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Continuum excitations in He-6

AuthorsAumann, T.; Aleksandrov, D.; Axelsson, L.; Baumann, T.; García Borge, María José CSIC ORCID; Chulkov, L. V.; Cub, J.; Dostal, W.; Eberlein, B.; Elze, Th. W.; Emling, H.; Geissel, H.; Goldberg, V. Z.; Golovkov, M.; Grünschloβ, A.; Hellström, M.; Hencken, K.; Holeczek, J.; Holzmann, R.; Jonson, B.; Korshenninikov, A. A.; Kratz, J. V.; Kraus, G; Kulessa, R.; Leifels, Y.; Leistenschneider, A.; Leth, T.; Mukha, I. CSIC ORCID; Münzenberg, G.; Nickel, F.; Nilsson, T.; Nyman, G.; Petersen, B.; Pfützner, M.; Richter, Achim W.; Riisager, K.; Scheidenberger, C.; Schrieder, G.; Schwab, W.; Simon, H.; Smedberg, M. H.; Steiner, M.; Stroth, J.; Surowiec, A.; Suzuki, T.; Tengblad, Olof CSIC ORCID ; Zhukov, M. V.
Keywords[PACS] Breakup and momentum distributions
[PACS] Coulomb excitation
[PACS] Properties of specific nuclei listed by mass ranges:6 ≤ A ≤ 19
[PACS] Neutron spectroscopy
Issue DateMar-1999
PublisherAmerican Physical Society
CitationPhysical Review C 59(3): 1252-1262 (1999)
AbstractThe 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.
Description11 pages, 2 tables, 6 figures.-- PACS nrs.: 27.20.+n; 25.60.Gc; 25.70.De; 29.30.Hs.
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