. The appearance of the N=16 shell gap in the O isotopes has been suggested due to an upward shift in energy of the d_3/2 neutron orbital as an effect of the (σ-σ) (τ-τ) interaction [2]. It has been supported experimentally by in-beam gamma spectroscopy for 2^3,24O [3] and invariant mass spectroscopy [4]. Direct reactions performed on the 2^3O nucleus, via nuclear and electromagnetic probes, have assigned a spin 1/2⁺ to the 2^3O ground state [5]. To establish 2^4O as a new doubly magic nucleus spectroscopic information are required. We report on first direct measurements of the spectroscopic factor of the ground state of 2^4O. The experiment was performed at the FRS, GSI using a single neutron removal reaction at 920 MeV/u. The large s-wave probability of the removed neutron shows the presence of a spherical shell closure, in good agreement with shell model calculations.(author)

[en] Time Projection Chambers with C-pads and integrated delay line readout were developed as position sensitive detectors for the Fragment separator at GSI Darmstadt. The main advantages of TPCs are a small amount of matter in the sensitive volume, high spatial resolution, and high tracking efficiency. Working parameters in experimental conditions are presented. Internal spatial resolutions of σ_x=88μm and σ_y=38μm were achieved. The tracking efficiency dependence on ion beam intensity was studied with ²³⁸U beam at 1 GeV/u energy. Efficiency of more than 99% was achieved up to 40 kHz and over 90% for 250 kHz ²³⁸U beam intensity. Different kinds of ions from proton to uranium were measured in many experiments and confirmed the result obtained.

[en] Excited states in ⁹⁶Ag were populated in fragmentation of an 850-MeV/u ¹²⁴Xe beam on a 4-g/cm² Be target. Three new high-spin isomers were identified and the structure of the populated states was investigated. The level scheme of ⁹⁶Ag was established, and a spin parity of (13^-), (15⁺), and (19⁺) was assigned to the new isomeric states. Shell-model calculations were performed in various model spaces, including πν(p_1/2,g_9/2,f_5/2,p_3/2) and the large-scale shell-model space πν(gds), to account for the observed parity changing M2 and E3 transitions from the (13^-) isomer and the E2 and E4 transitions from the (19⁺) core-excited isomer, respectively. The calculated level schemes and reduced transition strengths are found to be in very good agreement with the experiment.

[en] The most remote isotope from the proton drip line (by 4 atomic mass units) has been observed: ³¹K. It is unbound with respect to three-proton (3p) emission, and its decays have been detected in flight by measuring the trajectories of all decay products using microstrip detectors. The 3p emission processes have been studied by the means of angular correlations of ²⁸S + 3p and the respective decay vertices. The energies of the previously unknown ground and excited states of ³¹K have been determined. This provides its 3p separation energy value S³p of -4.6(2) MeV. Upper half-life limits of 10 ps of the observed ³¹K states have been derived from distributions of the measured decay vertices. (authors)

[en] A RISING experiment with an aim to study exotic Cd nuclei was carried out at GSI-FRS facility. Some preliminary results from this experiment are presented here. In particular, the β decay of ⁹⁶Cd to ⁹⁶Ag revealed the existence of a high spin isomer predicted a few decades ago. In this context, the structures of both these nuclei are discussed. Shell model calculations using the Gross-Frenkel interaction are used to interpret the results.

[en] An open problem in Nuclear Astrophysics concerns the understanding of electron-screening effects on nuclear reaction rates at stellar energies. In this framework, we have proposed to investigate the influence of the electron cloud on α-decay by measuring Q-values and α-decay half-lives of fully stripped, H-like and He-like ions. These kinds of measurements have been feasible just recently for highly-charged radioactive nuclides by fragmentation of ²³⁸U at relativistic energies at the FRS-ESR facility at GSI. In this way it is possible to produce, efficiently separate and store highly-charged α-emitters. Candidates for the proposed investigation were carefully selected and will be studied by using the Schottky Mass Spectroscopy technique. In order to establish a solid reference data set, lifetimes and Q_α-value measurements of the corresponding neutrals have been performed directly at the FRS, by implanting the separated ions into an active Silicon stopper.

[en] A second γ-decaying high-spin isomeric state, with a half-life of 197(22)ns, has been identified in the N=Z+2 nuclide ⁹⁴Pd as part of a stopped-beam Rare Isotope Spectroscopic INvestigation at GSI (RISING) experiment. Weisskopf estimates were used to establish a tentative spin/parity of 19^-, corresponding to the maximum possible spin of a negative parity state in the restricted (p_1/2, g_9/2) model space of empirical shell model calculations. The reproduction of the E3 decay properties of the isomer required an extension of the model space to include the f_5/2 and p_3/2 orbitals using the CD-Bonn potential. This is the first time that such an extension has been required for a high-spin isomer in the vicinity of ¹⁰⁰Sn and reveals the importance of such orbits for understanding the decay properties of high-spin isomers in this region. However, despite the need for the extended model space for the E3 decay, the dominant configuration for the 19^- state remains (πp_1/2^-1g_9/2^-3)₁₁ x (νg_9/2^-2)₈. The half-life of the known, 14⁺, isomer was remeasured and yielded a value of 499(13) ns.

[en] Precision experiments with relativistic fragments separated in-flight require special experimental methods to overcome the inherent large emittance from the creation in nuclear reactions and atomic interactions in matter. At GSI relativistic exotic nuclei have been produced via uranium projectile fragmentation and fission and investigated with the in- flight separator FRS directly, or in combination with either the storage-cooler ring ESR or the FRS Ion Catcher. 1000 A*MeV "2"3"8U ions were used to create 60 new neutron-rich isotopes separated and identified with the FRS to measure their production cross sections. In another experimental campaign the fragments were separated in flight and injected into the storage-cooler ring ESR for accurate mass and lifetime measurements. In these experiments we have obtained accurate new mass values analyzed via a novel method which has reduced the systematic errors for both Schottky Mass Spectrometry (SMS) and for Isochronous Mass Spectrometry (IMS). Pioneering experiments have been carried out with the FRS Ion Catcher consisting of 3 experimental components, the dispersive magnetic system of the FRS with a monoenergetic and a homogeneous degrader, a cryogenic stopping cell filled with pure helium and a multiple-reflection time-of flight mass separator. The FRS Ion Catcher enables high precision spectroscopy experiments with eV to keV exotic nuclides. Results from these different FRS experiments are presented in this overview together with prospects for the next-generation facility Super-FRS. The novel features of the Super-FRS compared with the present FRS will be discussed in addition. (authors)