Search

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.

Spectroscopic investigations performed at the neutron drip line in case of sd shell nuclei have recently shown the existence of the new magic numbers Z = 8 and N = 14,16. Predictions within the nuclear shell model calculations for the 23,24O ground state have been confirmed measuring their neutron occupancy in breakup reactions performed by using the inflight radioactive ion beams produced at the Fragment Separator FRS of GSI. Some perspectives of studying the evolution of magic numbers in this region of light exotic nuclei are given.

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 Qα‐value measurements of the corresponding neutrals have been performed directly at the FRS, by implanting the separated ions into an active Silicon stopper.

A concentration of dipole strength at energies below the giant dipole resonance was observed in neutron-rich nuclei around Sn-132 in an experiment using the FRS-LAND setup. This so-called "pygmy" dipole strength can be related to the parameters of the symmetry energy and to the neutron skin thickness on the grounds of a relativistic quasiparticle random-phase approximation. Using this ansatz and the experimental findings for Sn-130 and 132 Sri, we derive a value of the symmetry energy pressure of (p) over bar (0) = 2.2 +/- 0.5 MeV/fm(3). Neutron skin thicknesses of R-n-R-p = 0.23 +/- 0.03 fm and 0.24 +/- 0.03 fm for Sn-130 and Sn-132, respectively, have been determined. Preliminary results on Ni-68 from a similar experiment using an improved setup indicate an enhanced cross section at low energies, while the results for Ni-58 are in accordance with results from photoabsorption measurements.

Advanced nuclear structure models predict the presence of the shell closures N = 14, 16 in neutron‐rich O isotopes rather than N = 20. Spectroscopic investigations performed at the neutron drip line have recently confirmed such predictions showing that the 24O is a doubly magic nucleus (Z = 8, N = 16). Predictions within the shell model calculation for the 23,24O ground state have been confirmed measuring their spectroscopic factors. Results obtained in one‐neutron removal reactions performed by using in‐flight radioactive ion beams produced at the Fragment Separator FRS of GSI are reported.

The nuclei Ca-47 and Ti-55 were populated in one-neutron knock-out reactions at relativistic energies. Momentum distributions of the residual nuclei as well as gamma-ray spectra were measured at the GSI fragment separator (FRS). Preliminary results of the ongoing analysis including cross sections and spin/parity assignments are presented.

Dipole strength distributions were determined for the neutron‐rich nuclei 129–132Sn and 133,134Sb from electromagnetic excitation in an experiment using the FRS‐LAND setup. For all nuclei, a sizeable fraction of “pygmy” dipole strength at excitation energies well below the giant dipole resonance was observed. The integrated low‐lying dipole strength of the nuclei with low neutron separation energies can be compared to results for stable nuclei (e.g. N = 82 isotopes) determined for the energy regime of 5–9 MeV. A clear increase of the dipole strength with increasing asymmetry of the nuclei is observed. Comparing the ratio of the low‐lying dipole over the giant dipole strength to recent relativistic mean field calculations, values for the parameters a4 and p0 of the symmetry energy and for the neutron skin thickness are derived. Averaged over 130Sn and 132Sn we extract ā4 = 31.8±1.3 MeV and p0 = 2.2±0.5 MeV/fm3. The neutron skin sizes are determined to Rn‐Rp = 0.23±0.03 fm and 0.24±0.03 fm for 130Sn and 13...

The combination of the in‐flight separator FRS and the storage‐ring ESR at GSI offers unique possibilities for high accuracy mass and lifetime measurements of bare and few‐electron fragments. Operating the ESR in the isochronous mode allows for measurements of revolution frequencies of stored ions without cooling. Isochronous Mass Spectrometry (IMS) can be applied to fragments with half‐lives as short as several tens of microseconds. Newly developed magnetic rigidity tagging increases the resolving power of IMS to about 500000. IMS can be used to measure masses of nuclei with rates even lower than one ion per day, a property also needed for the purpose of the ILIMA project at the future facility FAIR.

The ground state structure of the near drip‐line 23O nucleus and neutron‐rich 17,21O isotopes has been investigated at GSI via exclusive measurements of one‐neutron Coulomb breakup reactions with a Pb target using secondary beams of the corresponding projectiles at 400–600 MeV/u. Differential cross sections for electromagnetic dissociation have been measured and compared with the calculated ones in a direct breakup model. The cross section dσ/dE* (excitation energy E*), further differentiated according to the observed (excited) states of the remaining nucleus, provides spectroscopic information on the ground state of these nuclei.

We describe the large acceptance magnetic spectrometer called MAGNEX. It will be used in nuclear reaction experiments with both stable and radiactive beams at the LNS-INFN laboratory, Catania, Italy.

The 11B(7Li,7Be)11Be reaction at 57 MeV incident energy was used to explore the 11Be excitation energy spectrum at forward angles. Angular distributions were extracted for the transitions to the ground and to the states of 11Be at excitation energies of E*=0.32,1.78,2.69,3.41,3.89,3.96,6.05 MeV combined with the ground and the first excited state of 7Be. Also the SDR [1][2] oscillation mode was observed at E*=9.5 MeV and FWHM≈9 MeV and a new peak at E*=6.05 MeV and FWHM≈0.3 MeV was observed. QRPA calculations in the G-matrix representation are in progress in order to describe the continuum structure of 11Be. DWBA calculations have been started to evaluate transferred angular momenta both in the one step and in the two steps dynamical framework.