[en] The dipole response of stable and unstable neutron-rich oxygen nuclei of masses A=17 to A=22 has been investigated experimentally utilizing electromagnetic excitation in heavy-ion collisions at beam energies about 600 MeV/nucleon . A kinematically complete measurement of the neutron decay channel in inelastic scattering of the secondary beam projectiles from a Pb target was performed. Differential electromagnetic excitation cross sections dσ/dE were derived up to 30MeV excitation energy. In contrast to stable nuclei, the deduced dipole strength distribution appears to be strongly fragmented and systematically exhibits a considerable fraction of low-lying strength

[en] The electromagnetic excitation process at beam energies around 500 MeV/u is utilized to probe the dipole response of light neutron-rich nuclei. The secondary beams are produced in fragmentation reactions and separated by the GSI fragment separator FRS. By measuring the neutron decay after inelastic scattering on a Pb target in a kinematically complete experiment, the differential electromagnetic excitation cross sections dσ/dE* are derived. The oxygen isotope chain is studied systematically ranging from A=17 to A=22. Low-lying dipole strength is observed, exhausting about 10% of the energy-weighted dipole sum rule for excitation energies below 15 MeV. Even though this soft dipole excitation is present in all neutron-rich oxygen isotopes investigated, the cluster sum rule associated with the dipole motion of the valence nucleons against the ¹⁶O core is only fully exhausted for ¹⁸O. For the halo nuclei ¹¹Be and ^15,17C it is shown that detailed spectroscopic information on the ground state single particle structure can be deduced from the 'threshold' dipole strength. (author)

[en] The excitation of the double-phonon giant dipole resonance was observed in heavy projectile nuclei impinging on targets of high nuclear charge with energies of 500-700 MeV/nucleon. New experimental data are presented for ¹³⁶Xe and ²³⁸U together with further analysis of earlier data on ²⁰⁸Pb. Differential cross sections dσ/dE^* and dσ/dθ for electromagnetic excitations were deduced. Depending on the isotope, cross sections appear to be enhanced in comparison to those expected from a purely harmonic nuclear dipole response. The cumulative effect of excitations of two-phonon states composed of one dipole and one quadrupole phonon, of predicted anharmoniticies in the double-phonon dipole response, and of damping of the dipole resonance during the collision may account for the discrepancy. In addition, decay properties of two-phonon resonances were studied and compared to that of a statistical decay. (orig.)

[en] Electromagnetic and nuclear breakup of the neutron-rich Oxygen isotopes ranging from A=17 to A=22 is studied experimentally in reactions at energies around 600 MeV/u. The beams were produced in fragmentation reactions and separated by the GSI Fragment Separator FRS. By measuring the four-momenta of all decay products after inelastic scattering and neutron decay of the projectile, the excitation energy is determined. From the differential cross sections dσ/dE^* for electromagnetic excitation, the E1-strength distributions can be deduced. For ^18,20,22O, low-lying dipole strength is observed, exhausting about 5% of the Thomas Reiche Kuhn sumrule for energies up to 5 MeV above the continuum threshold

No abstract available

[en] Dissociation of 227 MeV/u ⁸He in a carbon target has been studied in kinematically complete experiments. The data include the relative energy spectrum, angular distributions in the neutron knock-out channel (⁶He+n) as well as diffractive dissociation and inelastic scattering into the (⁶He+2n) channel. The data are compared with corresponding results from the well-known halo nucleus ⁶He. In both cases it is found that neutron knock-out is the dominating reaction channel. The relative energy spectrum (⁶He+n) shows a structure, which is interpreted as being due to the I^π=3/2^- resonance in the ⁷He ground state with about equal contribution from its I^π=1/2^- spin-orbit partner. The ⁷He resonance shows a spin alignment similar to that observed in ⁵He, but with a smaller anisotropy indicating that the structure of the ⁸He ground state is more complicated than that of ⁶He. The data in the (⁶He+2n) channel were used to identify resonances in the excitation energy spectrum of ⁸He. If the spectrum is interpreted as two overlapping resonances, the spin-parity assignment for these is found to be 2⁺ and 1^-, respectively

[en] The cross section for the ⁶He+n channel as a function of the relative energy shows a structure, which is interpreted as being due to the ⁷He I^π=3/2^- ground state resonance with about equal contribution from its I^π=1/2^- spin-orbit partner at 1.2(2) MeV with a width Γ=1.0(2) MeV. (orig.)

No abstract available

[en] A scintillating fibre detector for relativistic heavy ions with an active area of 50 x 50 cm² has been developed and was tested with various ion beams (1≤Z≤92). At count rates of up to 10⁵ particles/s, the position resolution was found to be determined by the fibre width of 1 mm; depending on the nuclear charge of the beam, efficiencies between 89% and 100% and time resolutions between 800 and 200 ps (FWHM) were obtained. (orig.)

[en] Dissociation of a 240 MeV/u beam of ⁶He, incident on carbon and lead targets, has been studied in kinematically complete experiments to investigate low-lying excitation modes in the halo nucleus ⁶He. It is shown that alignment effects characterize the inelastic scattering and allow an unambiguous assignment of the spin of a narrow resonance observed in the excitation energy spectrum. The differential cross sections for the ⁶He inelastic scattering on carbon and lead targets were deduced from the measured momenta of the two neutrons and the α-particle. An analysis of these distributions shows that quadrupole and, possibly, monopole excitations characterize the hadronic interaction, while the dipole mode is dominating in Coulomb dissociation. Neither theoretically predicted new resonance states in ⁶He nor nuclear excitation of a dipole mode were found. Direct evidence has been obtained for strong suppression of Coulomb post-acceleration in direct Coulomb breakup in a lead target