Electromagnetic excitation of the two-phonon giant dipole resonance

The nuclear response of "1"3"6Xe and "2"0"8Pb to electromagnetic excitation was studied in peripheral, near-relativistic heavy-ion collisions. Large cross sections were observed for the one-phonon and two-phonon isovector giant dipole resonance. The results, in particular the unexpectedly large strength found for the double giant dipole resonance, are discussed and compared to that of other recent measurements. (orig.)Available from TIB Hannover: RO 801(93-72) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Two-phonon giant dipole resonance in "2"0"8Pb

Excitation of the two-phonon isovector giant dipole resonance was observed in "2"0"8Pb projectiles incident on different target nuclei (C, Sn, Ho, Pb, U) at high energy (640 A.MeV). Evidence is found for a two-step electromagnetic excitation mechanism. An enhancement of 1.33(16) for the excitation cross section is observed relative to the harmonic approximation. Neutron- and #gamma#-decay probabilities are derived as well. (orig.)SIGLEAvailable from TIB Hannover: RO 801(96-27) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Electromagnetic excitation of the double giant dipole resonance in "1"3"6Xe

Available from TIB Hannover: RO 801(92-64) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Exclusive studies of neutron and charged particle emission in collisions of "1"9"7Au+"1"9"7Au at 400 MeV/nucleon

We present data on collective flow of neutrons in collisions of "1"9"7Au+"1"9"7Au at 400 MeV/nucleon. The azimuthal distribution about the beam axis is investigated with respect to the reaction plane as determined from light charged particles. The 'squeeze-out' of neutrons, perpendicular to the reaction plane, is observed for the first time. Quantitative agreement to a high level of accuracy is found between the behaviour of neutrons and hydrogen ions. (orig.)Accepted for publication by Phys. Rev. Lett.SIGLEAvailable from TIB Hannover: RO 801(93-60) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Energy dependence of collective flow of neutrons and charged particles in "1"9"7Au+"1"9"7Au collisions

Our contribution focusses on one particular aspect of collective flow of nuclear matter: the so-called ''squeeze-out'', i.e. the preferential emission of mid-rapidity particles perpendicular to the reaction plane. The data were taken for the system "1"9"7Au + "1"9"7Au at 400, 600 and 800 MeV/u. We cover two topics, the comparison of neutrons and protons, and the bombarding energy dependence of the neutrons' squeeze-out. (orig.)Available from TIB Hannover: RO 801(94-02) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Charge-pickup of "2"3"8U at relativistic energies

Cross sections for the charge-pickup of "2"3"8U projectiles were measured at E/A=600 and 1000 MeV for seven different targets (Be, C, Al, Cu, In, Au and U). Events with two fission fragments with a sum charge of 93 in the exit channel were selected. Due to the significant excitation energy, the dominant part of produced Np nuclei fission instead of decaying to the ground state by evaporation. The observed cross sections can be well reproduced by intranuclear-cascade-plus-evaporation calculations and, therefore, confirm recent results that no exotic processes are needed to explain charge-pickup processes. (orig.)24 refs.Available from TIB Hannover: RO 801(95-60) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Probing the nuclear liquid-gas phase transition

Fragment distributions resulting from Au+Au collisions at an incident energy of E/A=600 MeV are studied. From the measured fragment and neutron distributions the mass and the excitation energy of the decaying pre-fragments were determined. A temperature scale was derived from observed yield ratios of He and Li isotopes. The relation between this isotope temperature and the excitation energy of the system exhibits a behavior which is expected for a phase transition. The nuclear vapor regime takes over at an excitation energy of 10 MeV per nucleon, a temperature of 5 MeV and may be characterized by a density of 0.15-0.3 normal nuclear density. (orig.)55 refs.SIGLEAvailable from TIB Hannover: RO 801(95-13) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Total and nuclear fission cross sections of "2"3"8U at relativistic energies

Total fission cross sections of "2"3"8U projectiles were measured at bombarding energies of 0.6 and 1 GeV per nucleon for seven different targets (Be, C, Al, Cu, In, Au and U). It is found that all data points fall onto one curve, independent of bombarding energy, once the electromagnetic contribution to the total fission cross sections is subtracted. The abrasion-ablation model predicts a significantly weaker target dependence than observed, and underestimates the nuclear fission cross sections for the heavier targets. (orig.)SIGLEAvailable from TIB Hannover: RO 801(96-11) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Electromagnetic fission of "2"3"8U at 600 and 1000 MeV per nucleon

Electromagnetic fission of "2"3"8U projectiles at E/A=600 and 1000 MeV was studied with the ALADIN spectrometer at the heavy-ion synchrotron SIS. Seven different targets (Be, C, Al, Cu, In, Au and U) were used. By considering only those fission events where the two charges added up to 92, most of the nuclear interactions were excluded. The nuclear contributions to the measured fission cross sections were determined by extrapolating from beryllium to the heavier targets with the concept of factorization. The obtained cross sections for electromagnetic fission are well reproduced by extended Weizsaecker-Williams calculations which include E1 and E2 excitations. The asymmetry of the fission fragments' charge distribution gives evidence for the excitation of the double giant-dipole resonance in uranium. (orig.)SIGLEAvailable from TIB Hannover: RO 801(95-28) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Neutron momentum distribution from ''core break-up'' reactions of halo nuclei

Neutron angular distributions from violent break-up reactions of "1"1Li and "1"1Be have been measured at 28 MeV/u and 280 MeV/u and at 41 MeV/u and 460 MeV/u, respectively. The derived neutron momentum distributions show a narrow component in transverse momentum that is within uncertainties independent of beam energy and target charge. This component is suggested to be simply related to the momentum distribution of the loosely bound halo neutron(s) in the projectiles. (orig.)SIGLEAvailable from TIB Hannover: RO 801(95-02) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman