Coulomb and nuclear breakup of a halo nucleus 11Be

By N. Fukuda, T. Nakamura, N. Aoi, N. Imai, M. Ishihara, T. Kobayashi, H. Iwasaki, T. Kubo, A. Mengoni, M. Notani and 6 more. 2004

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Breakup reactions of the one-neutron halo nucleus {sup 11}Be on lead and carbon targets at about 70 MeV/nucleon have been investigated at RIKEN by measuring the momentum vectors of the incident {sup 11}Be, outgoing {sup 10}Be, and neutron in coincidence. The relative energy spectra as well as the angular distributions of the {sup 10}Be+n center of mass system (inelastic angular distributions) have been extracted both for Pb and C targets. For the breakup of {sup 11}Be on Pb, the selection of forward-scattering angles, corresponding to large impact parameters, is found to be effective to extract almost purely the first-order E1 Coulomb breakup component and to exclude the nuclear contribution and higher-order Coulomb breakup components. This angle-selected energy spectrum is thus used to deduce the spectroscopic factor for the {sup 10}Be(0{sup +})x{nu}2s{sub 1/2} configuration in {sup 11}Be which is found to be 0.72{+-}0.04 with a B(E1) strength up to E{sub x}=4 MeV of 1.05{+-}0.06 e{sup 2} fm{sup 2}. The energy weighted E1 strength up to E{sub x}=4 MeV explains 70%{+-}10% of the cluster sum rule, consistent with the obtained spectroscopic factor. The non-energy-weighted sum rule within the same energy range is used to extract the root-mean-square distance of the halo neutronmore » to be 5.77(16) fm, consistent with previously known values. In the breakup with the carbon target, we have observed the excitations to the known unbound states in {sup 11}Be at E{sub x}=1.78 MeV and E{sub x}=3.41 MeV. Angular distributions for these states show the diffraction pattern characteristic of L=2 transitions, resulting in a J{sup {pi}}=(3/2,5/2){sup +} assignment for these states. We finally find that even for the C target the E1 Coulomb direct breakup mechanism becomes dominant at very forward angles.« less

Subfields: Nuclear and High Energy Physics, Radiation

View Paper: https://www.semanticscholar.org/paper/50f728548fc76428f5c5194a041f8439cee2b6c4

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