Bochum 1998 – scientific programme
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HK: Hadronen und Kerne
HK 6: Spectroscopy, Light Nuclei
HK 6.3: Group Report
Monday, March 16, 1998, 14:45–15:15, D
Breakup reactions of 6,8He, 11Li, 14Be at high energies* — •J. Cub — Institut für Kernphysik, Technische Universität Darmstadt, D-64289 Darmstadt
Breakup reactions of the two-neutron halo nuclei 6He, 11Li, 14Be and of the four-neutron halo nucleus 8He were measured at GSI in complete kinematics for the fragments at energies of 240 ... 300 MeV/u. Both nuclear and electromagnetic excitations were investigated using C, CH2 and Pb targets, respectively.
Special attention will be drawn to 6He. It represents the simplest case for a theoretical description of a two-neutron halo nucleus since the basic interactions (α-n and n-n) are well understood. It will be shown that the predominant nuclear reaction channel for the AX breakup proceeds in two steps: The knock out of one halo neutron followed by the formation and decay of the particle unstable A−1X ground state resonance (e.g. 5He(3/2−)). This becomes evident from an analysis of the respective invariant mass spectrum of the A−2X-n system [1]. In addition, the detailed analysis of angular correlations between the decay products of the intermediate A−1X nuclei confirms this behaviour and, moreover, allows to determine contributions of excited states in the intermediate nuclei (e.g. 5He(1/2−)) [2,3]. The reconstructed A−1X momentum distributions reflect the internal motion of the knocked-out neutron, and thus, the projectile wave function.
The competing processes of nuclear (C target) or electromagnetic (Pb target) inelastic excitations deliver information on the multipole strength distributions in the halo nuclei, e.g. B(E1) distributions from Coulomb excitation, and on three-body correlations within the corresponding decay systems (A−2X-n-n).
[1] D. Aleksandrov et al., to be published in Nucl. Phys. A
[2] L.V. Chulkov et al., Phys. Rev. Letters 79, 201 (1997)
[3] L.V. Chulkov and G. Schrieder, Z. Phys. A359, III (1997)
* supported by BMBF and GSI