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36 pages, 10 figures, 8 tables, 3 appendices.-- PACS nrs.: 27.20.+n; 24.70.+s.-- Printed version published Jul 15, 2007., Fragmentation reactions in a carbon target with beams of Li-11 and Be-14 at relativistic energies have been studied in a kinematically complete experiment at the ALADIN-LAND setup at GSI. Excited states in Li-11 and Be-14 were obtained from the data in the inelastic channel. The measured cross sections with the core nucleus in the final state show that in the Be-14 case core polarization plays an important role. In the one-neutron knockout channels the measured angular correlations between fragment and neutron are asymmetric, which demonstrates the presence of states with different parities in the Li-11 and Be-14 ground states. For Li-10 a low-lying virtual s-state, a p-state and evidence for a d-state could be extracted from the data, while the Be-12 + n system shows resonances with more complicated structure., This work was supported by the BMBF under Contracts No. 06 DA 115, No. 06 OF 838 and No. 06 MZ 864 I and by GSI via Hochschulzusammenarbeitsvereinbarungen under Contracts No. DA RICK, No. OF ELZ, No. MZ KRAK and partly supported by the Polish Committee of Scientific Research under Contract No. KBN/2P03B/144/10, CICYT under Contract No. FPA2005-02379 (MJGB, OT), RFBR under Contract No. 04-02-17251, EC under Contract No. ERBCHGE-CT92-0003, and under the auspices of the US Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract No.W-7405-Eng-48. One of us (T.N.) is a Royal Swedish Academy of Sciences Research Fellow supported by a grant from the Knut and Alice Wallenberg Foundation.

Investigation of one-proton knockout channel from 6He impinging on a carbon target was performed. The triton fragments originating from this channel were detected in coincidence with the two neutrons. A broad structure was observed in the t + n + n-relative energy spectrum. The observed structure cannot be attributed to background process.

4 pages, 1 table, 3 figures.--PACS nrs.: 27.10.+h; 21.10.Pc; 25.60.Gc, The one-proton knockout channel from He-6 (240 MeV/u) impinging on a carbon target has been investigated. The triton fragments originating from this channel were detected in coincidence with the two neutrons. A broad structure, peaked at 3 MeV above the t+2n threshold, is observed in the t+n+n-relative energy spectrum. It is shown that this structure is mainly due to a I-pi=1/2(+) resonance as expected for the H-5 ground state, and from the observed angular and energy correlations, being used for the first time in H-5 studies, that the neutrons to a large extent occupy the p shell., This work was supported by the BMBF under Contracts No. 06 DA 925 I, No. 06 OF 838, and No. 06 MZ 864 I, and by GSI via Hochschulzusammenarbeitsvereinbarungen under Contracts No. DARIC, No. OF ELZ, No. MZ KRAK, and partly supported by the Polish Committee of Scientific Research under Contract No. KBN/2P03B/144/10, CICYT under Contract No. AEN99-1046-C02-02 (M. J.G. B., O.T.), RFBR under Contract No. 01-02-16685, and EC under Contract No. ERBCHGE-CT92-0003. One of us (B. J.) acknowledges support from the Alexander von Humboldt Research Foundation.

The one-proton knockout channel from [Formula presented] ([Formula presented]) impinging on a carbon target has been investigated. The triton fragments originating from this channel were detected in coincidence with the two neutrons. A broad structure, peaked at 3 MeV above the [Formula presented] threshold, is observed in the [Formula presented]-relative energy spectrum. It is shown that this structure is mainly due to a [Formula presented] resonance as expected for the [Formula presented] ground state, and from the observed angular and energy correlations, being used for the first time in [Formula presented] studies, that the neutrons to a large extent occupy the [Formula presented] shell.

14 pages, 6 figures.-- PACS nrs.: 27.20.+n; 24.70.+. Dissociation of a 240 MeV/u beam of He-6, incident on carbon and lead targets, has been studied in kinematically complete experiments to investigate low-lying excitation modes in the halo nucleus He-6. 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 He-6 inelastic scattering on carbon and lead targets were deduced from the measured moments of the two neutrons and the a-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 He-6 nor nuclear excitation of a dipole mode were found. Direct evidence has been obtained for strong suppression of Coulornb post-acceleration in direct Coulomb breakup in a lead target. This work was supported by the BMBF under Contracts 06 DA 820, 06 OF 112 and 06 MZ 864 and by GSI via Hochschulzusammenarbeitsvereinbarungen under Contracts DA RICK, OF ELZ, MZ KRK and partly supported by the Polish Committee of Scientific Research under Contract PBZ/PB03/113/09, EC under contract ER-BCHGE-CT92-0003, CICYT under contract AEN92-0788-C02-02 MJGB.and WTZ under contract RUS 609-96. One of us (B.J.) acknowledges the support through an Alexander von Humboldt Research Award.

11 pages, 2 tables, 6 figures.-- PACS nrs.: 27.20.+n; 25.60.Gc; 25.70.De; 29.30.Hs., The three-body breakup He-6 --> He-4 + n + n is studied experimentally, using a secondary He-6 ion beam of 240 MeV/nucleon incident on carbon and lead targets. integrated cross sections for one- and two-neutron knockout and differential cross sections dσ/dE* and dσ/dΘ for inelastic nuclear or electromagnetic excitations into the He-6 continuum are presented. The E1-strength distribution is deduced from electromagnetic cross sections and is found to exhaust (10 ± 2)% of the energy-weighted Thomas-Reichr-Kuhn sum rule or (40 ± 8)% of the cluster sum rule for excitation energies below 5 MeV. Both the energy-weighted and non-energy-weighted dipole cluster sum rules are almost exhausted integrating the strength up to 10 MeV, a fact from which the root-mean-square distance between the a core and the two valence neutrons of r(α-2n) = (3.36 ± 0.39) fm is derived. The known I(π) = 2(+) (1.80 MeV) resonance in He-6 is observed in nuclear inelastic scattering; model-dependent values of the quadrupole deformation parameter δ(2) = (1.7 ± 0.3) fm or B (E2,0(+) --> 2(+)) = (3.2 ± 0.6)e(2) fm(4) are derived. No clear signature could be obtained for predicted higher-lying 2(+) resonances, but low-lying continuum strength of multipolarity other than dipole, likely of monopole and quadrupole multipolarity, is indicated by the data. Two-body correlations in the decaying He-4 + n + n system are investigated. The astrophysical relevance of the data with regard to the two-neutron capture process He-4(2n, γ) He-6 is briefly discussed., This work was supported by the German Federal Minister for Education and Research (BMBF) under Contracts No. 06 DA 820, 06 OF 474 and 06 MZ 864 and by GSI via Hochschulzusammenarbeitsvereinbarungen under Contracts No. DARIK, No. OF ELK, MZ KRK and partly supported by the Polish Committee of Scientific Research under Contract No. PB2/P03B/113/09, EC under Contract No. ERBCHGECT92-0003, and the Spanish CICYT under Contract No. AEN92-0788-C02-02 (M.J.G.B.), and by Deutsche Forschungsgemeinschaft (DFG) under Contract No. 436 RUS 130/127/1. One of us (B.J.) acknowledges support through an Alexander von Humboldt Senior Research Scientist Award.

26 pages, 5 tables, 10 figures.-- PACS nrs.: 25.60.+v; 27.20.+n; 25.70.Mn; 25.70.De., Break-up of secondary Li-11 ion beams (280 MeV/nucleon) on C and Pb targets into Li-9 and neutrons is studied experimentally. Cross sections and neutron multiplicity distributions are obtained, characterizing different reaction mechanisms. Invariant-mass spectroscopy for Li-11 and Li-10 is performed. The E1 strength distribution, deduced from electromagnetic excitation of Li-11 up to an excitation energy of 4 MeV comprises ~8% of the Thomas-Reiche-Kuhn energy-weighted sumrule strength. Two low-lying resonance-like structures are observed for Li-10 at decay energies of 0.21(5) and 0.62(10) MeV, the former one carrying 26(10)% of the strength and likely to be associated with an s-wave neutron decay. A strong di-neutron correlation in Li-11 can be discarded. Calculations in a quasi-particle RPA approach are compared with the experimental results for Li-10 and Li-11., The authors are indebted to the staff personel of the GSI accelerator group and of the target laboratory for their support. We acknowledge support by the German Federal Minister for Research and Technology (BMBF) under Contracts 06DA 665 I, 06OF 112 and 06MZ 465, by GSI under Contracts DA RIK, OF ELZ, MZ KRK, by the Polish Committee of Scientific Research under Contract PBZ/PB03 / 113/09, EC under contract ERBCHGE-CT92-0003 and by the Spanish CICYT under contract AEN92-0788-C02-02(MJGB).

4 pages, 2 figures.-- PACS nrs.: 25.60.Gc, 24.70.+s, 27.10.+h., Peripheral fragmentation of a 240 MeV/nucleon beam of the halo nucleus He-6 incident on carbon target has been studied in a kinematically complete experiment. It is found that one-neutron stripping to the unbound nucleus He-5 is the dominant fragmentation mechanism and that it leads to a spin alignment of He-5 in a plane perpendicular to the He-5 momentum vector. This is expected to be a common feature for all neutron halo nuclei., This work was supported by the BMBF under Contracts No. 06 DA 665 I, No. 06 OF 112, and No. 06 MZ 465 and by GSI via Hochschulzusammenarbeitsvereinbarungen under Contracts No. DA RICK, No. OF ELZ, and No. MZ KRK, as well as partly supported by the Polish Committee of Scientific Research under Contract No. PBZyPB03y113y09, EC under Contract No. ERBCHGE-CT92-0003, and CICYT under Contract No. AEN92-0788-C02-02 (MJGB).

4 pages, 3 figures.-- PACS nrs.: 25.60.+v, 21.10.Pc, 25.70.Mn, 27.20.+n., Reactions of the halo systems Be-11 and Li-11 (at 460 and 280 MeV/nucleon) with a carbon target demonstrate that (n + Li-9) has an (unbound) l = 0 ground state very close to the threshold. The neutron halo of Li-11 has appreciable (1s(1/2))(2) and (0p(1/2))(2) components., This work was supported by the German Federal Minister for Research and Technology (BMFT) under Contracts No. 06 DA 641 1, No. 06 Bü 103, and No. 06 MZ 465 and by GSI via Hochschulzusammenarbeitsvereinbarugen under Contracts No. DA RICK, BO FRE, F ELE, MZ Krak, and partly supported by the Polish Committee of Scientific Research under Contraet No. PB1158/P3/92/02.

4 pages, 3 figures, 2 tables., Extremely neutron-rich nuclei exhibit a number of interesting features of which the most well-known is the neutron halo phenomenon found in 11Li. See e.g. ref. [1] for a recent review. A much less investigated nucleus is 8He, although it is the nucleus with the highest A/Z-ratio that is still stable against particle emission. In the first experiment where evidence for an anomalously large matter radius in 11Li was seen [2], similar effects were also found in 6He and 8He. The extended neutron distribution has previously mainly been probed in dissociation experiments [3] at 800 MeV/u. We present here further information on reactions involving 8He.