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Título : Continuum excitations in He-6
Autor : Aumann, T., Aleksandrov, D., Axelsson, L., Baumann, T., García Borge, María José, 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., 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, Zhukov, M. V.
Palabras clave : [PACS] Breakup and momentum distributions
[PACS] Coulomb excitation
[PACS] Properties of specific nuclei listed by mass ranges:6 ≤ A ≤ 19
[PACS] Neutron spectroscopy
Fecha de publicación : Mar-1999
Editor: American Physical Society
Resumen: 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.
Descripción : 11 pages, 2 tables, 6 figures.-- PACS nrs.: 27.20.+n; 25.60.Gc; 25.70.De; 29.30.Hs.
Versión del editor:
ISSN: 0556-2813
DOI: 10.1103/PhysRevC.59.1252
Citación : Physical Review C 59(3): 1252-1262 (1999)
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