| 1. |
- Aleksandrov, D., et al.
(författare)
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Invariant mass spectrum and alpha-n correlation function studied in the fragmentation of He-6 on a carbon target
- 1998
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Ingår i: Nuclear Physics A. - 0375-9474. ; 633:2, s. 234-246
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Tidskriftsartikel (refereegranskat)abstract
- Momentum distributions and invariant mass spectra from the breakup of He-6 ions with an energy of 240 MeV/u interacting with a carbon target have been studied. The data were used to extract information about the reaction mechanism which is influenced by the structure of He-6. It is found that the dominant reaction mechanism is a two-step process: knock out of one neutron followed by the decay of the He-5 resonance. The shape of the (alpha+n) two-body invariant mass spectrum is interpreted as mainly reflecting the 5He ground state which is a J(pi) = 3/2(-) resonance. However, no evidence for correlations between cu particles and neutrons is observed in the momentum widths of the distributions. It is demonstrated that a combined analysis of the two-body invariant mass spectrum and an appropriate correlation function may be used to determine the properties of the intermediate resonance. (C) 1998 Elsevier Science B.V.
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| 2. |
- Anne, R., et al.
(författare)
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Exclusive and Restricted-Inclusive Reactions Involving the Be-11 One-Neutron Halo
- 1994
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Ingår i: Nuclear Physics A. - : Elsevier BV. - 0375-9474. ; 575:1, s. 125-154
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Tidskriftsartikel (refereegranskat)abstract
- Reactions of a 41 MeV/u beam of the radioactive halo nucleus Be-11 have been studied with a counter telescope coupled to an array of neutron detectors covering angles up to 97-degrees. The technique allows to determine single-neutron inclusive and exclusive angular distributions. The targets (Be, Ti and Au) were chosen to illustrate the relative roles played by nuclear and Coulomb mechanisms. The channels leading to Be-10, the dissociation channels, correspond to impact parameters larger than the sum of the radii of the target and the Be-10 core. It is shown that for the dissociation process it is possible to account almost quantitatively for the integral, single- and double-differential cross sections from models without free parameters including the Coulomb, Serber and Glauber (diffraction-dissociation) mechanisms. The neutron distributions from the nondissociative reaction channels show little individuality and it is convenient to group them together as the channel ''neutron plus anything different from Be-10''. We refer to these as ''restricted-inclusive'' reactions. These seem to be a promising tool for obtaining accurate information on the halo wave function in momentum coordinates.
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| 3. |
- Borge, M. J. G., et al.
(författare)
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Probing the Li-11 halo structure through beta-decay into the Be-11(*) (18 MeV) state
- 1997
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Ingår i: Nuclear Physics A. - 0375-9474. ; 613:3, s. 199-208
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Tidskriftsartikel (refereegranskat)abstract
- An experimental study of beta-delayed charged particles (H, He, Be) from Li-11 shows a beta-feeding to an excited state at 18.15(15) MeV in Be-11 with a large Gamow-Teller strength, B-GT greater than or equal to 1.6. Branching ratios and reduced widths of 2-, 3- and 5- particle decay channels of this state are extracted, A strong suppression of the neutron branch from the 18 MeV state to the Be-10(g.s.) is observed, We suggest that the measured partial width may be sensitive to the (p(1/2))(2) component in the Li-11 halo, A rough estimate indicates that the (p(1/2))(2) component is not the dominant one in the halo wave-function.
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| 4. |
- Mukha, I., et al.
(författare)
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Super-strong beta-decay of Li-11 into Be-11* (18 MeV) state: A probe for halo p-wave component?
- 1997
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Ingår i: Nuclear Physics A. - 0375-9474. ; 616:1-2, s. C201-C207
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Konferensbidrag (refereegranskat)abstract
- An experimental study of beta-delayed charged particles (H, He, Be), neutrons and gamma-rays that follow the Li-11 beta-decay, clearly indicates a beta-feeding to an exited state at 18.1 MeV in Be-11 with a large Gamow-Teller strength, B-GT greater than or equal to 1.0. The large strength of this beta-transition implies a broad overlap of the Be-11* state at 18.1 MeV and the ground state of Li-11. The deduced width of this resonance is similar or equal to 1 MeV. A strong suppression of the branch from 18.1 MeV state into the Be-10+n channel is observed. This branch, with the largest decay energy, has a partial width less than 1% of the total width. A centrifugal barrier consideration fails to explain this effect. A possible consequence of the observed effect for the Li-11 structure is that the admixture of (p(1/2))(2) configuration in Li-11 might be small.
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| 5. |
- Zinser, M., et al.
(författare)
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Invariant-mass spectroscopy of Li-10 and Li-11
- 1997
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Ingår i: Nuclear Physics A. - 0375-9474. ; 619:1-2, s. 151-176
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Tidskriftsartikel (refereegranskat)abstract
- 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 similar to 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. (C) 1997 Elsevier Science B.V.
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| 6. |
- Aleksandrov, D., et al.
(författare)
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Halo excitations in fragmentation of He-6 at 240 MeV/u on carbon and lead targets
- 2000
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Ingår i: Nuclear Physics A. - 0375-9474. ; 669:1-2, s. 51-64
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Chulkov, L. V., et al.
(författare)
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Three-body correlations in electromagnetic dissociation of Borromean nuclei: The He-6 case
- 2005
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Ingår i: Nuclear Physics A. - : Elsevier BV. - 0375-9474. ; 759:1-2, s. 23-42
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Tidskriftsartikel (refereegranskat)abstract
- Dissociation of He-6 on a lead target has been studied at 240 MeV/u. The four-momenta of the two neutrons in coincidence with alpha-particles have been measured and used to reconstruct the three-body energy and angular correlations in the final state. For the first time, three-body correlations were included in the analysis of the He-6 dissociation data, and compared with calculations assuming a dipole mode for the electromagnetic dissociation. In addition, the experimental data have been analyzed using a series expansion of the final transition amplitude into hyperspherical functions, showing the importance of both nn and alpha n final-state interactions. It is shown that the dissociation process is governed by a transition of one neutron from the p-shell in the 6He ground state to the s-shell in the continuum further indicating that the role of the transition through an intermediate He-5(3/2(-)) state is more important than expected. (c) 2005 Elsevier B.V. All rights reserved.
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| 8. |
- Jeppesen, H. B., et al.
(författare)
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Low energy reactions with radioactive ions at REX-ISOLDE - the Li-9+H-2 case
- 2005
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Ingår i: Nuclear Physics A. - : Elsevier BV. - 0375-9474. ; 748, s. 374-374
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Tidskriftsartikel (refereegranskat)abstract
- At the newly constructed postaccelerator REX-ISOLDE (Radioactive beam Experiment at ISOLDE) we have investigated reactions induced by a Li-9 beam incident on a deuterium target at an energy of 2.36 MeV/u. Most reaction channels were recorded. From one-neutron transfer the differential cross-section for the low lying Li-10 spectrum is found. The results from the other channels demonstrate the great applicability and many possibilities that REX-ISOLDE opens up.
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| 9. |
- Johansson, Håkan T, 1977, et al.
(författare)
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The unbound isotopes He-9,He-10
- 2010
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Ingår i: Nuclear Physics A. - Elsevier : Elsevier BV. - 0375-9474 .- 1873-1554. ; 842:1-4, s. 15-32
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Tidskriftsartikel (refereegranskat)abstract
- The unbound nuclei He-9 and He-10 have been produced in proton-knockout reactions from a 280 MeV/u Li-11 beam impinging on a liquid hydrogen target at the ALADIN-LAND setup at GSI. Information on their nuclear structure has been obtained from the relative-energy spectra, He-8 + n and He-8 + 2n, employing reaction models incorporating the structure of Li-11. The (8H)e + n relative-energy spectrum is dominated by a strong peak-like structure at low energy, which may be interpreted within the effective-range approximation as the result of an s-wave interaction with a neutron scattering length of -3.17(66) fm. This spectrum also shows evidence for resonance states at 1.33(8) MeV and at 2.4 MeV above the He-8 + n threshold. It is argued that the s-state might not be the He-9 ground state. For He-8 + n + n, the analysis of the relative-energy spectrum gives two alternative possibilities for an interpretation: either a narrow resonance at 1.42(10) MeV (Gamma = 1.11(76) MeV) superimposed on a correlated background, or two overlapping resonances, a ground state at 1.54(11) MeV (Gamma = 1.91(41) MeV) together with an excited state at 3.99(26) MeV (Gamma = 1.64(89) MeV). The two possible interpretations are discussed. (C) 2010 Elsevier B.V. All rights reserved.
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| 10. |
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