## Abstract

Breakup reactions of the one-neutron halo nucleus ^{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 ^{11}Be, outgoing ^{10}Be, and neutron in coincidence. The relative energy spectra as well as the angular distributions of the ^{10}Be+n center of mass system (inelastic angular distributions) have been extracted both for Pb and C targets. For the breakup of ^{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 ^{10}Be(0^{+}) ⊗ ν2s_{1\2} configuration in ^{11}Be which is found to be 0.72±0.04 with a B(E1) strength up to E_{x}=4 MeV of 1.05±0.06 e^{2} fm^{2}. The energy weighted E1 strength up to E_{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 neutron 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 ^{11}Be at E_{x} = 1.78 MeV and E_{x}=3.41 MeV. Angular distributions for these states show the diffraction pattern characteristic of L=2 transitions, resulting in a J^{π}=(3/2,5/2)^{+} 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.

Original language | English |
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Pages (from-to) | 54606-54601 |

Number of pages | 6 |

Journal | Physical Review C - Nuclear Physics |

Volume | 70 |

Issue number | 5 |

DOIs | |

Publication status | Published - Nov 1 2004 |

Externally published | Yes |

## All Science Journal Classification (ASJC) codes

- Nuclear and High Energy Physics