Search

Coulomb break up of the neutron-rich 15,17 C and 17–22 O isotopes has been studied experimentally using secondary beams at energies of 500–600 MeV/u. A comparison between differential cross sections, d σ/ d E ∗ , with that obtained from a binary model shows that the main ground-state configuration of 15 C is 14 C(0 + )⊗ ν S 1/2 as expected. For 17 C, our preliminary data analysis reveals that the predominant (∼64%) configuration of the ground state is 16 C(2 + )⊗ ν s , d . For 17–22 O, the low-lying E1 strength amounts up to about 12% of the energy weighted sum rule strength depending on neutron number. The energy weighted E1 strength (integrated up to 15 MeV excitation energy) increases up to 20 O then decreases for 21,22 O. These data are compared to a shell model calculation.

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.

In heavy ion collisions at near relativistic energies, electromagnetic excitation of the double giant dipole resonance occurs with large cross sections. We summarize the presently available experimental data and discuss related theoretical efforts. Emphasis is paid to the question of anharmonicities and to the damping of the two-phonon states.

A = 140–148 even-even barium nuclei produced in the spontaneous fission of 248Cm were studied using the EUROGAM2 array. Spins and parities of excited levels have been firmly established from triple-γ angular correlation and direction-polarization correlation measurements. Known band structures have been extended and new bands were found. Band-crossing phenomena have been studied, which suggest termination of an alternating-parity band by particle alignment in 146Ba. The new data for 148Ba confirm predictions of a local decrease of electric dipole moment in 146Ba.

We report on Coulomb dissociation experiments utilizing a 208 Pb-beam (641 MeV/nucleon) impinging on C, Sn, Ho, Pb and U targets. Excitation energy distributions for 208 Pb are extracted from an exclusive measurement of the projectile decay products. The measured cross section is dominated for heavy targets by Coulomb excitation of giant resonance states in lead. A thorough analysis yields evidence for the excitation of the double-phonon giant dipole resonance. In contrast to earlier results obtained for other nuclei the extracted cross section for 208 Pb exceeds that of theoretical predictions on the basis of a harmonic oscillator scenario only slightly by about a factor 1.3.

g-factors of excited states in 154Dy were measured up to high spins. A method that combines the recoil-distance technique with the use of the large transient magnetic fields was applied. The measurement was sensitive only to states which were populated ≈ 13.5 ps after the nuclear reaction. Hence the influence of unobserved quasi-continuum feeding states on the measured precession angles was minimized. The results are compared with calculated g-factors. They can be explained by the neutron i 13 2 alignment in the positive- and negative-parity sequences at medium spins. They also confirm the predicted alignment of protons in the band termination region of spins I ⩾ 30kh.